It is shown for the first time that strongly directional emission of defined polarization can be achieved from conventional AlGaAs/GaAs double heterostructure surface emitting light emitting diodes (LEDs) via coupling to surface plasmons. By microstructuring the surface, LEDs were fabricated with a beam divergence of less than 4 deg and an increased quantum efficiency. It is demonstrated that the surface plasmon excitation and emission mechanism has the potential to improve the performance of LEDs. In addition, it is shown that this principle can be applied to laser diodes. A controlled outcoming of laser light by a surface plasmon coupling is demonstrated.

Within the past year significant advances in the development of high-performance vertical-cavity surface-emitting laser (VCSELs) and quantum-well modulators has been achieved. Large arrays of VCSELs with submilliamp thresholds and diffraction limited beams have been produced by MBE growth of InGaAs/GaAs strained-layer quantum-well active regions encompassed by integral AlAs/GaAs quarter-wave stack mirrors. Also, using similar technology, asymmetric transverse Fabry-Perot modulators with transfer efficiencies about 20 percent/V and high-extinction on/off modulation with voltage swing of only 2 volts have been demonstrated. Using superlattice active regions, room-temperature blue shifted absorption modulators have been produced, and self-electrooptic effect devices with record on/off ratios (more than 100:1) have been achieved.

High performance IC''s and OEIC''s rely on complex epitaxial heterostructures with tight bandgap engineering. Related developmentandproduction requires notonly very homogeneous materials but manufacturing ofqualified batches of similar wafers. Furthermore in most cases critical feature size of devices is submicronic which puts forward another important requirementconcerning surface contamination ofwafers. Thispaperpresents the breakthrough we have achieved in the above fields using especially the novel MOVPE multiwafer PLANET reactor.

High-Tc superconductor cuprates are reviewed in terms of available materials, theoretical modeling, and properties such as the relationship between Tc and hole density in the Cu-O planes. The structures are delineated for compounds including Tl2Ba2Cu1O6, Tl2Ca1Ba2Cu2O8, and Tl2Ca2Ba2Cu3O10. Specific attention is given to the key effects of grain boundaries on the physical properties of polycrystals. The superconductivity of the compounds is related to the electron (hole) pairs, and an energy gap is identified for the excitation of normal (dissipating) carriers. The penetration depth of the magnetic fields and the coherence length of the spatial extension of a Cooper pair are the primary highly anisotropic characteristics of the superconductors. The high-Tc superconductors have a variety of applications in microelectronics and optoelectronics such as Josephson junctions, the manufacturing of passive microwave devices, and the construction of superlattices.

This short overview briefly summarizes the most important parameters for successful preparation and associated properties of thin films of YBa2Cu3O(7-delta) (YBCO) superconductors. The principles are illustrated by using the example of monotarget ion beam sputtering technique: YBCO films grown in situ on SrTiO3 show Tc(onset)

An overview of applications of YBaCuO thin films is presented emphasizing the RF properties of these high-Tc superconductors and microelectronics uses with silicon-based substrates. The substrates considered include the MOS dielectrics SiO2 and Si3N4, and a low-temperature deposition processing technique for these films followed by post-annealing is detailed. The time of the rapid thermal annealing following film processing is shown to dictate the electrical and structural characteristics of the films. Rapid thermal annealing is shown to be an effective method for manufacturing superconducting films of silicon substrates, although several cycles of the process can block all superconducting properties. The use of alternative buffer layers is considered as a means for protecting against this effect in superconductors composed of silica on silicon nitride.

MOCVD and PE-MOCVD are versatile growth techniques which are capable of producing high quality YBCO superconducting films. The use of these methods to grow YBCO films with Tc in the range 88-90 K and Jc(77 K) repeatably in excess of 10 exp 6 A/sq cm is reported. This can be accomplished at substrate temperatures as low as 730 C, in the case of MOCVD, and 670 C for PE-MOCVD, through the use of N2O as the oxidant source gas. Growth at temperatures down to 570 C has been demonstrated but as the cost of Tc decreasing to 72 K. Still, these results are very promising for development of a low temperature process for the growth of YBCO which will be compatible with active device technologies.

GaAs quantum-well IR photodetectors (QWIPs) that operate at a range of peak absorption wavelengths are considered in terms of their characteristics and potential applications. The structures of some QWIPs are described with references to their band diagrams, absorption coefficients, low-temperature quantum efficiencies, and peak detectivities. Peak detectivity is shown to be temperature- and bias-dependent and to be linked to doping density, and the QWIP technology in general has high peak detectivities and good uniformity for the production of large-area 2D arrays.

The technique utilizes the capacitive coupling between a pair of Corbino electrodes and a conducting layer placed on top of and insulated from the electrodes. Measurements on heterostructures of GaAs/GaAlAs and GaAs/GaInP are reported. The audiofrequency impedance exhibits ShubnikovdeHaas oscillations. These oscillations are used to investigate persistent photoconductiity at 0. 635 tm and 1. 00 jim illumination. The role played by contacts is discussed.

The transport properties of the 2D electron gas produced by modulation doping of compound semiconductors are reviewed with attention given to the properties at high electric fields. Experimental studies are discussed in which the transport properties lead to insights into current instabilities and switching effects. The concept of electric-field-induced parallel conduction is set forth and shown to explain the current instabilities and current collapse at high electric fields. Delta doping is shown to be effective for electrooptic devices such as modulators. MQW modulators with delta-doped contacts can be used as waveguides in complicated coupler networks, or they can be optimized for a high on/off ratio by increasing device length without increasing propagation loss.

We report the fabrication characterization and physics of selectively-doped wide parabolic A1GaAs wells which contain low-disorder nearly uniform-density dilute electron systems. The electron layer in these structures has a thickness of ''''lOOOA and an effective three-dimensional density of 1x1016cm3. These structures provide a rather unique system for the studies of the single-electron as well as many-body effects in space-charge layers in semiconductors. Examples of new physical phenomena observed in these systems are presented these include: (a) the observation of plasma-shifted cyclotron resonance and (b) the collapse of the fractional quantum Hall effect in systems with large electron layer thickness. We also present the fabrication and magnetotransport measurements in a novel selectively-doped superlattice produced in a wide parabolic quantum well with a superimposed periodic potential.

We discuss the current state of knowledge concerning the three following questions : i) what is the physical system most appropriate for the observation of the Wigner transition in an electron plasma ? ii) how such a system can be optimized in order to limit competing effects like single-particle localization ? iii) which experimental techniques allow unambiguous observation of this transition ? We present the results concerning our study of dense quantum two-dimensional electron systems in low disordered selectively doped GaAs/GaAIAs heterojunctions and our evidences for a magnetically induced Wigner transition obtained concomitantly by resonant absorption of radio-frequency waves and by voltage-source transport measurements at low temperature and high magnetic field.

Interest in CdTe field effect transistors and multi-gated devices stems from the fact that CdTe is lattice matched to HgCdTe. As a consequence it may be possible to develop a monolithic technology that combines HgCdTe infrared focal plane arrays with on-board signal processing based on CdTe devices. Although CdTe metal-semiconductor field effect transistors have only recently been fabricated rapid improvement in device performance has been achieved. All the devices reported have been fabricated from CdTe:In epilayers grown by Photoassisted Molecular Beam Epitaxy. We report on devices having gold Schottky barrier with reverse breakdown voltages as high as 28. 0 V and ideality factors near 1. 7. These MESFETs exhibit good depleting mode action.

A MBE grown negative differential resistance transistor using n(+)-i-p(+)-i-n(+) structure are presented. The peak-to-valley current ratios (PVRs), peak current densities, and generated power outputs can be easily modulated by changing the third external base to emitter bias. A highest PVR of 140 with V(BE)

An ultra fast data transfer speed is demonstrated for a novel three-dimensional (3D) Static Random Access Memory (SRAM) consisting of multilayer silicon LSI chips on which GaAs LEDs and photodetectors are monolithically integrated for vertical optical interconnections. A unique feature of this system is the capability of parallel data transfer from one memory layer to the upper and lower memory layers by the optical interconnections. The results of static and dynamic simulations of the optically coupled 3D common memory have indicated that a block of 512 bits data can be transferred through four memory layers within 16 nsec. This is an equivalent data transfer speed of 128 Gbits/sec/layer.

The sensitivity of InGaAsIInP monolithic photoreceivers for 1 . 3 - 1. 5 . tm has been largely improved in recent years now reaching the sensitivity figures of hybrid InGaAs pin/GaAs MESFET receivers. The characteristics of an integrated InGaAsfJnP pin-JFET front-end based on MBE growth and diffused junctions are analysed. The results are used to illustrate some pending problems oflnGaAs FETs requiring future improvement.

Recent progress on an erbium-doped optical fiber amplifier (EDFA) pumped with a 0.98 micron laser diode is reported. An erbium-doped fiber with a very high gain coefficient of 11.0 dB/mW has been achieved using an extended VAD method. A high power 0.98 micron laser diode with a strained-layer InGaAs quantum well laser structure has been developed as the pumping light source. By employing these key components in the EDFA, a compact and highly efficient EDFA module has been fabricated successfully. The module size is only 36 cc. It attained a 33 dB net gain at 1.536 microns and it consumed only 175 mW of electricity.

Nonlinear semiconductor waveguides are investigated with respect to their use for optical bistability and temporal optical switching with results given for silicon-on-sapphire devices. The performance of the waveguides is assessed with comparisons to nonlinear Fabry-Perot cavities, and the conditions for optical bistability are theoretically shown to be possible by combining a waveguide and a diffraction-grating coupler. Structures experimentally investigated include semiconductor layers epitaxially grown on substrates having low refractive indices. Optical switching is reported on reflected or transmitted beams and on the guided-wave intensity by means of excitation pulses in the nanosecond or picosecond range. The data confirm the usefulness of nonlinear waveguides as alternative devices for temporal optical switching and logic-gate development in part due to their good switching times.

The properties are reviewed of heterostructure devices for microwave-monolithic-integrated circuits (MMICs) and optoelectronic integrated circuits (OICs). Specific devices examined include lattice-matched and pseudomorphic InAlAs/InGaAs high-electron mobility transistors (HEMTs), mixer/multiplier diodes, and heterojunction bipolar transistors (HBTs) developed with a number of materials. MMICs are reviewed that can be employed for amplification, mixing, and signal generation, and receiver/transmitter applications are set forth for OICs based on GaAs and InP heterostructure designs. HEMTs, HBTs, and junction-FETs can be utilized in combination with PIN, MSM, and laser diodes to develop novel communication systems based on technologies that combine microwave and photonic capabilities.

A review is given of III-V device performances with specific references to their use in high-speed signal processing and communications. Application-specific integrated circuits (ICs) are compared to emitter coupled logic (ECL) gate arrays in terms of density and speed, and specific attention is given to semicustom GaAs ICs. Performance and cost comparisons are presented in the form of critical path analyses and device sizes. The data-conversion applications for the III-V devices are set forth indicating that self-aligned GaAs MESFET technologies can be used for high-resolution flash ADCs because of their very low short-distance dispersions. GaAs is shown to be a viable alternative for silicon ECL and to be more useful in the fabrication of larger wafers of four inches. GaAs devices are more effective than silicon ECL if they can provide a gain of not less than a factor of five in the power-delay product.

Research efforts to bring forth epitaxial integration of elemental semiconductors (Si, Ge) and compound semiconductors (GaAs, InP, ZnSe, CdTe) in various combination thereof, are reviewed. Also reviewed are the issues relating to the growth of insulating layers on semiconductor layers for the purpose of forming SOI (semiconductor-on-insulator) for potential applications in 2D (two-dimensional) structures of 3D (3-dimensional) superstructures. First, the physics and chemistry of heteroepitaxial processes are examined along with the issues stemming from the mismatches of lattice, thermal and chemical origin. Ways to ease mismatches, using epitaxial control or intermediate layers like strained-layer-superlattice, are examined including recent progresses. Prospects for future directions along with technological implications of the semiconductor heterostructures are discussed, including a brief account of the history related to this technology.

The resonant buildup and storage of electron space charge can be enhanced in appropriately designed devices to give intrinsic bistability in the I(V) characteristics. Magnetocapacitance and photoluminescence spectroscopy measurements are used to investigate this effect and to provide evidence for the sequential model of resonant tunneling. At high magnetic fields, the intrinsic bistability effect is greatly enhanced due to the high density of states available in a Landau level.

Semiconductor structures are discussed in which the dopant impurities are arranged in an ordered or at least a partially regular manner. Various electronic properties of such arrays are examined, and it is shown how a layer of dopant atoms in silicon acts as a sensitive and tunable IR absorber.

The Hamiltonian describing the iteraction of both confined longitudinal-optical and surface-optical photons with charge carriers is derived from the macroscopic dielectric continuum model for the case of a rectangular quantum wire where photon confinement occurs in two of the three spatial dimensions. The full interaction Hamiltonian is used to calculate the total scattering rate for electron-optical-phonon scattering of electrons traversing a GaAs square quantum wire. The results demonstrate that the interaction by the surface-optical phonon modes is very strong and may dominate over other scattering processes, especially with dimensions of about 100 A or less. A considerable decrease in the total scattering rate for optical phonons as a result of simple reduction in dimensionality is not observed in this study.

Energy transfer between nanosecond light pulses interacting in a semi-insulating InP crystal is analyzed. Optically induced charge redistribution in the iron impurity states are shown to be the source of both photorefractive and absorption nonlinearities.

Some of the remarkable properties of excitonic transitions in QW structures as they pertain to devices that can make an impact on optical computing are examined. An MQW-HBT device is discussed where the large built-in gain in the device as well as the ability to control the device response optically or electronically provides a versatile building-block device. Applications of this device to thresholding switching, light ''amplification'', and programmable memory are considered, and the wavelength selective properties of excitonic detectors are explored.

Recent advances in and prospects for III-V compound semiconductor integrated optoelectronics in its application to optical computing systems are examined. Attention is given to developments concerning OEICs, photonic ICs, and optical functional devices. It is concluded that this field, due to its robustness in applications, contributes greatly to the development of optical computing systems.

The structural criteria for achieving the optimum linear and nonlinear optical response in Si-Ge superlattices is developed based on pseudopotential calculations and experimental data. A direct band gap is identified in Si(m)-Ge(n) superlattices for the condition at which m + n

Stimulated emission in indirect band-gap Al(x)Ga(1-x)As is observed at room temperature. This indirect stimulated emission is based on alloy-disorder induced zero-phonon band-to-band transitions. A quadratic dependence of the threshold pump intensity on the energy separation of the renormalized direct and indirect conduction bands is found. These threshold excitation intensities show a weak exponential increase with lattice temperature. The emission wavelength and the emission intensity close to the crossover composition are strongly influenced by band-gap renormalization, which is treated in a multivalley model. This model quantitatively explains the enhanced gap shrinkage in direct-gap AlGaAs close to the crossover composition.

Broad-area stripe geometry lasers are developed with DH InAs(0.95)Sb(0.05)/InAs(0.50)Sb(0.19)P(0.31) structures, and the emission characteristics are investigated. The lasers are grown by LPE on 100 plane InAs and emit at up to 110 K and at near 3.2 microns at 77 K with evidence of some longitudinal modes. The threshold current density at 3.2 microns is approximately 1.5 kA/sq cm corresponding to a characteristic temperature of 38 K and a quantum differential external efficiency of 4-5 percent per face above threshold. The Auger effect is predominant at temperatures of about 300 K corresponding to a threshold current density of about 30 kA/sq cm, whereas the threshold current density at low temperatures is governed by nonradiative recombination on deep centers. An internal quantum efficiency evaluation demonstrates that the maximum temperature for laser operation is 240 K.

InGaAs/AlGaAs Strained Layer Superlattices (SLS) have been grown using the MOVPE technique. These layers were characterized by X-ray, photoluminescence, photocurrent and transmission measurements. With this material optical modulators and LEDs were made working at a wavelength for which the GaAs substrate is transparent. Reverse biasing the modulator resulted in a large absorption shift in the photocurrent spectra due to the Quantum Confined Stark Effect (QCSE) on the quantum wells. An InGaAs/AlGaAs SLS compared favorably with similar InGaAs/GaAs SLSs. A back-side emitting LED, with an InGaAs SQW as the active layer, gave a maximal output power of about 8 micro-W/mA/Sr.

Bragg reflectors of three geometrical configurations are considered analytically and experimentally to solve the problem of cracking which develops due to thermal stress between the two materials used. The Bragg reflectors are based on (Ca,Sr)F2 and (Ga,Al)As and are grown by means of molecular beam epitaxy. Three geometrical solutions are considered: (1) three material combinations within quarter-wave structures; (2) mixed reflectors of GaAs-(Ca,Sr)F2 and GaAs-AlAs in shifted Bragg reflectors with reduced layer thicknesses; or (3) generalized Bragg structures based on asymmetrical geometries. The absolute or relative fluoride thicknesses in the structures can be reduced by means of the proposed configurations. Effective heteroepitaxial reflectors are set forth that have crack-free surface morphologies because the structures of the generalized Bragg reflectors reduce the stress inherent in the devices.

Epitaxial films of n-GaAs are studied at helium temperature by means of low-temperature impurity breakdown to study optical and optoelectronic bistabilities. During switching the carrier concentration is found to increase by about one order of magnitude, and the donors become ionized while achieving increased carrier mobility. The bistabilities are shown to be of interest for the design of switching elements that could include memory elements for information processing.

Data are derived experimentally for the phase diagram for high-Tc superconductors based on the (Ca(1-x)Y(X))Sr2(Tl(1-z)Pb(z)Cu2)O7. Transport, structure, and specific-heat measurements are described and discussed in terms of the relationships between the metallic/nonsuperconducting, superconducting, and insulating (M-S-I) phases of the cuprate superconductor. The conditions of normal resistivity are shown at 150 K in terms of variation with Y ions in (Ca(1-x)Y(x))Sr2(Tl0.5Pb0.5Cu2)O7, and it is shown that charge carriers at temperatures close to maximum Tc can be studied by means of thermoelectric power. Specific-heat measurements show that fluctuations of superconductivity in state II are very large near the insulating boundary where there are strong pair interactions but few carriers. A systematic trend is revealed that is a function of changing carrier concentration and that has important differences on either side of maximum Tc.

Planar photoconductors made with GaAs on silicon substrate have been studied with respect to static and dynamic responsivities as well as noise levels in the 1 Hz - 100 kHz frequency range. The results obtained have led to the determination of the specific detectivity which in turn is compared to those of GaAs planar photoconductors and Si photodiodes.

Interdigitated GaAs metalsemiconductormetal Schottky photodiodes have been studied experimentally and theoretically. The time evolution of the response current has been measured by means of photoconductive and electrooptic sampling with a time resolution of 0. 8 and 0. 3 ps respectively. The response current to a 70 fs laser pulse reaches maximum within 25 p5 then shows a fast decay of about 10 ps followed by a slower one. Selfconsistent twodimensional Monte Carlo particle simulation predicts that the former is due to electrons the latter to holes. With a sufficiently strong electric field the two species of carriers get separated. With increased light intensity a screened plasma forms that vanishes only through recombination which takes of the order of nanoseconds.

The paper reports on InGaAs interdigitated metal-semiconductor-metal (IMSM) photodetectors operational at 13 micron fabricated on GaAs substrates. Different Schottky barrier enhancement cap layers were used in order to study the thermal stability and device performance characteristics. Dark current, dc responsivity, and high frequency response results are reported. Relationship between the responsivity and the cap structure is discussed. Using oxygen plasma passivation, photodetectors with low dark current and high frequency performance were obtained.

The band-structure dependence of impact ionisation in bulk semiconductors strained Ge/Si alloys and multiple quantum well avalanche photodiodes was studied theoretically and experimentally. Hydrostatic pressure was used to investigate impact ionisation in Si Ge and GaAs. The results are interpreted with the aid of theoretically calculated threshold energies for impact ionisation. Calculated thresholds in strained Ge/Si alloys suggest that this material system may be of interest for low-noise photodetectors. However Monte Carlo studies of impact ionisation in multiple quantum well (MQW) avalanche photodiodes (APDs) show that the F valley conduction band offset does not lead to improved performance in GaAs/AlGaAs MQW APDs.

A new layer structure is investigated which consists of an In(x)Ga(1-x)As (x in the range 0.57-0.75) channel embedded in Zn-doped InP grown on an InP substrate by low pressure-MOVPE. Increasing spacer thickness leads to an increasing Hall mobility and a decreasing sheet carrier density. Photoluminescence measurements at 2 K show the high quality of the quantum wells. A transistor (2.0 x 60 microns) with Ni/AuZn/Ni ohmic contacts and a Ti/Pt/Au Schottky-gate shows a room temperature extrinsic transconductance of 11.5 mS/mm.

We have used admittance spectroscopy to characterize the DX centers in Sn doped A1GaAs and Si doped A1GaAs samples. Three peaks in conductance and the corresponding steps in capacitance are observed in the admittance spectra of Sn doped samples. It is shown that these peaks arise from the multiple states of the same physical center rather than to three different types of defects. The deepest state corresponds to the conventional DX state in the Sn doped AlGaAs probed by deep level transient spectroscopy (DLTS). The other two states are not normally observed in DLTS experiments due to experimental limitations. In the case of Si doped A1GaAs samples only one peak which is broad or slightly asymmetric is observed and it corresponds to the main DLTS peak of the Si-DX center.

We have used the luminescence upconversion technique to perform time-resolved measurements on both bulk InGaAs lattice-matched to InP and InGaAsflnAlAs multiple quantum wells (MQW) at a resolution of . ''7OOfs. For the bulk we present carrier temperatures for O extracted in the usual way from the high energy tail of transient spectra and relate this to more complete lineshape and cooling curve analyses. For the MQW we have found luminescence associated with the n subbands to be persistent to times in excess of 500ps and attribute this to real space transfer effects. In addition we compare rise and decay time data over the spectral emission ranges for the bulk and MQW.

FIR and transport measurements are undertaken on quasi-2D electron gas (2DEG) in the Quantum Hall Effect (QHE) regime of GaAs heterojunctions by means of cyclotron emission. The heating electric field is varied during the measurements which are conducted as Landau emission experiments in quantizing magnetic fields. Attention is given to the evolution of the emission spectra and the breakdown of the QHE when the electric field increases. Supplementary lines are identified in the FIR spectra that coincide with the minima of the Hall plateaus under low electric-field conditions. The nonhomogeneous distribution of the potential in the Quantum Hall state is examined to explain the supplementary lines. The nonequilibrium carrier distribution under high electric-field conditions leads to narrower Hall plateaus due to the breakdown of the equation Ns

Steady-state and time-resolved photoluminescence measurements of two double barrier GaAs/AlAs resonant tunneling structures with different barrier widths are presented as a function of bias voltage throughout the first resonance region. The confined exciton photoluminescence shows a risetime comparable in magnitude to its decay time, in the nanosecond region, and both are ascribed mainly to tunneling of the photocreated holes through the AlAs barriers. The luminescence originating from the n-GaAs contact layers, consists of two parts, a delayed and a fast component, which stem from recombination of holes which already have, and have not tunneled through the resonant tunneling structure, respectively. The general trend of decrease of the decay time with increasing bias is attributed to the increasing probability for hole tunneling through a single barrier with increasing electric field. Additional variations of the peak position, the linewidth and decay time of the confined exciton PL are directly correlated with the electron tunneling current.

Evidence of electron negative differential velocity in GaAs/AlAs superlattices is obtained from time-resolved photocurrent in n-i-n perpendicular photoconductors at 77K. The miniband widths range from 22meV to 78meV. Approximate field-velocity laws are derived using a numerical simulation relying on the drift-diffusion equations. They are interpreted in terms of the Esaki-Tsu model in which the non-linearity results from the non-parabolic miniband dispersion.

We discuss the transport time and the single-particle relaxation time of electrons in two dimensions. New results for homogeneous background doping are presented. We explain how the measurements of these two scattering times can be used to get information about the relevant scattering mechanism in disordered semiconductors. A possible metal-insulator transition is discussed.

Monolithic integration between an active and a passive waveguide directly buttjointed in a single step of MOCVD is demonstrated at 1. 5pm. The growth behavior on a patterned InP substrate is studied by using a periodic structure of GaInAs or InGaAsP/InP layers. Buried Ridge Stripe (B. R. S. ) structures consisting of a 25Ojjm long active region and 13OOjm long passive waveguide exhibit 25 mA threshold current 60 coupling coefficient and an optical output power in excess of 5 mW is measured at the passive waveguide. The monolithic integration of a distributed feedback laser coupled to a passive waveguide with this new concept is investigated.

Plasma-enhanced chemical-vapor deposition (PECVD) is demonstrated as a technique for manufacturing silicon oxynitride thin films that permit the deposition of integrated optical components on Si and III/V-semiconductors. PECVD process parameters are optimized for a conventional parallel plate reactor using silane, nitrogen, and oxygen to yield homogeneous thicknesses and refractive indices across the wafer. The waveguide types utilized for the study are strip-loaded and trench-bulge waveguides, and the SiO(x)N(y) characteristics resulting from the optimized PECVD process include homogeneity and reproducibility. Optical components can be fashioned in this manner to produce directional couplers, dielectric mirrors, fiber coupling, and integrated detectors. The trench-bulge waveguides are found to provide the advantages of zero crosstalk to neighboring waveguides, scratch protection, and improved lateral confinement.

Studies have been made of the effect of boron and fluorine impurity induced disordering on the refractive index of AlxGaixAs multiple quantum well waveguides. A grating coupler formed in low-index material was used to determine experimentally the changes in refractive index obtained in partially disordered material. Over the measured wavelength range 820-920 nm substantial changes 1 in the refractive index were observed. Fluorine was found to produce larger changes than boron for similar annealing conditions.

A periodic, electric field induced reversal of ferroelectric microdomains on (+Y)- and (—Y)- LiNbO3 surfaces was achieved for the first time at temperatures (< 400 °C) well below the Curie point. Contrary to the recently developed domain inversion processes on Z-cut substrates, no modification of the material (e.g. by a Ti-doping) nor an electron bombardment was necessary. The pyroelectric effect was used to generate an electrical field between photolithographically structured, periodic Al-electrodes on the surface of the crystal concentrating the electric field in the small volume of the microdomains to be inverted. As (+Y)- and (—Y)-LiNbO3 faces have strongly different etching rates in HF/HNO3, a successful domain reversal could be identified by selective etching. Microdomains of different dimensions (of typical 6x 15xO.25tm3), number of periodicities (100 and 1500) and periodicities (3Opm, 6.5,um and 7.6im) have been fabricated not only in undoped LiNbO3 surface layers, but also in Ti:LiNbO3 optical strip waveguides. The chosen periodicities will allow quasi-phase matched optical second harmonic generation.

We report Erbium-doped Ti-indiffused single-mode optical waveguides of good quality in LiNbO3 fabricated by Erimplantation followed by annealing. Besides ground state absorption also xcited-tate-bsorption (ESA) has been investigated indicating that even at 1. 48 pm pump wavelength ESA occurs as a three stage process. The guided-wave spontaneous fluorescence was investigated. In a " pump and probe" experiment for the first time wavelength ranges could be identified where the stimulated emission overcomes the Er-absorption.

By choice of appropriate layer thicknesses it is possible to produce GaAs/AlAs quantum well structures in which the lowest energy electron and hole wavefunctions are localised in spatially separate layers. As the low temperature radiative lifetime ol such a structure is long (ps) it is possible to observe cw optical nonlinearities at relatively low power densities. In this paper results of optical pump/probe experiments will be presented from a range of standard type II structures along with results from a new type of structure that enhances the spatial separation of the electron/hole population.

All-optical frequency conversion of an optical data signal can be achieved by a traveling-wave semiconductor laser amplifier over a spectral range given by its entire gain spectrum (1O THz). Experimental and theoretical results for the frequency conversion efficiency are presented. The effect of gain saturation and the wavelength dependence are discussed in order to find the optimum conditions for the conversion efficiency. Simultaneous conversion of an optical data signal to several wavelengths is also considered. Finally the requirements are specified for an optical filter which selects the converted data signal out of the total optical spectrum.

The pump beam intensity dependent temporal response of the two-wave mixing in InP:Fe crystals under dc fields at stabilized temperature has been studied. We observed a resonant behaviour of the rise time of the photoinduced grating like the coherent amplification gain. Numerical solutions of the coupled field and material differential equations have been performed with a time dependent fringe modulation in the sample volume. The temporal evolution of the signal beam output intensity has been described taking into account the nonlinearity effect at large modulations. Preliminary theoretical and experimental results are in rather good agreement.

We have measured the nonlinear absorption and nonlinear refractive index changes in ZnSe''ZnS multiple quantum wells at low temperature. The largest change of nonlinear refractive index is 0. 012 and corresponding n2 is 7x1Ocm2IW. The nonlinear mechanism are attributed to exciton band broadening and phase space filling of exciton states. With different excitation wavelengths we have demonstrated the dynamic optical bistabilities in ZnSe/ZnS MQWs.

The development and testing of resonant tunneling diodes with asymmetric current-voltage characteristics is described emphasizing their use as video detectors in the X-band. The I-V characteristics of a five-barrier ''graded-parameter superlattice'' structure are simulated showing a distinct asymmetry. The growth of two wafers by molecular-beam epitaxy is described in which n(+)GaAs substrates are used. The current-voltage characteristics show a significant asymmetry between forward and reverse bias, and the experimental and simulated results show discrepancies that are attributed to tunneling via the X-point. The superlattice diodes show good microwave behavior and dynamic ranges with temperature stability away from the negative differential regions that are comparable to those in Ge back diodes and better than that for Schottky diodes and pdb diodes.

A novel method for the optical testing of integrated circuits with ultrafast timeresolution and microscopic spatial resolution is described. The method is capable of detecting internal logical states switching speeds and propagation delays within complex integrated circuits as well as running times within single elements. In the experi ment a laser scanning microscope was combined with a cw modelocked argonion laser and an OBIC-stage. We achieved the complete mapping of the optical beam induced current signals in IC''s with a time resolu tion of about 100 picoseconds and a spatial resolution of less than

The first demonstration of fabrication of a monolithic photoreceiver using selective growth and lattice mismatch heteroepitaxies is presented. The photoreceiver includes a GaInAs/GaAs M.S.M. photodetector, a GaAs MESFET and a serial inductor which achieves a resonant effect. A dielectric mask was used to selectively grow the GaInAs/GaAs heteroepitaxies on the GaAs epilayers which, themselves, have been grown on a silicon substrate. In comparison with a PIN photodiode loaded with a 50 Omega resistor, approximately 10 dB gain has been obtained at 7 GHz.

Using psYAG laser controlled optoelectronic switching technique semiconductor carrier recombination times and mobilities at different conditions (different preparation carriers in different valleys) were measured Measurements of the response of a fast photodiode (about 100 ps) of a 6 6Hz transistor (50 ps) and the dispersion of a ps electrical pulse along a cable (broadening from 25 ps to about 1 ns) are reported.

The concept of selectively contacted PbTe p-n-p or p-i-n-i-p structures offers interesting new features for IR-detection. As shown by a simple model and demonstrated by photo Hall and time resolved photoconductivity measurements, an enhancement of the photoconductive response beyond the expected effect of the optically generated carriers results. Control of the response time is available by background illumination. The photo Hall effect itself represents another new detection principle.

We report the observation of Wannier-Stark localization in a InGaAs-InAlAs superlattice waveguide. Using the oblique transition connecting electrons and holes localized in adjacent wells we achieve efficient intensity modulation at 1 . 57jim incident light wavelength under TE polarization mode. A 16 dB extinction ratio is obtained by applying a 0. 75V drive voltage to a 320 j. tm long waveguide. On-state attenuation is only 3 dB.

Characteristics of reflection electroabsorption modulators such as insertion loss and contrast ratio are discussed in terms of the absorption changes. Ultimate performances and simple design equations are derived. Both InGaAs/GaAs and GaAs/AlGaAs modulators were fabricated according to the designs rules; the modulators exhibit state-of-the-art performances. For the GaAs/AlGaAs device, a reflection change of 66 percent at 5 V operating voltage was achieved with a 1.2 dB insertion loss.

The properties of a self-pumped photorefractive phase conjugator as an amplifier of amplitude modulated signal beams are investigated. In principle the crystal acts as a self-adjusting beam combiner which allows homodyne detection of the weaksignalbeam superimposed on a stronger reference beam. In our experiments the mixing takes placevia a four wave interaction process in the crystal. In this paperwe investigate the salient characteristics ofthe self-pumped phase conjugate amplifier and explain details of the beam interaction inside the ciystal.

The influence of the doping level of the InP p type cladding layer on the differentialexternal efficiency 1Dand on the threshold current density th of 1 . 5 jtm InGaAs-InGaAsP-InP quantum well (QW) lasers has been investigated experimentally and theoretically. The experimental results agree at with our model which takes into account the recombinations and the light absorption in all the layers. This allows to predict the optimum values for the optical cavity thickness and for the number of wells to lower the threshold current.

This work describes recent results investigating the operation of a novel device arrangement which is capable of being integrated using present optoelectronic materials. The system utilizes an external cavity laser diode and an avalanche photodiode (APD) in a feedback arrangement and is capable of providing a stable train of picosecond pulses without the use of saturable absorbers or external signal generators. The role of amplification in the electronic feedback circuit is examined in detail.

Both CW and pulsed diode lasers covering the wavelength region 855-912 nm have been investigated for the frequency doubling in KNbO. The influence of the spectral distribution mode character and the optical geometry of the laser beam have been investigated for several AlGaAs diode lasers. Second harmonic radiation with maximum efficiency of typically 1 has been detected both by temperature tuning CT 10-130 C noncritical phase matching) and by angle tuning. Results clearly demonstrate the critical aspects of the laser mode spectrum and the beam geometry as to the phase matching criterion in frequency doubling.

Due to created qualitative ASE model developed for the mostly wide-- spread active media we have shown that known from literature paranietera of solid state lasers with diode pumping,particularly their efficiency are exaggerated almost at order. ASE model having been supposed theoretical analysis in rectangular active element under different pump conditions and optical density are presented.

The floating silicon thin-film bridge used as a micro-heating infrared source has been analyzed and simulated for its Joule-thermal effect. It has been found that there exists an effect of temperature instability, when the current passing through the bridge is reaching a critical value. This phenomenon is attributed to the opposite behaviors of the heat conduction and the electrical resistance with respect to the temperature, and their mutual constraints in the heat flow equation. The critical heating process is also associated with a nonlinear time-delay behavior. The delay effect is reduced if the current is over the critical value. The unstable temperature is upper limited by the starting of the silicon intrinsic behavior and decreased with low impurity doping. In practical operations, the controllability of the device thus becomes difficult above this critical temperature.

Radiationinduced modification of characteristics and parameters of the GaP junctions emitting in reds green and yellowgreen spectral regiosi are st udied. A dissociation of the ZnO complexes in redemitting juntons under neutron radiation was shown for the first time. Deep level spectrum Df the gree1i and yellowgreenemitting junctions was investigated. Ionization ene rgies and capture crosssection of six donors and two acceptors centers were determine.

A comparative analysis of the effects of temperature, and electron (4.5 MeV), neutron (0.1 MeV), and gamma (1.25 MeV) irradiation on GaAs(1-x)P(x) (x

Dynamic processes in 1D superconducting superlattices (SSLs) with a period substantially higher than the coherence length are investigated theoretically. The dynamic resistive state and the nonlinear response to laser irradiation are studied. The results presented indicate that, even in large-period SSLs, a number of promising HF nonlinear phenomena may occur, which can serve as the basis for novel superconducting devices.

IR analysis shown the ratio between different CH hybridization bonds sp1:sp2:sp3 1O:O. 09:O. 81 in a-C:H layer of a-C:H/a-Se and 0:0:1 of a-C:H/KC1. The ratio between the sp3-type configurations is sp3CH:sp3CH:sp3 CH3 0. 28:0. 38:0. 34 in a-C:H/a-Se and 0. 45:0. 33:0. 22 in a-C:H/KC1. A model of the non-equilibrium crystaflization of the layer in both films is proposed. Computer simulated figures are fractals with the dimension D1 1. 37 0. 02 in a-C:H/a-Se and D2 1. 81 in a-C:H/KC1. In good agreement with the experimental data D1 1. 35 0. 04 and D2 1. 77 0. 03.

A quasi-optic resonator with a paramagnetic plane-parallel layer is considered. Stationary and non-stationary excitations of fields in such open resonator by a plane linearly polarized electromagnetic wave are studied. The dependences of the OR transmission coefficient as a nonlinear function on the magnetic component of the exciting electromagnetic field and time have been calculated assuming that magnetic susceptibility in paramagnetic is connected with the amplitude of a radio-frequency magnetic field as a nonlinear function determined from the Bloch''s equations. Bistability hysteretic phenomena and unstable operating regimes of the structure in question have been found.

Depending on the application different types of integrating cryogenic read out electronics are used for extrinsic photoconductive detectors and detector arrays. They integrate the current flowing through the detector during a given integration time by charging a capacity. To test the different detector units with respect to their sensitivity different evaluation methods are used for the determination of the noise produced by the whole assembly. To evaluate its amount different methods of signal processing as non destructive read out (NDR), correlated double sampling (CDS) and data averaging are implemented. The different methods of signal and data processing used for the tests of the detector units as well as results obtained at selected detector assemblies are presented and discussed.

The paper deals with a dynamic method for measuring the photodiode equivalent capacitance and its dependence on voltage applied Based on an original and inexpen sive modelocking technique the method uses a computer evaluation of the measured response pulse shape for a certain value of the photodiode inverse bias voltages

A nuraerical solution of the one dirriensional Schrodinger equation for an arbitrary potential profile has been conceived to be used within a transport model for semiconductor heterostructures and superlattices. This solution method achieves energy high resolution in the bound eigenstates numerical conputation this feature is particularly useful in analyzing superlattices structure where the periodic quantuni wells give rise to energy xainibands formation. The algorithni is capable to resolve between two consecutive eigenstates less than iO eV apart. This algorithm has been successfully iinplenented on a HP 340 desktop coTriputer.

The design and realisation of NTD Silicon rods in the vertical channel 45/6 of the VVRS Nuclear Reactor from Mgurele Bucharest is described. Special attention was paid to the 0th''0f ratio influence on the thermal annealing done in order to remove neutron radiation damage. An optimal way achieved for obtaining best longitudinal resistivity distribution on rods is presented. The evolution of the defects was studied using optical and resonance methods. Some mechanisms explaining the radiation damage and its removal by means of a proper thermal treatment are exposed.

Current-voltage characteristics of a resonant tunneling diode are studied by including the effects of the conservation of transverse momentum at the heterojunction interfaces, energy-band nonparabolicity, and the temperature dependence of effective mass. The results are significantly different from the previous calculations, in which these effects are neglected. The present calculations can also explain the experimental results: (1) peak current density is the same at 77 K and at 300 K, and (2) the voltage position of the peak for 77 K is lower than that for 300 K. Also, the discrepancy between the experimental and the theoretical values of the voltage at which the peak occurs is reduced.

To overcome the discrepancy existing between the well known therinionic emission and drift-diffusion models particularly critical in arbitrary graded isotype heterojunctions a unified transport model has been considered. The algorithm is based on a simultaneous numerical solution of the one dimensional Poisson and Boltzmann equations using an iterative method to obtain the self-consistent potential and distribution functions for every polarization condition. I .

Based on Shockley diffusion theroy we proposed an injection current model for the metaloxide- semiconductor (MOS) charge injectioii device (CID) under charge sharing mode readout scheme. It is found that the injection current is proportional to the inverion charge concentration afl(l the exl)onential of surface potential divided by thermal voltage i. e. the relation follows the famous ideal (liode equatioii. In Or(ler to verify the model we develop a photocurrent method to measure the injection curreiit versus surface potential characteristics of a silicon MOS capacitor. Jl experimental results are in good agreement with the ideal diode equation afl(1 the ideality factor is very close to unity. Based on this model we also derive the equivalent SPICE circuit for the single-gate CID.

We perform an analytical calculation of the capacitance of a single quantum well versus the applied bias using a " multi space charge regions approximation" . This model is able to reproduce the experimental behaviour of such a structure and is validated by a comparison with a complete numerical simulation. Secondly we describe using the thermionic emission theory the behaviour of carriers in the well when the structure is out of equilibrium. With these two models we obtain the capacitance transient using a very light computer calculation. This analysis shows that the capacitance transient is not exponential in contradiction with previous works. Using Deep Level Transient Spectroscopy we determine the band offset of a GaAs/GaInAs/GaAs single quantum well and compare the results with the one obtained using Capacitance-Voltage measurements associated with a complete numerical approach 778 / SPIE Vol. 1362 Physical Concepts of Materials for Novel Optoelectronic Device Applications Il: Device Physics andApplications (1990)

In transport the creation of hot LU phonons causes a reduction in the carrier energy relaxation rate but an enhancement of the momentum relaxation rate. The magnitude of the latter determines the drift velocity attainable at high electric fields - which in turn limits the speed of devices such as FETs. How big this effect is depends on the rate of relaxation of phonon drift. Mechanisms for this relaxation are discussed and phonon-momentum relaxation rates are calculated for bulk and layered structures. Processes considered include the FrOhlich interaction with charged impurities phonon-phonon scattering and scattering at interface irregularities. We conclude that the quality of the material structure is crucial.

Experimental results on high-field parallel transport in GaAs/GaAlAs quantum well structures are presented. The results are compared with a theoretical model of high field transport involving non-drifting hot phonons and scattering from remote impurities and interface roughness. The latter two effects contribute to the relaxation of the electron momentum. It is also shown that non-drifting hot phonons with a fmite life-time reduce the energy relaxation and enhance the momentum relaxation. The enhancement of the momentum relaxation at high fields inhibits negative differential conductivity via real space transfer or intervalley transfer. This is observed in our samples. The reduction of the drift velocity at high fields is also detrimental to the speed of many devices which operate in the hot electron regime.

We used electro-optic voltage probing to map the potential distributions along a degenerate single quantum well that exhibited current oscillations when subjected to high fields at low temperatures. The results given here were obtained over a wide range of field strengths at room temperature. The potential profiles were found to contain some very unusual features which might be indicative of the poor quality of the barrier material in this sample.

The effects of layout parameters on the gain response speed noise behaviour and sensitivity of a hybrid optical receiver consisting of a three stage GaAs monolithic transimpedance amplifier and a detector using SPICE has been analysed. The BFL type configuration consisting of an inverter and buffer/level shift circuit was chosen for the amplifier design. The simulated results predict the optimised layout parameters for the targeted gain of 100 with 300 Mbit/Sec data rate and 40 dBm sensitivity for CEERI''s 1/um gate length GaAs MESFET technology.

To allow an extremely sensitive measurement of optically induced changes of the index of refraction in a Ti:LiNbO3 stripe waveguide a specific two wavelengths " excite and probe" technique has been recently developed [1J taking advantage of the large phase sensitivity of a waveguide resonator. A resolution of Ln 5 x iO has been achieved which is nearly two orders of magnitude better than demonstrated with conventional methods. For both polarizations and for several wavelengths in the visible and near infrared the most important parameters characterizing the photorefractive effect could be determined. They were evaluated by analyzing the measured index changes using a widely accepted theoretical model adopted to the waveguide geometry.

Different techniques for fabrication of single-mode waveguides in silicon by etching and indiffusion are reported. Minimum propagation losses around 3dB/cm at a wavelength of 1. 3Lm have been achieved.

The paper presents an approach to the nondestructive ellipsometric investigation and computer simulation of dielectric structures with known thicknesses. Three-dimensional profile studies of surface microrelief using an atomic force microscope are also considered. The proposed approach enables the examination of an optical waveguide''s sections and permits investigations of interferometric coatings and the numerical analysis of various multilayer dielectric systems.

Some improvement of technology making the coupling of a fiber to a stripe waveguide more simple and effective is presented. The improvement consists in additional reprocessing of the edgeadjacent area of a substrate slab with a fabricated stripe waveguide. The mentioned area is subjected to a proton exchange process with simultanous drawingup of the slab from meltAfter a supplement process in the edge adjacent area the waveguide has a form of a horn with convergency depending on the mask pattern velocity and the melt temperatureAt the entrance face of the slab the channel takes a form of a rectangle of sizes of about tens micrometers wide and up to a few micrometers deep. The coupling of a fiber to an enlarged channel waveguide has been efficiently simplified and the coupling power is not so sensitive to the offaxial and tilt deflection of the fiber. L Interconnection of QjiCa1 wavides In most integrated optics devices a light beam is guided in a stripe waveguide of a required configuration. Low power electrooptical modulation forces decrease of the waveguide width. In photo-and electronolitography processing the stripes of width up to 2 pm have been manufactured1''2. The depth of about 0. 5 im is required for guiding of one mode. Long distance transmission realize fibers. Geometrical crosssection of the both fiber and stripe differ in size and form espe cially for multimode waveguides and the

Photocurrents in the ampere range were generated and optically quenched, respectively, in a new type of semiconductor switch on a nanosecond timescale using two lasers of different wavelength. The semi-insulating switch material is GaAs, doped with silicon and compensated with copper, which forms sets of deep acceptors below the middle of the band gap. The photoconductivity in this system is generated by electron and hole ionization from these centers and subsequent fast hole retrapping. Quenching of the photoconductivity is accomplished by hole ionization from copper centers and subsequent electron-hole recombination. The densities of Cu/Si related defects in the various deep levels determine the switch efficiency and its temporal response to the laser pulses. This distribution is very sensitive to variations in the processing procedure of the switch material. Besides photocurrent measurements, Photo-induced Current Transient Spectroscopic (PICTS) studies have been performed in order to determine the activation energy of the deep centers. Additional informations on the deep-level structure of GaAs:Si:Cu were obtained by cathodoluminescence spectra and decay experiments at cryo-temperatures.

Mechanisms of saturation absorption of IR-FIR radiation in semiconductors with degenerate band structure are investigated. As a result of this investigation a mode-locking device for pulsed IR gas lasers is developed and investigated. Using p-GE filter cooled to 78 K as the saturation absorber inside the laser resonator, subnanosecond IR laser pulses are obtained from a tunable high pressure CO2 laser. These pulses were transferred into FIR region via stimulated Raman scattering of CO2 radiation and as result tunable subnanosecond FIR laser pulses are obtained. The device permits the generation of a train of short pulses lasting 1 ns and accordingly from FIR laser. Semiconductor photoelectric detectors for subnanosecond IR-FIR radiation pulses are also described.

Microscopic dynamics. of materials can be studied by time delayed four-wave mixing spectroscopy. Dephasing constants can be measured by such experiments. Experimental results are easily analysed when the correlation time r of the exciting electric field is much shorter than the dephasing time ''2 However when these quantities are on the same time scale numerical fits are necessary. In the present work we analysed theoretically a time delayed four-wave mixing experiment. The material is described by an ensemble of two-level systems and a large inhomogeneous broadening is assumed. Using the third order term of the density matrix we establish a relation between 1''2 -r and ''Tm the time delay for which the maximum of the diffracted light intensity is observed. The conditions to obtain an estimate of T2 from the measurement of Tm are discussed.

The well known magneto optical selection rule 4 for two photon interband transitions between the Landau levels of semiconductors without inversion symmetry is shown to be violated when the component of the optical wave vector perpendicular to the magnetic length is not negligible respect to the inverse of the magnetic length. The total transition rate calculated out of the electric dipole approximation and with the adoption of a gauge independent description of the radiation matter interaction Hamiltonian is presented. As an application the case of GaAs and InP is considered.

InGaAs/InGaAsP-multi-quantum--well-layers are preferably used as the active region in long-wavelength semiconductor lasers. In this work we present calculations of their optical gain in dependence of the carrier density . These calculations are compared with measurements of electrically and optically excited gain spectra of such laser structures for 1. SSim emission wavelength with different numbers of wells. In contrast to conventional double heterostructure lasers a distinct sublinear increase of the gain g with increasing carrier densities N is observed which is well pronounced for low well numbers and can be described approximately with a logarithmic equation g''''ln(N) quite in accordance with theoretical predictions.

We report on optimum conditions for the diffusion-controlled growth of C4Se-microcrystallites (MC's) near the nucleation stagehaving a very small and symmetric size distributiolL Temperature dependent linear absorption measurements and room-ternperature ps-hole burning spectroscopy have been performed for material chaiacterization and for the determination of MC-parameters. The influence of MC-glass interface states on the nonlinear optical behaviour is studied investigating the bleaching behaviour and its kinetics at surface passivated (hydrogenated) and at non-passivated samples.

Problems in the fabrication of homogeneous integ ited lenses on lithium niobate were investigated. TIPE and double proton exchange waveguide . abrication methods were compared and various masking systems tested. Mode matching between a v w index single mode DMPE waveguide and a high index multi mode PE waveguide was optimized.

The present study has demonstrated the feasibility of transmitting polarization-coded optical information by optical fibers and their ability to operate with optical logic elements. Several simple arrangements of optical fibers joined with fibers have been examined. Sufficient coupling efficiency in the arrangements examined has not been achieved. The maximum SNR in the guidelines investigated was 10:

Reported about building solidstate laser with rectangular active element. In high power regime laser with active element from neodimium doped GGG crystal became power l8OWt by repetition rate 25Hz and absolute efficiently 3. By beam divergence near lOmrad specific power raising compose 7. 5Wt/sm The interest to the lasers with rectangular active elements including lasers with waveguide active elements (1 is based mainly on the fact that these lasers allows to obtain high average power generation regime under simultaneous suppression of thermooptical effects (3 Maximum efficiency of such lasers at lamp pumping is for the best samples up to 2-2. 4 [5. 7]. Along with for the mostly powerful lasers (7] pulse repetition rates are in the interval 35c '' as far as for real high average power regime frequencies more than lOc are characteristic. The results of studing solid state laser with rectangular active element on the base of 0(30 crystal doped by Nd are presented below. Laser designed have demonstrated record value of efficiency at repetition rate up to 25c . Compact double-side illuminator to supply symmetrical illumination of active element was used. Active element lateral surface cooling was provided due to immediate contact with coolant (distilled water with chromium oxide O. 5g/l). Laser resonator length was 650 mm. Plate dielectric mirrors were used out mirror refraction coefficient being varied in experiments. Activators ions concentration in the chosen active

High-Tc YBaCuO thin films have been prepared on polycrystalline zirconia substrates by low-temperature RF diode sputtering, followed by a rapid thermal annealing. A Tc(R

Low pressure MOVPE in a horizontal reactor has proven to be capable of yielding uniform lnP, GalnAs and GalnAsP layers /1 , 2/. However, the complexity of some devices as MOW lasers and HEMTs require even further improve — ment in thickness and compositional uniformity. This can be achieved by using the technique of substrate rotation to overcome gas phase depletion problems and geometry related non uniformities. Techniques for the pratical realization of such systems using a mechanical drive have been described earlier /3/. However, the technical solution for substrate rotation, using mechanical feed throughs was only applied to small, laboratory scale systems. In this paper we will discuss the use of the new 'gas foil rotation' technology for growth in a low pressure reactor. In this technique the wafer holder is floating on a foil of high purity hydrogen. Since the hydrogen is forced to flow with a circular component, the plate with the substrate is put into rotational motion /4, 5/. lnP, GalnAs and GalnAsP layers grown in a single wafer reactor on 2' substrates applying this substrate rotation show film thickness variations less than 2% over the entire wafer. Resistivity measurements on doped binary layers showed variations of less than 2%. The lattice mismatch variations of ternary and quaternary layers was below 5x104. The electrical properties of GalnAs and nP as residual carrier concentration and electron mobility in undo— ped layers were identical to those measured on reference layers grown in the same reactor on a static susceptor. Growth parameters had not to be modified when using this technique. The gas foil rotation assembly does not require mechanical drive parts, feed through etc., and thus does not generate particles; it can easily replace the standard static susceptor with only minor changes in the gas supply system. The method has also been applied in multiwafer reactors, where the wafers rotate in 'planetary" motion. Similar results have been obtained in a horizontal reactor with 5 wafers rotating in planetary motion. The growth of GaAs/AlGaAs heterostructures and InGaAs with outstanding film properties and high requirements on film homogeneities such as HEMTs /1 , 2/ has been demonstrated in an atmospheric pressure reactor designed for 7 wafers rotating in planetary motion in a radialsymmetric horizontal flow system.

Magnetic freezeout experiments under hydrostatic pressure have been per formed in the dark before and after successive illuminations on barely metal lic nA1GaAs (x 32) and n-GaAs samples. In both cases evidence is given for a shallowdeep bistability behavior of deep defect states near the metal insulator transition. In nAl Ga As the lightinduced transformation of the x 1x deep DXtrap into its metastable effectivemasslike configuration is demons trated allowing to monitor the shallow donors concentrations in a wide range across the Mott density. In nGaAs evidence is given for pressureinduced elec trical activity of the EL2 defect metastable configuration which is found to act as an acceptorlike resonant level whose occupation affects strongly ''the concentration of the shallow donor states in almost a similar way as in the ca se of the DXstates in nAl Ga As. x 1-x

Deep donor levels are observed in Al(x)Ga(1-x)As for x of greater than 0.22 and GaAs under hydrostatic pressure (for p of more than 2GPa). Persistent photoconduction (PPC) is the most striking feature of this deep donor, the DX center. Upon illumination at low temperature, the free-electrons concentration increases and remains at this new value even after the light is off. Basically the DX centers are photoionized and one (or several) electrons per center are transferred to the conduction band. The bistable character of the donor which involves two electronic configurations is studied by Moessbauer spectroscopy (MS). Electronic wavefunctions, near-neighbor geometries and lattice vibrational properties can be probed. Moessbauer spectroscopy is used to observe the Sn DX center in Al(x)Ga(1-x)As near x

The paper presents ns-hole-burning experiments of the quantum-confined transitions in CdSe quantum dots. By means of respective model calculations the contribution of inhomogeneous and homogeneous broadening of the spectra are deduced at 77 K and room temperature. Tuning the excitation wavelength over a broad spectral range demonstrates a common blocking of three electronic states about 160 meV apart.

Progress in the area of integrated receivers is surveyed, with emphasis on the use of large lattice mismatch epitaxy, selective growth, and planar structure to reduce the technological difficulties associated with the fabrication of these integrated circuits. Some examples of monolithic integration of photodetectors with transistors and optical waveguides are presented. Particular attention is given to a monolithic resonant photoreceiver for long-wavelength and microwave applications, fabricated using lattice mismatch heteroepitaxies and selective growth.

The investigation results of preamplirier (PA) based on a current emitter amplifier a stage enabling to realise the bipolar transistor pO8sibilities in the most erfective was in constructing a lownoise wideband PA operated by highohmic signal sources i. e. highspeed photodiodes are presented in the paper. I.