We describe in this paper the design and characteristics of buried heterostructure (BH) distributed feedback (DFB) lasers grown by low pressure metalorganic chemical vapor deposition (LP-MOCVD). Typically, threshold current is 30mA for 240µm-long lasers with two cleaved facets and 40mA for lasers with one facet anti-reflection coated. Experimental values are in good agreement with theoretical predictions, based on the laser structure and the coupling coefficient of the diffraction grating. Single longitudinal mode operation is observed for temperatures up to 70°C and output powers up to 6mW. The mode rejection ratio between the DFB mode and the strongest side mode is greater than 30dB.

In three previous papers (Refs. 1-3), some of the key features and advantages of tne new 1.523µm HeNe laser were outlined and compared with those of a diode laser. To get the max-imum use out of this ultra-monocnromatic laser source, it is necessary to stabilize the laser frequency for such applications as heterodyned fiber-optic communications and fiber gyros.

A computer program for the evaluation of the threshold current of ridge-waveguide lasers has been realized. The current dependence on the thickness and composition of the various layers has been investigated with the aim of optimizing the device structure with respect to the threshold current.

A number of modified DCPBH laser devices were realized, which can be driven as a single transistor (or as a number of parallel transistors). The devices allow direct and seperate measurement of various leakage components in DCPBH devices, i.e. electron- c.q. hole-hetero-barrier leakage and blocking layer leakage. Measurements on these devices lead to a good understanding of leakage phenomena and of device performance of DCPBH laser diodes. Measured data serve as input for accurate modelling of DCPBH devices.

Optical communications systems increasingly need to make use of single longitudinal mode (SLM) lasers so that fibre dispersion does not degrade system performance. At gigabaud rates over long distances with conventional Fabry Perot lasers dispersion will limit performance even in the low dispersion 1.3 μm windows, or at 1.5 μm with dispersion-shifted fibre. Various single frequency laser structures have been used, but the distributed feedback (DFB) laser and variants of it using internal gratings for feedback have become the most popular SLM devices. It is desirable that an SLM laser should operate stably to high output powers; we show here for the first time that high power DFB operation is limited by asymmetric longitudinal spatial hole burning effects which are critically dependent on facet reflectivity and phase.

Dynamic linewidth broadening (chirping) and intersymbol interferences are investigated theoretically and experimentally for injection lasers under high speed modulation conditions (2 Gbit/s). "Below steady state"charge storage effect and "falling edge" chirping are presented. Chirping fluctuation from bit to bit is shown. Pulse shaping techniques can reduce these detrimental effects.

A low threshold current (≈30 mA) 1.3µm (InGaAsP) second order DFB laser with a ridge structure made by liquid phase epitaxy is reported. The low threshold results from : optimized heterostructure and grating profile, good tuning of the DFB wavelength with the peak gain wavelength, and the proper LPE regrowth conditions on the grating.

The selectivity of coherent detection facilitates the use of wavelength-division multiplexed systems to exploit the bandwidth of monomode optical fibre. Optical amplifiers offer the possibility of gain in such systems without demultiplexing. The amplification of a pair of multiplexed signals with an antireflection-coated semiconductor laser has been demonstrated. It was found that the internal gain and resonant wavelengths varied with the power in the second channel, and that amplitude-modulated signals consequently caused crosstalk. From measurements of crosstalk against interference power, it was concluded that phase or frequency modulation will normally be preferable to amplitude modulation in multiplexed systems with amplifiers.

Low band-gap III-V solid solutions such as GaInAsSb, AlInAsSb and InAsSbP, grown on GaSb or InAs substrates, have potential applications in optoelectronics in the long wavelength range 2.0-4.5 μm. In the first part of this paper a survey of some properties of III-V alloys which can be matched with GaSb is presented. The band-gap energy E0, the spin-orbit splitting Δ0 and the refractive index n of a few GaSb-lattice-matched quaternary systems are calculated as a function of the alloy composition. The use of these solid solutions in light sources and detectors is discussed on the basis of the Auger effect, which can be strong whenever E0 ~ Δ0. In the second part we present our results concerning the LPE growth of the GaInAsSb / GaSb system. Lattice-matched 2.0-2.4 μm and quasi lattice-matched 2.0-2.5 μm quaternary layers could be epitaxied in the temperature range 450-600°C. Double heterostructures using Ga Sb and GaAlAsSb as confining layers, matched with (100) GaSb, were prepared. From the analysis of phase diagram and growth problems, the applications of GaInAsSb / GaSb heterostructures grown by LPE on GaSb appear to be limited to the 1.7-2.4 μm and 4.3-4.7 μm wavelength range.

In(As1-x-yPxSby) is one of the most attractive III-V compound for optical sources with wavelength in the range 2-4µm. Liquid phase epitaxy of this quaternary alloy lattice-matched to InAs substrates was studied. Growth of a high band gap confinement layer, limited by the presence of an immiscibility domain, was optimized from phase diagram calculations. In(AsPSb)/InAs/In(AsPSb) heterostructures, which give the best confinement of the active layer and the longer emission wavelength of this system, were successfully grown.

Strained-Layer Superlattices,obtained by alternate MBE growth of Inx1Ga1-x1As and Inx2Ga1-xAs on InP substrates, were grown lattice matched to InP. Such structures, which involve only ternary alloys, allow any emitting wavelength in the range 1.6 to 2µm.

The Travelling Heater Method has been applied to the crystal growth of CdxHgl-xTe for infrared applications. The main characteristics and advantages of this method are presented with regard to the two most important metallurgical difficulties of CdxHgl-xTe : mercury pressure and phase segregation. Metallurgical and electrical properties of the ingots are presented.

Avalanche photodiodes (APD) based on bulk grown Cd0.7Hg0.3Te ( λ = 1.55 µm) offer significant advantages over the diodes fabricated from group III-V and group IV semiconductors. Metal Organic Chemical Vapour Deposition (MOCVD) is a well established technique for the growth of CMT (CdxHgl-xTe) (0<x<1). The interdiffused multilayer process (IMP) has been implemented on a computer controlled MOCVD system to improve the compositional uniformity of epitaxial films grown by this technique. Currently, this technique is giving compositional uniformity of ≈3% over 1 cm2 on CdTe substrates.

Lead-chalcogenide diode lasers are useful as mid-infrared sources (2-1/2 <λ<30 µm), but have generally operated CW below 100K. A new materials system, PbEuSeTe, has been used to fabricate diode lasers operating from 10K (at 6.5 µm wavelength) up to 174K CW (at 4.4 μm) and up to 280K pulsed (at 3.8 µm). These are large optical cavity single quantum well devices grown by molecular beam epitaxy. These are currently the highest diode laser operating temperatures ever achieved at these wavelengths to our knowledge. Single ended output powers as high as 1 mW single mode (5 mW multimode) have been attained from mesa stripe diodes. These characteristics make these devices attractive for long wavelength fiber optic sensor/communications systems. The performance limits of these devices will be discussed.

Experimental results are reported on the coherence properties and low frequency noise of index-guided AlGaAs diode lasers with optical feedback. The coherence length, Lc, of the laser field is strongly dependent on the amount of feedback and feedback phase, provided Lc is larger than twice the external cavity length. A coherence collapse is observed for high levels of op-tical feedback. Three excess noise peaks have been observed and are attributed to external cavity mode - and diode cavity mode hopping. The results will be discussed using a theoretical analysis for the nearly-coherent feedback and fully-incoherent feedback cases.

The properties of electro-optic waveguide devices in GaAs, such as propagation and coupling loss, reflections, driving requirements, bandwidth, polarization sensitivity and on/off ratio, have to be optimized to allow their application as high-speed modulators in single-mode optical communication links. By using electron beam masks, lift-off and reactive ion etching techniques for the fabrication of rib waveguides in n-/n+ GaAs we have achieved device losses of less than 5 dB for both Mach-Zehnder interferometers and stepped A directional couplers. Reflections from the coupling facets were reduced to less than .5% by SiO antireflection coatings. The driving voltages are between 10 V and 30 V and the modulation/ switching bandwidths exceed 5 GHz. Results of system applications at data rates of more than 500 Mbit/s are reported.

In this paper some of the special features of the Pb-salt materials system which deserve special attention are reviewed. These include: lattice matching considerations, substrate preparation, liquid phase epitaxy from supercooled solutions and surface passivation. Lattice matching of a multilayer heterostructure is important since a mismatch as small as Δa/a ~ 10-3 causes many dislocations and results in poor device performance and degradation. A special mechanochemical, contactless polish has been developed to prevent any physical contact between the substrate surface and even a soft pad. Thus a bulk-like quality substrate without subsurface damage can be routinely obtained. The liquid phase epitaxial growth for heterostructure multilayers is used with highly supersaturated solutions to enhance nucleation. The lattice matching was found to be quite important during both growth and dissolution under near equilibrium conditions. A flat interface can be easily sustained when the solid in equilibrium with the melt is lattice matched to the substrate. Device emphasis in this review is on a buried heterostructure injection laser which exhibited a stabilized longitudinal mode behavior under CW operation from ~15K to above 70K. Lasing power transfer to a mode, 20-40 cavity modes away, was attributed to a "grating"-like influence imposing an additional constraint on the laser spectrum. The native passivation scheme studied resulted in substantial improvement in electrical characteristics, an increase in the RoA product of p-n junction detectors of small area devices, and a decrease of the Jth of injection lasers at low temperatures.

Conventional interconnect and switching technology is rapidly becoming a critical issue in the realization of systems using high-speed silicon and GaAs-based technologies. Optical interconnect technology promises to enhance performance significantly, provide relief from the pinout problem, decrease implementation complexity, and provide improvements to the flexibility of systems by allowing real-time reconfiguration of these systems. By releasing the bandwidth constraints on interconnects, the full processing speed capabilities of silicon and GaAs logic can be exploited to dramatically improve system throughput. Using existing silicon IC technology and discrete GaAs optoelectronic components, we have been developing techniques for chip-to-chip optical interconnects for high-speed communications. In addition, we are studying the impact of high-speed optical interconnects on computing and architecture development for future systems. Results of this work are presented in this paper.

The attractiveness of monolithic InGaAs PIN-FETs for high-speed, long haul optical transmissions at 1.3 -1,6 µm is presented. The requirements of monolithic integration of PIN photodiodes, junction FETs and biasing/feedback resistor are discussed and the fabrication process and operating characteristics of integrable PIN photodiodes and J-FETs grown by Molecular Beam Epitaxy 'are then given.

The chip technology and properties of both JFETs and pin photodiodes designed for opto-electronic IC's in InGaAs material grown lattice-matched on semi-insulating InP:Fe substrate are presented. The p-n junction of the devices were fabricated by p-diffusion from Zn-doped spin-on films. For the chip technology a self-aligned process has been developed.

This paper reviews the general requirements for the design and technology of InP/In1-xGaxAsyP1-y PIN and avalanche detectors suitable for high speed and low level detection in the 1µm - 1.6µm wavelength region. Results on different type of InP based photodiodes are presented.

Germanium p+n avalanche photodiodes with various diameters have been fabricated in order to investigate the change of the device properties with size. From SIMS profiles and reverse characteristics of test diodes appropriate diffusion conditions for the guard ring are derived. The dark current obtained from diodes 50µm in diameter is as low as 70nA at 90% of the breakdown voltage. At room temperature the multiplied fraction of the dark current can be lowered from 30nA to 6nA by reducing the diameter of the diodes from 100µm to 50µm. Although multiplication factors of M≈500 have been observed, the region with uniform gain shrinks with increasing multiplication. With a gain of M= 25 spot scans of the photo-response only show an area of 30um in diameter to exhibit almost uniform multiplication within the active area of a 50µm diode.

The main physical properties of the Hgl-xCdxTe alloys are presented with some special features (matching of bandgap and spin orbit energies). Experimental measurement of life-time have been made on THM crystal with low doping levels. It is concluded that the dominant recombination mechanism is radiative. Hgl-xCdxTe photodiodes are described operating at various wavelengths such as 1.3-1.55-2.3 µm. These PIN and APD detectors exhibit high performances (low dark current, high hole/ electron ionization coefficient ratio, high RoA product). The capability of using Hgl-xCdxTe material for emitting devices has been investigated. The electroluminescence effect in PN junction has produced emission lines at 1.35 - 1.52 and 2.5 µm with interesting narrow linewidths.

The use of optical interconnects in systems incorporating complex Si circuits could significantly reduce the number of wire interconnects required for such systems. One possible approach to the development of optical interconnects is the monolithic integration of AlGaAs optoelectronic devices and Si circuits. However, the differences in crystal properties between GaAs and Si present a severe impediment to the growth of high-quality GaAs on Si. This paper will review recent advances in lasers and other opto-electronic devices fabricated on MGS substrates.

The integration technology of a ridge AlGaAs/GaAs waveguide laser grown by MOCVD and of a microelectronic circuit is described in two different configurations: a selective and a non-selective laser layers growth. The critical steps of the respective processes are then compared.

High quality epitaxial layers of PbTe, PbSe, and (Pb,Sn)Se have been grown onto Si wafers. Epitaxy was achieved using graded (Ca,Ba)F2 buffer layers grown by MBE. The buffer layer serves for lattice match. It consists of CaF2 at the Si interface (mismatch 0.6%) and changes to BaF2 with a 14% increased lattice constant for match at the interface to the IV-VI lead-salt narrow gap semiconductors. Smooth, crackfree surfaces have been obtained. Mobilities in the IV-VI's reach bulk values over the whole 300K-10K range. Near BLIP-limited photovoltaic IR-detectors are demonstrated in nonoptimized layers. The results open up the possibility to combine large monolithic linear or area focal plane arrays (FPA) of intrinsic IR-detectors with signal processing in the Si wafer. - Epitaxial (Ca,Sr,Ba)F2 may find further applications as graded buffers to connect different non lattice matched semi-conductor layers with lattice constants between about 0.54 and 0.62nm.

The semiconductor material system InGaAsP on InP is being increasingly used for waveguide based electro-optic devices such as phase modulators, directional coupler modulators, and switches with the long term goal of opto-electronic monolithic integration. We have demonstrated the fabrication of long passive rib waveguides (RWG) with low optical losses (3dB/cm) in this material. Electro-optical light modulation was achieved employing a p-n junction. The linear, quadratic and cubic term of the electro-optic effect could be identified. Design rules for high efficiency modulators is proposed.

We report on the first monolithic integrated transimpedance photoreceiver operating at 0.85 µm wavelength using GaAlAs-GaAs heterojunction phototransistor (HPT) and heterojunction bipolar transistors (HBT). The design and the fabrication process are presented, taking into account the specific characteristics of high current gain-high speed HPT and HBT. Using 26 kΩ external feedback resistor the monolithic photoreceiver has a bandwidth of 80 MHz with a transimpedance gain of 7000 V/A and a sensitivity of -30 dBm. These preliminary results are very closed to the theoretical performances predicted for this circuit capable to operate for local network optical links at 140 Mbits with a sensitivity of -40 dBm.

A new GaInAs PIN photodiode, and GaAs integrated circuit pre-amplifier are reported for applications in long wavelength high data rate fibre-optic receivers. This combination is seen as a first step towards full integration by exploiting state of the art GaAs integrated circuit, and GaInAs/InP optoelectronic technology. Receiver sensitivity of -37.5dBm at 680 Mbit/s have been obtained with this approach with bandwidth of greater than 700 MHz.