There is great interest in materials for one-transistor capacitive memory elements (1T1C DRAM) based on a non-junction gate FET with high memory density. ZnO film is an interesting material for creating such memory, since dielectric properties of ZnO can be controlled by donor or acceptor impurity. The goal of this study is the investigations of the dielectric properties and mechanisms of charge carrier transport of ZnO and ZnO:Li films in wide frequency and temperature range to demonstrate the possibility of creating a memory element that combines a capacitor and a field-effect transistor. ZnO:Li dielectric layer can be used as channel of the FET and dielectric for capacitor. Proposed DRAM have good potential for memory applications because it has a high reading speed; the ratio of currents in states "1" and "0" is about 105 , and the holding time exceeds 10 ms.
We present an n-type channel transparent field-effect transistor (FET) using a top-gate configuration on a sapphire substrate. ZnO:Li film was used as channel, and MgF2 film - as gate insulator. Measurements showed that ZnO:Li films are ferroelectrics with spontaneous polarization Ps = 1–5 mkC/sm2 and coercive field EC = 5–10 kV/sm. The dependences of drain-source current on drain-source voltage at various gate-source voltages in two antiparallel Ps states were measured and the values of field-effect mobility and threshold voltage were determined for two Ps states: a) μ = 1.5 cm2/Vs, Uth = 30 V; b) μ = 1.7 cm2/Vs, Uth =23 V. Thus, Ps switching leads to a change in FET channel parameters. Results can be used to create a bistable or, more precisely, digital FET.
The memristor element for random access memory (resistance random access memory - ReRAM) was developed and investigated. The developed structure consists of a Schottky diode (1D) based on Pt/ZnO:Ga/ZnO/Pt heterostructure and a memristor (1R) based on Pt/ZnO:Ga/ZnO/ZnO:Li/Pt heterostructure. Thus the unipolar memristor memory element of 1D1R type was obtained. The heterostructures were produced by the electron-beam vacuum deposition method. The laboratory samples of the memory elements were prepared and their characteristics were studied. The proposed device has a high stability and withstands 1000 switching cycles without derating.
We are presenting a novel photoplethysmographic (PPG) optical sensor and device with ambient optical, electrical and electromagnetic noises cancellation, thus allowing only the useful optical signals to be received by the health monitoring device. We are also presenting a new processing technique for canceling the ambient noises contributed by optical, electrical and electromagnetic artifacts in the measured PPG signals. Such a device and method allow the enhancement of the performance of the PPG sensors compared to conventional apparatus and methods. The presented sensor and methodology have been integrated into a prototype standalone device for noninvasive, continuous, wearable, remote and mobile monitoring of blood pressure and other human vital signs, such as heart rate, oxygen saturation, respiration rate, etc This small device allows the user to read, store, process and transmit all the measurements made using the PPG optical sensor and the electronic unit to a remote location.
We studied experimentally the granular structures prepared on the base of ZnO thin films. The influence of acceptor or
donor complex, caused by oxygen vacancy and interstitial zinc atom, and impurities (Li or Ga) on the crystallite
structure conductivity has been investigated. The effect of granule size and crystallite structure on conductivity and
photoconductivity was studied. The new method for determination of electric current dependence on spatial coordinates
in thin conducting film was developed, which allowed to diagnose a one-dimensional conductivity in ZnO:Ga films. The
experimental results are interpreted on the basis of the scaling hypothesis and the percolation theory.
The peculiarities of charge carrier transfer mechanism in ZnO films doped by donor or acceptor impurity and
metal−dielectric electronic phase transition were investigated. The control parameter of this transition is concentration of
interstitial Zn atoms. The films with high concentration of interstitial Zn atoms have high conductivity of metallic type.
Air annealing leads to change of conductivity temperature dependence from metallic type to dielectric one.
We report the preparation and investigation of ferroelectric field effect transistors (FET) using ZnO:Li films with high field mobility of the charge carriers as a FET channel and as a ferroelectric active element simultaneously. The possibility for using of ferroelectric FET based on the ZnO:Li films in the ZnO:Li/LaB6 heterostructure as a bi-stable memory element for information recording is shown. The proposed ferroelectric memory structure does not manifest a fatigue after multiple readout of once recorded information.
We present two approaches for production of periodically poled lithium niobate crystals by surface modification of
congruent crystals: first - by Li enrichment during annealing and second - by deposition a thin layer of stoichiometric
lithium niobate film on the +Z face of a crystal. Both methods have allowed to create on the surface of congruent sample
a layer with composition close to stoichiometric and to reduce a poling electric field without changing of the
composition of crystal volume and thereby to keep all advantages of congruent crystal.
We report the preparation and investigation of heterostructures based on ferroelectric crystals and semiconductor films.
The ferroelectric field effect transistor with high transparency for visible light and high field mobility of the charge
carriers has been fabricated using ZnO:Li films as a transistor channel. The possibility of use of ferroelectric field effect
transistor based on ZnO:Li films as bistable element for information writing has been shown.
It is shown, that correct choice of complex forming ligand in the gel allows obtaining oriented ZnO films even on
amorphous substrates. On crystalline substrates, in the case of small mismatches between lattice parameters of the
substrate and the film, the main reason for the film orientation is epitaxial growth of ZnO film.
In contrast to the case of liquid-phase epitaxy, the spontaneous polarization in epitaxial growth of lithium niobate films
by the sol-gel method is directed normally from the substrate.
We report on highly efficient diode-pumped solid-state (DPSS) green laser source based on a monolithic cavity
microchip laser platform. The use of periodically poled MgO-doped Lithium Niobate (PPMgOLN) as the nonlinear
frequency doubler together with gain material Nd3+:YVO4 allows obtaining a significant increase in the overall
efficiency of green microchip laser in comparison with other compact green laser source architectures with comparable
output power. We discuss our progress in miniaturization and efficient operation across a wide range of temperatures
and application-specific modulation conditions. In particular, we demonstrate 50mW-120mW average green output
power (30% duty cycle) with wall-plug efficiency over 13%. Efficient laser operation with duty cycle ranging from 10%
to 60% in a wide range of repetition rates is also demonstrated. The laser is designed to be a part of the miniature and
efficient RGB light source for microdisplay-based (LCOS, DLP or similar) mobile projector devices. While these
projection architectures typically require modulation rates from 60Hz to about 2000Hz depending on design, we
extended modulation speed up to 2MHz that can be of interest for other applications. A very efficient and small
microchip as well as alignment-free design allow us to package this laser source into the very small volume of only
0.23cm3 (bounding box). We present results of performance tests for this packaged laser and demonstrate that such a
miniature package can support laser operation with average power output of over 250mW.
Very important advantage of ZnO thin films is an opportunity of use in the composite heterostructures opening
opportunities for development of ZnO-based optoelectronics devices. In this work we report the preparation of
ferroelectric crystal - ZnO thin film heterostructures by vacuum deposition method and creation of new type of
pyroelectric photodetector. The ferroelectric field effect transistor has been prepared using ZnO:Li films as transistor
channel and LiNbO3 and TGS crystals as pyroelectric sensitive element. The photoelectric properties (currents ratio,
charge carriers mobility, ampere-watt sensitivity in IR diapason, NEP sensitivity, and photocurrent kinetics) of prepared
heterostructures were investigated and first samples of novel pyroelectric photodetector with high sensitivity and
detectability were prepared.
Recent developments in compact projectors sparked interest in light sources for these applications. While RGB lasers
offer advantages, a viable green laser platform has been difficult to realize. In this work, we demonstrate a novel green
laser source, based on a monolithic cavity microchip laser platform. The use of highly efficient, periodically poled MgOdoped
Lithium Niobate (PPMgOLN) as the nonlinear frequency doubler allows obtaining a significant increase in the
overall efficiency of the green microchip laser. Specifically, we demonstrate 50-150mW green output with wall-plug
efficiency exceeding 10% in the temperature range over 40°C. We discuss a compact package for this laser source with
volume less than 0.4cm3.
A key stage in production of the integrated optics devices is forming of microtopography on crystalline films. The
current methods generally comprise two separate steps: producing of thin film and creation a topographical pattern on it.
But the inherently large chemical stability of crystalline LiNbO3 has effectively precluded the use of standard
photolithographic patterning techniques. We present new approach based on the modified sol-gel technology using the
photosensitive gel. In this case, the photolithography is used on the stage of dried gel whereupon the direct
crystallization of patterned precursor film allows to create integrated optical element without subsequent etching of
crystalline film. Presented method of patterned thin film preparation involves synthesis of photo-reactive complex of
metal, which undergoes change under the UV light. This technology has allowed to obtain first samples of different
types of waveguide devices.
Both n-type and p-type ZnO will be required for development of homojunction light-emitting diodes and laser diodes. It
is easy to obtain strong n-type ZnO, but very difficult to create consistent, reliable, high-conductivity p-type material.
Here we present our investigations of p-type ZnO thin film preparation by sol-gel method using single Li doping and
Ga(Al)+N codoping technique. ZnO thin films with c-axis orientation have been prepared on glass substrates. Zn acetate
dihydrate, gallium nitrate and acetamide were used as zinc, gallium and nitrogen precursors respectively. SEM, X-ray
diffraction, electric conductivity and Hall effect measurements were carried out. The results show that p-type conducting
ZnO films with hole concentrations as high as 5x1017 cm-3 were obtained by this method.
We present our studies on preparation of LiNbO3 oriented stoichiometric thin films by sol-gel method. The technology
of synthesis of precursor systems, containing Li and Nb, has been developed. Studies of structure, morphology, optical
and physical properties were carried out. The lattice parameters have been determined and correspond to stoichiometric
lithium niobate crystals. The crystallographic orientation of LiNbO3 films corresponds to orientation of a sapphire
substrate, i.e. on substrates with orientation (0001) the C axis of film is perpendicular to a substrate surface, and on
(11-20) substrate C axes lays in a plane of a substrate. The developed method allowed to obtain lithium niobate thin
films with 300-700 nm thickness, transparent, with precise crystallographic orientation both on sapphire substrate and
conductive ZnO films.
Optimization of transparent conductive and textured-dielectric coatings to increase the efficiency and reflectance control is very important for solar cell applications. The developed technique has allowed us to obtain Li doped ZnO films with high transparency and low dark conductivivity. Measurements of dark and photoconductivity were carried out over a wide frequency range (0-1010 Hz). Photoelectric property studies have shown that with Li doping, it is possible to achieve an essential increase of photoconductivity. This phenomenon can be used for development of solid-state photodetectors in the UV range (290-340 nm). The current-voltage characteristics, current-optical power sensitivity and kinetics of rise and decay times of slow and fast components of the photoresponse were studied. It was found that the dark current and photocurrent have different conductivity mechanisms: hopping mechanism of charge transfer in the Hubbard model impurity band for dark conductivity current and drift mechanism of charge transfer in the conduction band for photoconductivity current.
Lithium niobate crystals used in quantum electronics and integrated optics are mainly doped by different impurities in order to strengthen or suppress one or another property. Here we discuss the influence of hafnium impurity on photorefractive and photoelectric properties of lithium niobate crystals. The investigations of photorefractive effect in hafnium doped lithium niobate crystals have shown the possibility of suppression of photorefraction in these crystals (up to 3 orders). The experimental results demonstrate that the suppression of photorefraction occurs as a result of correlated increase of crystal dark and photo conductivities by 5 orders which is explained by significant increase of polaron mobility in the conduction band. One of the possible causes of the polaron mobility increase is the modification of the phonon spectrum of the crystal and a reduction of polaron scattering on defects associated with the lithium deficiency.
Recently the experiments demonstrating the advantages of direct optical control of ferroelectric domain profiles have been carried out. Here we present our findings and detailed analysis on time dependence of the ferroelectric coercive field after domain inversion of the LiTaO3 and LiNbO3 crystals. We have investigated the mechanisms of light influence and possibilities of optical control of domain structures in ferroelectrics, in particularly the roles of the various internal field components, their origins and dynamic behavior following domain reversal. Our experiments have shown the possibility of direct optical control of domain patterning in ferroelectrics.
ZnO thin film is the perspective material for using as active layer in solid-state UV photodetectors. Here we present our investigations of photoelectric properties of the developed photosensitive field-effect transistor. Pure and lithium doped ZnO films were produced by vacuum electron-beam deposition method. Field effect was studied in Li doped ZnO films having high resistivity and in heterostructures consisting of three ZnO layers doped by 1, 5 and 10 at% of Li impurity accordingly. The photoelectric characteristics were measured (currents ratio, charge carriers mobility, ampere-watt sensitivity in UV diapason, NEP sensitivity, and photocurrent kinetics). The open and close current ratio was 106 and the field-effect mobility was ~10 cm2/Vsec. We have also studied the low-frequency noises (0.001÷100 kHz) of UV photodetector and suggested the methods of noise suppression. It was found that the dark current noises and photocurrent noises have different mechanisms.
Periodicaly poled LiNbO3 single crystals with antiparallel domain configurations have been successfully grown with a (010) oriented seed from a congruent melting composition with 4 mol % potassium addition using a modified Cz geometry. The experiments reported in this paper showed that the polarization antiparallel domain structure in lithium niobate crystals can be created during growth process by a direct poling technique with electric field of alternating polarity. PPLN strucutres with period length 20-100 μm were demonstrated by this method.
Several methods have been applied to obtain the crystals with regular domain structures. The most common ins the use of patterned electric field poling, but the quality of resultant periodically poled material can depend on a number of factors and periodicities below approximately 3 micrometers are difficult to produce however, particularly with simultaneously large aspect ratios. Here we present an alterative method for production of periodically patterned domain structures due to optical periodic poling, a technique involving the simultaneous applications of combined electrical and optical fields: the electric field is applied via planar electrodes, while light is used to define those regions where domain inversion should occur. The optical poling route therefore offers a potentially simpler method, effectively eliminating the photolithographic patterning steps. Using interferometric methods, the periodicity of optically induced domain structures is a function of laser wavelength, and intersection angle of the two interfering beams, and hence is easily changed. We present also the investigations of the mechanisms of optical control of domain structures in ferroelectrics, in particularly the roles of the various internal field components, their origins and dynamic behavior following domain reversal.
The sharp increase of photoconductivity current fluctuations is observed experimentally in lead molybdate crystals for definite values of exciting radiation intensity. The mechanism explaining the arising of anomalously great fluctuations of photoconductivity current in lead molybdate crystals taking into account the spatial-temporal dependence of photoconductivity current is proposed on the base of quadratic low of photoelectronics recombination. The experimentally observed anomalously great fluctuations of photoconductivity current are explained by 1D soliton arising in the photoconductor.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.