Data on the sensitivity of Ga2O3/GaAs:Cr heterostructures are presented to long-wave and UV (λ = 254 nm) radiation. The samples were obtained by RF magnetron sputtering of a gallium oxide film on non-heated GaAs:Cr substrates. Gallium arsenide plates with a Ga2O3 film were divided into two parts: one half was not annealed, and the other was annealed in argon at 500°C for 30 min. Regardless of the presence or absence of heat treatment, the studied structures exhibit a photovoltaic effect and are able to operate in an autonomous mode. It is shown that a noticeable sensitivity to long-wave radiation appears in the samples only after thermal annealing of gallium oxide films. The response and recovery times of such UV radiation detectors do not exceed 1 second.

Pt/(100) β-Ga2O3 Schottky barrier diodes were fabricated using a plate cleaved from the crystal grown by Czochralski method. Their electroconductive and photoelectric characteristics were studied. The following values were obtained: the Schottky barrier height (1.69/1.62/1.74 eV), ideality coefficient (1.09/1.14), saturation current density (9.91 × 10–15 A/cm2), diode series resistance (7.98 kΩ), and net donor concentration [(1.8–2.4) × 1018 cm–3]. The diodes demonstrate a high rectification ratio of 1010 at an applied voltage of ± 1 V and a relatively low experimental value of the leakage current density ∼10–11 A/cm2. These structures are solar-blind and also capable of operating in self-powered mode. The diodes are highly sensitive to short-wave ultraviolet radiation with a wavelength λ ≤ 265 nm. The maximum values of responsivity (20.4 A/W), external quantum efficiency (1.2 × 104%), and detectivity (9.6 × 1015 Hz0.5 × cm × W–1) of diodes were registered under exposure to irradiation at λ = 210 nm and at applied voltage of −1 V. The responsivity and external quantum efficiency values in the self-powered operation mode were 12.3 A/W and 7.2 × 103%, respectively. The diodes showed low rise and decay times in self-powered operation mode for photodiode based on Ga2O3: 14 and 30 ms, respectively.

α-Ga2O3/α-Cr2O3 heterostructures with a corundum structure were obtained by chloride vapor phase epitaxy and magnetron sputtering. The structural, electrical conductive and photoelectrical properties of the obtained samples were studied. It was established that the α-Ga2O3/α-Cr2O3 heterostructures exhibits weak rectifying properties and in comparison with α-Ga2O3 films has a higher response speed when exposed to ultraviolet radiation Keywords: Gallium oxide, chromium oxide, corundum, anisotypic heterostructures

The work compares the switching efficiency of avalanche S-diodes in 1-D drift-diffusion (DD) and hydrodynamic (HD) models. It investigates low-voltage S-diodes with a switching voltage of V-S approximate to 150-180 V operating in current pulse generation circuits with a pulse duration of 1.7 ns (base pulsewidth) and an amplitude of approximate to 30 A. The residual ON-state voltages across S-diodes are attributed to such processes as recombination, ohmic conduction, and nonohmic conduction caused by the avalanche generation of carriers during the formation and movement of ionizing domains. The generation of ionizing domains makes the greatest contribution to switching losses, which require a certain voltage to be maintained on the S-diode. A HD approach was discovered to quantitatively describe the switching behavior for the most efficient S-diodes with a residual voltage of 0.24V(S). Low-efficiency S-diodes with a residual voltage of up to 0.48V(S) are supposedly switched by small-diameter conducting channels (no more than 14.2 mu m). Unlike the DD approach, the HD approach produces 2.5 times slower switching and a higher residual voltage in S-diodes, which are due to wider ionizing domains originated in conducting channels.

The Cr2O3-NiO mixed oxides' thin films were formed by means of the layer-by-layer magnetron sputtering deposition of Cr2O3, NiO, and Cr2O3 layers on c-plane sapphire substrates. These thin-film structures, subjected to subsequent annealing, constituted a combination of the monocrystalline (0001) Cr2O3 and nonordered nickel oxide phase, which was a mixture of NiO and Ni2O3. The annealing at 900 and 1000 degrees & Scy; in air facilitated the diffusion of Ni and Cr atoms into the layers. Varying the annealing time allowed us to control the uniformity of the Ni and Cr distribution, the microrelief of the film surface, the transmittance in the visible region, and the sheet resistance of the Cr2O3-NiO thin-film structures. Thus, the films annealed at 900 degrees C during 30 min were characterized by a uniform distribution, a relatively weakly developed surface, a low sheet resistance, and the highest Haacke's Figure of Merit of 1.49 x 10(-9) Omega(-1). The formation of mixed Cr2O3-NiO oxides by the proposed approach was found to be an effective way to improve the performances of Cr2O3 based p-type transparent conductive electrodes.

Deep centers and their influence on photocurrent spectra and transients were studied for interdigitated photoresistors on α -Ga 2 O 3 undoped semi-insulating films grown by Halide Vapor Phase Epitaxy (HVPE) on sapphire. Characterization involving current-voltage measurements in the dark and with monochromatic illumination with photons with energies from 1.35 eV to 4.9 eV, Thermally Stimulated Current (TSC), Photoinduced Current Transients Spectroscopy (PICTS) showed the Fermi level in the dark was pinned at E c −0.8 eV, with other prominent centers being deep acceptors with optical thresholds near 2.3 eV and 4.9 eV and deep traps with levels at E c −0.5 eV, E c −0.6 eV. Measurements of photocurrent transients produced by illumination with photon energies 2.3 eV and 4.9 eV and Electron Beam Induced Current (EBIC) imaging point to the high sensitivity and external quantum efficiency values being due to hole trapping enhancing the lifetime of electrons and inherently linked with the long photocurrent transients. The photocurrent transients are stretched exponents, indicating the strong contribution of the presence of centers with barriers for electron capture and/or of potential fluctuations.

The structural and gas-sensitive properties of n-N SnO2/κ(ε)-Ga2O3:Sn heterostructures were investigated in detail for the first time. The κ(ε)-Ga2O3:Sn and SnO2 films were grown by the halide vapor phase epitaxy and the high-frequency magnetron sputtering, respectively. The gas sensor response and speed of operation of the structures under H2 exposure exceeded the corresponding values of single κ(ε)-Ga2O3:Sn and SnO2 films within the temperature range of 25–175 °C. Meanwhile, the investigated heterostructures demonstrated a low response to CO, NH3, and CH4 gases and a high response to NO2, even at low concentrations of 100 ppm. The current responses of the SnO2/κ(ε)-Ga2O3:Sn structure to 104 ppm of H2 and 100 ppm of NO2 were 30–47 arb. un. and 3.7 arb. un., correspondingly, at a temperature of 125 °C. The increase in the sensitivity of heterostructures at low temperatures is explained by a rise of the electron concentration and a change of a microrelief of the SnO2 film surface when depositing on κ(ε)-Ga2O3:Sn. The SnO2/κ(ε)-Ga2O3:Sn heterostructures, having high gas sensitivity over a wide operating temperature range, can find application in various fields.

Indium tin oxide thin films were deposited by magnetron sputtering on ceramic aluminum nitride substrates and were annealed at temperatures of 500 °C and 600 °C. The structural, optical, electrically conductive and gas-sensitive properties of indium tin oxide thin films were studied. The possibility of developing sensors with low nominal resistance and relatively high sensitivity to gases was shown. The resistance of indium tin oxide thin films annealed at 500 °C in pure dry air did not exceed 350 Ohms and dropped by about 2 times when increasing the annealing temperature to 100 °C. Indium tin oxide thin films annealed at 500 °C were characterized by high sensitivity to gases. The maximum responses to 2000 ppm hydrogen, 1000 ppm ammonia and 100 ppm nitrogen dioxide for these films were 2.21 arbitrary units, 2.39 arbitrary units and 2.14 arbitrary units at operating temperatures of 400 °C, 350 °C and 350 °C, respectively. These films were characterized by short response and recovery times. The drift of indium tin oxide thin-film gas-sensitive characteristics during cyclic exposure to reducing gases did not exceed 1%. A qualitative model of the sensory effect is proposed.

The MSM structures based on high-quality 1.6- $\mu \text{m}$ -thick $\alpha $ -gallium oxide (Ga2O3) films grown by the halide vapor phase epitaxy with Ti/Ni interdigital contacts were developed for the detection of short-wave ultraviolet (UVC) radiation. The spectral dependences of responsivity, external quantum efficiency (EQE), and detectivity of MSM structures based on $\alpha $ -Ga2O3 were studied in the wavelength range of 205–260 nm. The responsivity, the EQE, and the detectivity are $7.19\times104$ A $\times \,\,\text{W}^{-{1}}$ , $3.79\times105$ arb.un., and $1.12\times1018$ Hz $^{\text {0.{5}}} \times $ cm $\times \,\,\text{W}^{-{1}}$ , respectively, for structures with an interelectrode distance of 30 $\mu \text{m}$ at an applied voltage of 10 V and exposure to radiation with a wavelength of 235 nm. The high values of the photoelectric characteristics were caused by the manifestation of an internal gain of the photoresponse due to the self-localization of holes in $\alpha $ -Ga2O3. The prospects of researches to develop UVC radiation detectors for wireless UVC communication were shown.

The article reports investigations into the microplasma breakdown in GaAs‐based avalanche S ‐diodes doped with deep Fe acceptor impurities. The experiment shows the effect of current limitation in a reverse I–V curve with “soft” avalanche breakdown. It proposes 2D single microplasma models and calculates I–V curves of diodes with a deep impurity during microplasma breakdown. By comparing experimental and calculation data, authors propose an explanation for the effect of current limitation during avalanche breakdown. The effect is associated with capture of avalanche holes at negatively charged Fe centers, which enhances the depletion region and minimizes the maximum electric field in a reverse‐biased p – n junction of an S ‐diode.

TiO2 films of 130 nm and 463 nm in thickness were deposited by ion beam sputter deposition (IBSD), followed by annealing at temperatures of 800 °C and 1000 °C. The effect of H2, CO, CO2, NO2, NO, CH4 and O2 on the electrically conductive properties of annealed TiO2 thin films in the operating temperature range of 200–750 °C were studied. The prospects of IBSD deposited TiO2 thin films in the development of high operating temperature and high stability O2 sensors were investigated. TiO2 films with a thickness of 130 nm and annealed at 800 °C demonstrated the highest response to O2, of 7.5 arb.un. when exposed to 40 vol. %. An increase in the annealing temperature of up to 1000 °C at the same film thickness made it possible to reduce the response and recovery by 2 times, due to changes in the microstructure of the film surface. The films demonstrated high sensitivity to H2 and nitrogen oxides at an operating temperature of 600 °C. The possibility of controlling the responses to different gases by varying the conditions of their annealing and thicknesses was shown. A feasible mechanism for the sensory effect in the IBSD TiO2 thin films was proposed and discussed.

This work investigates the dynamic current leakage of ${S}$ -diode, which is a GaAs-based avalanche switch doped with deep Fe acceptor traps. The dynamic leakage has negative effect on superfast switching parameters of this unique device, and here we suggest an original way of reducing the leakage by means of circuit design. It is shown that an additional bias for avalanche S-diode in the current pulse generation circuit forms a negatively charged layer of iron traps near the electron-injecting junction. As a result, the concentration of nonequilibrium electrons goes down, which leads to a decrease in leakage current by $\sim 3$ -4 times, and a rise in S-diode switching voltage. The results were obtained in the experimental study and are approved by calculation.

The article is concerned with a detailed switching delay effect exhibited by avalanche S-diodes-superfast GaAs closing switches doped with deep Fe centers. The current and voltage time dependences are simulated in a simplified generator. The dynamic electric field and charge profiles in the structures are calculated. This article describes an impact that Fe capture cross sections of free charge carriers have on delayed switching. The simulation results show that delayed switching is associated with deep center recharging in a double injection mode due to three different processes. There are two different delay mechanisms to be herewith distinguished. A delay effect is experimentally viewed to control the dynamic switching voltage (and the avalanche breakdown voltage) using constant voltage adjustment capability enabled by a triggering circuit supply. The authors demonstrate the way it is possible to adjust the amplitude of current nanosecond pulses in the range of 20-45 A through a lidar transmitter circuit with a semiconductor laser and nonoptimized S-diode. The findings are consistent with the results of numerical simulation.

The effect of ultraviolet radiation and a strong electric field on the conductivity of structures based on two types of polymorphic gallium-oxide films is studied. Both types of Ga2O3 films are obtained by hydride vapor phase epitaxy on smooth and patterned sapphire substrates with the orientation (0001). In one and the same process, on smooth substrates, α-Ga2O3 films are obtained and, on patterned substrates, gallium-oxide films with regular structures perpendicular to the substrate containing alternating regions of α- and ε-phases are deposited. Resistive structures based on two-phase films exhibit a transition from a state with low resistance to a state with high resistance under the action of radiation with λ = 254 nm and a strong electric field. The time of response to UV radiation is 5 s, and the recovery time is shorter than 1 s.

Here we report on the influence of various gases on electrical properties of Pt-contacted alpha-Ga(2)O(3)and alpha-Ga2O3/epsilon-Ga(2)O(3)structures produced by halide vapor phase epitaxy on planar and patterned sapphire substrates. Pt-contacted alpha-Ga(2)O(3)structures were highly resistive and exhibited no sensitivity to H(2)and other gases. In contrast,alpha-Ga2O3/epsilon-Ga(2)O(3)structures grown under the same conditions on patterned sapphire substrates exhibited clear and reversible response to H-2. The response to H(2)was thoroughly investigated at temperatures ranging from 25 degrees C to 200 degrees C and at applied biases from 1.5 V to 150 V. The lowest detectable limit of H(2)at 125 degrees C was found to be 54 ppm. Selectivity of Ga(2)O(3)structures against O-2, NH3, CO, CH4, and H2O was examined at 125 degrees C and 200 degrees C. The structures showed little or no sensitivity to other gases at bias voltages below 7.5 V. Electrical and hydrogen sensing properties of these structures can be explained by a model of two back-to-back connected Schottky diodes which is widely used to describe metal-semiconductor-metal structures. Catalytically active Pt electrodes play an essential role in hydrogen sensing mechanism as they promote dissociation of hydrogen molecules. Accumulation of hydrogen atoms at Pt/epsilon-Ga(2)O(3)interface results in the reduction of the Schottky energy barrier and current increase.

The results of theoretical and experimental investigation of charge carrier transport in avalanche S-diodes based on pi-nu-n and pi-n structures are presented. High-ohmic layers of the diodes were made by diffusion of deep chromium and iron acceptors into n-GaAs. It is shown that recharge of the deep acceptors in the avalanche regime should lead to expansion of the space charge region into the pi-layer and formation of step-type current-voltage characteristics rather than the S-type. It has been found experimentally that the switching of the S-diode is superfast ( the time of switching is less than the transient time of the carriers through the active region). The obtained results are in contradiction with the earlier proposed mechanism of deep-level recharging. Thus, this mechanism has been revised. The comparison of the obtained results with the literature data allows one to find the only mechanism of superfast switching, which is associated with generation of collapsing field domains due to the Gunn effect under the avalanche breakdown condition. According to the experiment, the switching time of S-diodes dependson the applied voltage and the type of the deep-levelimpurity. The S-diodes can operate in relaxation oscillator and sharper circuits. The use of the S-diodes in a sharper circuit with a moderate voltage rate of 10(11) V/s allows generating the voltage pulses with amplitude of 700 V and a rising edge of 250 ps at a load of 50 Omega.

The results of studying the effect of the thickness of GaN barrier layers in the active region of LED structures with InGaN/GaN quantum wells on the internal quantum efficiency (IQE) of photoluminescence are presented. It is shown that a decrease in the thickness of the GaN barrier layers from 15 to 3 nm leads to an increase in the maximum value of IQE and to a shift of the maximum to the region of high excitation powers. The result obtained is explained with consideration for the decrease in the Auger recombination rate due to a more uniform distribution of charge carriers over the active region in structures with a barrier thickness of 3 nm.

The result of studies of resonant tunnelling of charge carriers in InGaN/GaN unipolar structure is presented. Authors show that at temperatures below 150 K the multiple negative-differential resistance regions are observed on a reverse current-voltage characteristic which is typical for inhomogeneous distribution field for sample with 6 nm barrier thickness. At GaN barrier thickness 3 and 12 nm resonant tunneling were not observed.