ITO Thin Films for Low-Resistance Gas Sensors

This research was funded by the Science Committee of the Ministry of Education and Science of the Republic of Kazakhstan (Grant No. AP08856540). The research was carried out with the support of a grant under the Decree of the Government of the Russian Federation No. 220 of 9 April 2010 (Agreement No. 075-15-2022-1132 of 1 July 2022). In addition, this research was partly performed at the Institute of Solid State Physics, University of Latvia (ISSP UL). ISSP UL, as the Centre of Excellence, has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD01-2016-2017-Teaming Phase2 under Grant Agreement No. 739508, project CAMART2.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. © 2022 by the authors. --//-- Published under the CC BY 4.0 license.Science Committee of the Ministry of Education and Science of the Republic of Kazakhstan (Grant No. AP08856540); ISSP UL, as the Centre of Excellence, has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD01-2016-2017-Teaming Phase2 under Grant Agreement No. 739508, project CAMART2

Microplasma breakdown in GaAs-based avalanche S-diodes doped with deep Fe acceptors

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

Avalanche delay and dynamic triggering in gaas-based s-diodes doped with deep level impurity

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

Comparative Analysis of Numerical Methods for Simulating <i>N</i>-Heptane Combustion with Steam Additive

Currently, thermal power plants operating on hydrocarbon fuels (gas, fuel oil, peat, shale, etc.) are one of the main sources of electricity. An effective and promising method for suppressing harmful emissions (NOx, carbon oxides, soot) from the combustion of fossil fuels is the injection of steam into the combustion chamber. The influence of various mathematical submodels was studied on the accuracy of the numerical simulation of the process of n-heptane combustion in a laboratory burner with steam additive to the reaction zone as a promising chemical engineering method for the disposal of substandard liquid fuels and combustible waste with the production of thermal energy. The problem was solved in a three-dimensional stationary formulation. Systematic verification of these submodels, and a comparison of the results of the calculation with the experimental data obtained were carried out. The comparison with the experimental data was carried out for gas components and temperature distribution at the burner outlet; high agreement of the results was achieved. Optimal submodels of the methodology for calculating the process of fuel combustion in a jet of steam were determined. The best agreement with the experiment data was obtained using the EDC model in combination with a mechanism consisting of 60 components and 305 elementary reactions. More correct simulation results were obtained using the RSM turbulence model and the DO radiation model

The mechanism of superfast switching of avalanche S-diodes based on GaAs doped with Cr and Fe

The results of theoretical and experimental investigation of charge carrier transport in avalanche S-diodes based on π-ν-n and π-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 π-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 depends on the applied voltage and the type of the deep-level impurity. 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 1011 V/s allows generating the voltage pulses with amplitude of 700 V and a rising edge of 250 ps at a load of 50 Ω

The mechanism of superfast switching of avalanche S-diodes based on GaAs doped with Cr and Fe

The results of theoretical and experimental investigation of charge carrier transport in avalanche S-diodes based on π-ν-n and π-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 π-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 depends on the applied voltage and the type of the deep-level impurity. 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 1011 V/s allows generating the voltage pulses with amplitude of 700 V and a rising edge of 250 ps at a load of 50 Ω

Avalanche delay and dynamic triggering in GaAs-based S-diodes doped with deep level impurity

Abstract 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

Suppression of dynamic current leakage in avalanche S-diode switching circuits

Abstract 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 ∼3–4 times, and a rise in S-diode switching voltage. The results were obtained in the experimental study and are approved by calculation

Electrical conductive and photoelectrical properties of heterostructures based on gallium and chromium oxides with corundum structure

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 radiatio

Gas sensitivity of IBSD deposited TiO2 thin films

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