Effect of oxygen on the electrical conductivity of Pt-contacted α-Ga2O2/ε(κ)-Ga2O3 MSM structures on patterned sapphire substrates

Electrical conductivity and gas sensitivity of α-Ga2O2/ ε(κ)-Ga2O3 structures were measured for oxygen concentrations ranging from 2 % to 100 % and temperatures ranging from 25 °C to 220 °C. It was found that the oxygen sensitivity of the structures depended on the donor dopant concentration. The alpha -Ga _{2}O_{3}/arepsilon ( kappa )-Ga 2 O 3 structures doped with sim 1.5 imes 10^{17} cm −3 of Sn showed high sensitivity to O 2 in the temperature range from 180 °C to 220 °C and at the bias voltage below 7.5 V. This effect can be attributed to the chemisorption of oxygen molecules on the surface of structures, which reduces energy barriers between ε(κ)-Ga2O3 grains

HVPE growth of corundum-structured α-Ga2O3 on sapphire substrates with α-Cr2O3 buffer layer

Gallium oxide films were grown by HVPE on (0001) sapphire substrates with and without α-Cr2O3 buffer produced by RF magnetron sputtering. Deposition on bare sapphire substrates resulted in a mixture of α-Ga2O3 and ε-Ga2O3 phases with a dislocation density of about 2∙1010 cm-2. The insertion of α-Cr2O3 buffer layers resulted in phase-pure α-Ga2O3 films and a fourfold reduction of the dislocation density to 5∙109 cm-2

Self-powered photo diodes based on Ga2O3/n-GaAs structures

The electrical and photovoltaic characteristics of the Ga2O3/n-GaAs structures have been studied. A gallium oxide film was obtained by HF magnetron sputtering on n-GaAs epitaxial layers with concentration of N_d=9.5·1014 cm-3. The thickness of the oxide film was 120 nm. Measurements at a frequency of 106 Hz have shown that the capacitance-voltage and conductance-voltage dependences are described by curves characteristic of metal-insulator-semiconductor structures and exhibit low sensitivity to radiation with λ=254 nm. When operating on a constant signal, the samples exhibit the properties of a photodiode and are able to work offline. The photoelectric characteristics of the detectors during continuous exposure to radiation with λ=254 nm are determined by the high density of traps at the Ga2O3/GaAs interface and in the oxide film. Keywords: MIS-structures, capacitance-voltage characteristics, volt-siemens characteristics, photocurrent, trap density

Structural, electrical and gas-sensitive properties of Cr2O3 thin films

Cr2O3 thin films were synthesized by RF magnetron sputtering of a Cr target in an oxygen-argon plasma. The effect of annealing temperature on the structural, electrical, and gas-sensitive properties of the Cr2O3 thin films was studied. According to AFM, SEM, XRD, EDX, XPS, optical spectroscopy and electrical measurements the annealed films were characterized by a polycrystalline structure, high stoichiometry, p-type conductivity and a band gap energy of 3.3 ± 0.2 eV. An increase in the annealing temperature from 350 to 450 °C leads to formation of Cr2O3 grains with a diameter from 30 to 130 nm and to a significant increase in the film electrical resistance. Cr2O3 demonstrated sensitivity to NO2, H2, NH3, vapors of acetone and toluene in the heating temperature range of 25–200 °C. Changing the annealing temperature allows to control the sensitivity of the films to certain gases. Thus, Cr2O3 thin films subjected to annealing at a temperature of 450 °C were characterized by a high response to NH3, while those annealed at a temperature of 400 °C – to toluene vapors and that annealed at 350 °C – to NO2 and acetone vapors. A qualitative model of the sensory effect was proposed

Oxygen Sensors Based on Thin Films of Gallium Oxide Modified with Silicon

The results of an investigation of the electrical resistivity of Ga2O3 thin films modified with silicon under the influence of oxygen in the range of O2 from 9 to 100 vol. % and changes in the heating temperature of structures from 25 to 700 °C were presented. Thin films of Ga2O3 were obtained by RF magnetron sputtering of Ga2O3 targeted with pieces of Si on the target’s surface in oxygen–argon plasma. The possibility of developing selective oxygen sensors based on thin films Ga2O3 modified with silicon with a temperature of maximum response 400 °C was shown. Oxygen influence leads to a reversible increase in the samples’ resistance, due to the chemisorption of oxygen on the surface of thin Ga2O3 films. An increase in the response of sensors based on the thin polycrystalline films of gallium oxide modified with silicon is caused an increase in the adsorption centers for O−, due to an increase in the surface inhomogeneity and the appearance of additional adsorption centers Si4+

β-Ga₂O₃ Schottky Barrier Diode with Ion Beam Sputter-Deposited Semi-Insulating Layer

Vertical Schottky barrier diodes based on an ion beam sputter (IBS)-deposited β-Ga2O3 film on a single-crystalline (2¯01) unintentionally doped (UID) β-Ga2O3 with a Ni contact were developed. To form ohmic Ti/Ni contacts, the IBS-Ga2O3/UID β-Ga2O3 structures were wet-etched, and an indium tin oxide (ITO) intermediate semiconductor layer (ISL) was deposited on the opposite surface of the UID β-Ga2O3. The IBS-deposited Ga2O3 layer was polycrystalline and semi-insulating. Low leakage currents, rectification ratios of 3.9 × 108 arb. un. and 3.4 × 106 arb. un., ideality factors of 1.43 and 1.24, Schottky barrier heights of 1.80 eV and 1.67 eV as well as breakdown voltages of 134 V and 180 V were achieved for diodes without and with ITO-ISL, respectively. The surface area of the IBS-Ga2O3 film acted as a thin dielectric layer and, together with the preliminary wet etching, provided low leakage currents and relatively high Schottky barrier heights. Diodes with a Schottky barrier based on a Ni/IBS-deposited Ga2O3 film contact were demonstrated for the first time

Effect of ambient humidity on the electrical conductivity of polymorphic Ga2O3 structures

The effect of ambient humidity on the electrical conductivity of α-Ga2O3 and α-Ga2O3/ε-Ga2O3 is investigated. Polymorphic epitaxial Ga2O3 layers are deposited by the method of chloride vapor-phase epitaxy on sapphire substrates. The contacts are made of Pt and Pt/Ti. It is discovered that the I–V characteristics of the Pt/α-Ga2O3/Pt and Pt/Ti/α-Ga2O3/ε-Ga2O3/Ti/Pt structures have a high sensitivity to atmospheric humidity in the temperature range of 25–100°C. It is found that the effect of water vapor on the I–V characteristics is reversible, and the most significant current changes in the samples are observed at a relative humidity of RH ≥ 60%. As the temperature rises, the effect of atmospheric humidity on the I–V characteristics decreases and disappears at temperatures of T > 100°C. The experimental results obtained are explained within the framework of the Grotthuss mechanism

Effect of oxygen on the Gas-sensitive properties of α-Ga2O3/ε-Ga2O3 structures

Miniature O2 sensors with low energy consumption are of practical interest for the chemical and metallurgical industries, development of systems for analyzing the performance of internal combustion engines and as functional elements of artificial lung ventilation devices. The requirements for miniaturization, high sensitivity, speed and relative cheapness are satisfied by O2 sensors based on β-Ga2O3. The chemical and thermal stability of β-Ga2O3 allows developing gas sensors with extremely high operating temperatures of 400-1100 °C ensuring high reproducibility of their characteristics and high speed of operation. In turn, the high operating temperatures of O2 β-Ga2O3 sensors are their drawback causing high energy consumption

Impact of Cr2O3 additives on the gas-sensitive properties of β-Ga2O3 thin films to oxygen, hydrogen, carbon monoxide, and toluene vapors

High-temperature β-Ga2O3:Cr2O3-based sensors sensitive to oxygen- and hydrogen-containing gases have been developed and studied. Magnetron cosputtering is the method of choice for the thin film synthesis as an industry-compatible technique. The composition-structure-properties relationship has been revealed. An introduction of 0.04–0.14 wt. % Cr leads to a significant increase in the response of the O2 sensors over the temperature range 250–400 °C. The highest response in the above-mentioned temperature range has been achieved for a Cr addition of 0.14 wt. %. An increase in the Cr content from 0.04 to 0.22 wt. % leads to a decrease in the β-Ga2O3-based sensors’ response time, especially for low O2 concentrations (≤10 vol. %). Reliable control of the β-Ga2O3:Cr2O3-based sensors’ selectivity to industry-relevant reducing gases—hydrogen, carbon monoxide, and toluene—is demonstrated. β-Ga2O3 films with a Cr incorporation content of 0.04 and 0.06 wt. % have a high response to toluene at operating temperatures 300–500 °C, while the films with 0.14 and 0.22 wt. % Cr have a high response to H2 in the range 400–500 °C. Regardless of the Cr content in β-Ga2O3 thin films, all sensors considered demonstrate a weak response to CO within the operating temperature range 250–500 °C. The results attained are of certain technological importance, i.e., in terms of the development of cost-effective methods for the synthesis of materials and systems for monitoring and control of industry-relevant gases for an environmentally friendly and sustainable growt

Electrical properties of α-Ga2O3 films grown by halide vapor phase epitaxy on sapphire with α-Cr2O3 buffers

We report on growth and electrical properties of α-Ga2O3 films prepared by halide vapor phase epitaxy (HVPE) at 500 °C on α-Cr2O3 buffers predeposited on sapphire by magnetron sputtering. The α-Cr2O3 buffers showed a wide microcathodoluminescence (MCL) peak near 350 nm corresponding to the α-Cr2O3 bandgap and a sharp MCL line near 700 nm due to the Cr+ intracenter transition. Ohmic contacts to Cr2O3 were made with both Ti/Au or Ni, producing linear current–voltage (I–V) characteristics over a wide temperature range with an activation energy of conductivity of ∼75 meV. The sign of thermoelectric power indicated p-type conductivity of the buffers. Sn-doped, 2-μm-thick α-Ga2O3 films prepared on this buffer by HVPE showed donor ionization energies of 0.2–0.25 eV, while undoped films were resistive with the Fermi level pinned at EC of 0.3 eV. The I–V and capacitance–voltage (C–V) characteristics of Ni Schottky diodes on Sn-doped samples using a Cr2O3 buffer indicated the presence of two face-to-face junctions, one between n-Ga2O3 and p-Cr2O3, the other due to the Ni Schottky diode with n-Ga2O3. The spectral dependence of the photocurrent measured on the structure showed the presence of three major deep traps with optical ionization thresholds near 1.3, 2, and 2.8 eV. Photoinduced current transient spectroscopy spectra of the structures were dominated by deep traps with an ionization energy of 0.95 eV. These experiments suggest another pathway to obtain p–n heterojunctions in the α-Ga2O3 system