Properties of Resistive Structures Based on Gallium Oxide Polymorphic Phases
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ties of Resistive Structures Based on Gallium Oxide Polymorphic Phases V. M. Kalyginaa*, V. I. Nikolaevb, A. V. Almaeva, A. V. Tsymbalova, Yu. S. Petrovaa, I. A. Pechnikovc, and P. N. Butenkoc a
Tomsk State University, Tomsk, 634050 Russia Perfect Crystals LLC, St. Petersburg, 194064 Russia c Ioffe Physical Technical Institute, Russian Academy of Sciences, St. Petersburg, 194021 Russia *e-mail: [email protected] b
Received April 16, 2020; revised May 30, 2020; accepted May 30, 2020
Abstract—The effect of UV radiation and a strong electric field on the current–voltage characteristics of resistive structures based on polymorphic gallium oxide (Ga2O3) films is discussed. Ga2O3 films were deposited by the method of halide vapor phase epitaxy (HVPE) on smooth and patterned sapphire substrates with a baseline orientation (0001). α-Ga2O3 films grow on smooth substrates, and gallium oxide films containing α and ε phases grow on patterned ones. A switching effect was detected in the metal/Ga2O3/metal structures based on two-phase films. When exposed to radiation with λ = 254 nm and a strong electric field, the structures pass from a low resistive state to a high resistive state. Keywords: gallium oxide, films, HVPE, polymorphism, ultraviolet, solar-blind structures. DOI: 10.1134/S1063785020090060
Gallium oxide is a binary semiconductor compound that can be crystallized in five modifications: α, β, γ, δ, and ε [1–3]. Due to its physicochemical properties, this wide bandgap semiconductor is of practical interest for creating solar-blind UV photodetectors, high-voltage devices, gas sensors, transparent electrodes, etc. [4]. At the moment, β-Ga2O3 (Eg ~ 4.8 eV) is the most studied because of its high thermal and chemical stability [5–7]. β-Ga2O3 has a monoclinic lattice, the parameters of which have a large mismatch with other semiconductor crystals, such as Al2O3, Si, SiC, etc. This complicates the growth of high-quality β-Ga2O3 layers, including epitaxial ones, on these substrates [8]. The α-Ga2O3 polymorph, which has a corundum structure and is characterized by a small difference in the lattice constants with sapphire (Δc/c = 3.3% and Δa/a = 4.5%), crystallizes in layers of high structural perfection on its surface [9]. Note that α-Ga2O3 has the largest bandgap (5.1– 5.3 eV) [10], which makes it possible to consider it promising for design of solar-blind detectors in the deep UV range. The epitaxial films of tin-doped gallium oxide of ntype conductivity were grown by the method of halide vapor phase epitaxy (HVPE) in a reactor of LLC Perfect Crystals. For deposition, smooth and patterned sapphire substrates (PSSs) with (0001) orientation were used. In a single growth process, pure α-Ga2O3
phase layers were obtained on smooth substrates, and two-phase layers with columnar α-Ga2O3/ε-Ga2O3 structures were obtained on patterned ones [11, 12]. The purpose of the work was to study the features of the electric and photoelectric characteristics of thin gallium oxide layers depending on the substrate structure. To measure electric c
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