Effect of Oxygen on the Gas-Sensitive Properties of α-Ga 2 O 3 /ε-Ga 2 O 3 Structures

Miniature O 2 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 O 2 sensors based on β-Ga 2 O 3 . The chemical and thermal stability of β-Ga 2 O 3 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 O 2 β-Ga 2 O 3 sensors are their drawback causing high energy consumption. Previously, we studied the effect of H 2 on the gas-sensitive properties of the α-Ga 2 O 3 /ε-Ga 2 O 3 structure with Pt contacts grown by the halide vapor phase epitaxy (HVPE) on the patterned sapphire substrates (PSS) [1]. Low operating temperatures, weak dependence of properties on the humidity and control of selectivity by means of voltage changes indicate that the research of α-Ga 2 O 3 /ε-Ga 2 O 3 structures as sensitive elements of gas sensors is promising. We presume that in addition to increasing the applied voltage to the structures, the sensitivity of α-Ga 2 O 3 /ε-Ga 2 O 3 to certain gases, in particular O 2 can be increased by reducing the level of doping with a donor impurity. Thus this work is devoted to research the effect of O 2 on gas-sensitive properties of α-Ga 2 O 3 /ε-Ga 2 O 3 structures doped with Sn. Ga 2 O 3 films were grown by the HVPE in Perfect Crystals LLC. PSS of (0001) orientation and 430 microns in thickness were used as substrates. During the synthesis, the films were doped with Sn. To measure the gas-sensitive properties of the α-Ga 2 O 3 /ε-Ga 2 O 3 structures Pt contacts were formed on their surface. The samples consisted of a mixture of α and ε phases with the orientation (0001). Using scanning and transmission electron microscopy, it was found that the α-phase forms columnar structures at the top of the sapphire cone, and the ε-phase fills the gaps between the columns. The characteristic triangular shape of columnar structures indicates that they consist of α-Ga 2 O 3 with trigonal symmetry. ɛ-Ga 2 O 3 has a grain but not polycrystalline structure taking into account the XRD results. Figure 1 shows the I-U characteristics of α-Ga 2 O 3 /ε-Ga 2 O 3 structures at the exposure of O 2 in