Conductivity of Ga$_{2}$O$_{3}$–GaAs heterojunctions

The effect of annealing in argon at temperatures of $T_{\operatorname{an}}$ = 700–900$^\circ$C on the I–V characteristics of metal–Ga$_{2}$O$_{3}$–GaAs structures is investigated. Samples are prepared by the thermal deposition of Ga$_2$O$_3$ powder onto GaAs wafers with a donor concentration of $N_d$ = 2 $\times$ 10$^{16}$ cm$^{-3}$. To measure the I–V characteristics, V/Ni metal electrodes are deposited: the upper electrode (gate) is formed on the Ga$_2$O$_3$ film through masks with an area of $S_k$ = 1.04 $\times$ 10$^{-2}$ cm$^2$ and the lower electrode in the form of a continuous metallic film is deposited onto GaAs. After annealing in argon at $T_{\operatorname{an}}\ge$ 700$^\circ$C, the Ga$_{2}$O$_{3}$–$n$-GaAs structures acquire the properties of isotype $n$-heterojunctions. It is demonstrated that the conductivity of the structures at positive gate potentials is determined by the thermionic emission from GaAs to Ga$_2$O$_3$. Under negative biases, current growth with an increase in the voltage and temperature is caused by field-assisted thermal emission in gallium arsenide. In the range of high electric fields, electron phonon-assisted tunneling through the top of the potential barrier is dominant. High-temperature annealing does not change the electron density in the oxide film, but affects the energy density of surface states at the GaAs–Ga$_2$O$_3$ interface.