Influence of the substrate material on the properties of gallium-oxide films and gallium-oxide-based structures

The influence of the substrate material on the properties of gallium-oxide films formed on sapphire and $n(p)$-GaAs semiconductor wafers by high-frequency magnetron-assisted deposition is studied. The films grown on insulating substrates, as a rule, are of the n type and possess a high resistance. The increase in their conductivity with temperature is defined by the ionization of deep donor centers, whose energy is (0.98 $\pm$ 0.02) eV below the bottom of the conduction band. Gallium-oxide films grown on single-crystal GaAs layers are of the $n$ type as well, irrespective of the conductivity type of the semiconductor substrates. However, the conductance of such films is noticeably higher, which is attributed to the possible diffusion of uncontrollable impurities from the semiconductor into the growing gallium-oxide layer. The electrical characteristics of Ga$_2$O$_3$– semiconductor structures are defined to a larger extent by the properties of the oxide–semiconductor interface than by the properties of the contacting materials. In the reverse branch of the current–voltage characteristics of Ga$_2$O$_3$/$p$-GaAs samples before annealing, a region of $N$-type negative resistance is observed. After annealing of the gallium-oxide films at 900$^{\circ}$C (30 min), the conductance of the structures corresponds to the current–voltage characteristic of a backward diode.