Controlled thin-film deposition of α or β Ga2O3 by ion-beam sputtering

Abstract

The wide bandgap of oxide semiconductors enables solid-state devices with functionalities beyond the reach of technologically more well-established materials such as silicon, germanium, or gallium nitride. These functionalities, among others, include optical transparency paving the way for transparent (opto-)electronics like ultraviolet light emitters or solar-blind detectors as well as large breakdown fields enabling high-power electronic applications. In particular, Ga2O3 is considered as oxide compatible with the nitride III-V materials. As a particular challenge, Ga2O3 may crystallize in different polymorphs. All possess large optical bandgaps beyond 4.8 eV and, thus, are of great interest for such devices. Nowadays, Ga2O3 thin films are prepared by a plethora of different synthesis methods including physical as well as chemical variants, however, reports on a controlled manufacturing process of individual Ga2O3 phases with sputtering techniques are currently scarce. Here, we grow Ga2O3 thin films by ion-beam sputtering on sapphire substrates of different orientation and demonstrate that selective controlled synthesis of different Ga2O3 polymorphs is feasible. The monoclinic β-phase and the corundum-type α-phase are stabilized when deposited on (0001) and (10–10) sapphire substrates, respectively. A stacking rather than a mixture of both phases is observed when thin films of α-phase exceed a certain thickness. Thus, thickness control enables the transition between the two phases. The proposed technique holds promise for ion-beam sputter methods to be employed in Ga2O3-related device build-up.