Sub-μm features patterned with laser interference lithography for the epitaxial lateral overgrowth of α-Ga2O3 via mist chemical vapor deposition

Abstract

The low growth rate of mist chemical vapor deposition normally requires a long growth time to achieve coalescence in the epitaxial lateral overgrowth of α-Ga2O3 thin films on sapphire substrates. To address this issue, sub-μm features were patterned using laser interference lithography. Periodical stripes with a ∼590-nm pitch allowed the overgrowth of crack-free, void-free, and continuous thin films, while typical growth conditions using a low carrier gas flow rate and a low Ga precursor concentration were maintained. Coalescence was achieved even with a short growth time of <30 min and a low film thickness of <500 nm. Transmittance and x-ray diffraction spectra show that the film was predominantly in α-phase. Transmission electron microscopy (TEM) images reveal cup-top-like α-Ga2O3 regions of low dislocation density on the SiOx mask. Selected area electron diffraction and high-resolution TEM analyses confirm that an α-Ga2O3 layer was formed even on the top of the SiOx mask. Interestingly, the dislocations formed on the window areas did not bend toward the center of the masks; rather, a dislocation bending outward from the center was observed. This suggests the occurrence of early coalescence and/or atomic rearrangement.