The Origin of Enhanced Crystal Quality of Heteroepitaxially Grown (-201) β-Ga 2 O 3 on Off-cut Sapphire Substrate by LI-MOCVD

Monoclinic gallium oxide (β-Ga2O3) is an ultrawide bandgap (UWBG) semiconductor material that has attracted significant attention due to its exceptional material properties, rendering it well-suited for a range of device applications, including predominantly power electronic devices but also gas sensors, UV photodetectors or nonlinear optical devices. To address the high cost of native substrates and excessive self-heating of homoepitaxial Ga2O3devices, Ga2O3is often grown heteroepitaxially, for example on sapphire, SiC, Si etc. In the case of foreign substrates exhibiting hexagonal surface symmetry, this can result in the formation of rotational domains (RDs) within the β-Ga2O3layer. This phenomenon is known to compromise the crystal quality and impair the electric properties. To address this issue, the present study investigated the growth of (-201) β-Ga2O3on vicinal c-plane sapphire substrates using the liquid-injection MOCVD technique. Multiple sapphire off-cuts (0°, 4°, 6°, 8°, 10°) towards a-plane were used and explored. A comprehensive structural, electrical, and optical characterisation of grown layers was conducted using a range of analytical techniques, including X-ray diffraction (XRD), atomic force microscopy, van der Pauw and Hall-effect measurements, and room temperature photoluminescence spectroscopy. While the RDs were not suppressed, the quality of the β-Ga2O3crystal was greatly influenced by the use of off-cut substrates..