Rapid homoepitaxial growth of (011) β-Ga₂O₃ by HCl-based halide vapor phase epitaxy

We demonstrated rapid homoepitaxial growth on (011) β-Ga₂O₃ substrates using HCl-based halide vapor phase epitaxy (HVPE), in which GaCl was synthesized by reacting metallic Ga with HCl gas, and examined properties of the resulting layer. These were compared with layers grown using Cl₂-based HVPE, where GaCl was produced from Ga and Cl₂. The growth rate on (011) substrates, approximately 60% of that on (001), reached ~14 μm/h, which was 5-7 times higher than those previously reported for Cl₂-based HVPE. Despite this high rate, no polycrystalline grains, sometimes found in Cl₂-based HVPE, were detected. Atomic force microscopy revealed a surface with root-mean-square roughness of 6.5 nm over a 100 × 100 μm² area. In contrast, Nomarski microscopy revealed the presence of pits (~10 μm in diameter at 3.6 μm thickness) with a density of ~3.7 × 10³ cm^-2, a feature not reported for Cl₂-based HVPE. Cross-sectional transmission electron microscopy confirmed the absence of crystal defects or inclusions at the pit bottom. X-ray diffraction 2θ-ω scans and pole figure measurements confirmed that the epitaxial layers were single crystalline, with rocking-curve FWHM values comparable to or smaller than those of the substrate. Secondary ion mass spectrometry revealed a chlorine concentration of 1.7 × 10¹⁵ cm^-3, which was significantly lower than 1.1 × 10¹⁶ cm^-3 measured in the (001) layers. Thus, while the pit issue requires further investigation, HCl-based HVPE enables the rapid growth of low-chlorine (011) β-Ga₂O₃, offering significant potential for cost reduction in high-performance power devices with thick drift layers.