HVPE growth of Si-doped β -Ga2O3 on sapphire: Influence of substrate offcut on structural and electrical properties

In this work, Si-doped β-Ga2O3 films were heteroepitaxially grown on sapphire substrates using halide vapor phase epitaxy (HVPE). The influence of sapphire offcut on growth kinetics, surface morphology, crystalline quality, and electrical transport properties was systematically investigated. Growth kinetics studies revealed a strong dependence of deposition rate on HCl flow, growth pressure, and Ga-source-to-substrate distance, with growth rates reaching up to 30 μm/h. Increasing the sapphire offcut angle from 0° to 8° promoted a transition from multidirectional growth to highly aligned terrace-dominated surfaces, reducing the surface roughness from 14.69 to 2.74 nm. The improved surface morphology was accompanied by enhanced crystalline quality, with phase-pure (2¯01)-oriented β-Ga2O3 growth and a reduction in the rocking-curve full width at half maximum from 994 arc sec (0°) to 414 arc sec (6°). Electrical characterization of films grown on 6° offcut sapphire substrates at growth rates ranging from 0.67 to 7.30 μm/h yielded carrier concentrations ranging from 1.0 × 1017 to 3.4 × 1018 cm−3. A maximum room-temperature Hall mobility of 100 cm2/V s at a carrier concentration of 1.0 × 1017 cm−3 and a peak low-temperature mobility of 405 cm2/V s at 88 K were achieved for a 5.9-μm-thick film grown at 1.97 μm/h, representing the highest reported room- and low-temperature mobilities for HVPE-grown β-Ga2O3 on a sapphire substrate. Analysis of the temperature-dependent transport characteristics yielded donor activation energies of 35 and 90 meV together with a low acceptor concentration of 3 × 1015 cm−3, consistent with the improved crystalline quality achieved on the offcut sapphire substrates. These results demonstrate that HVPE is capable of producing high-quality β-Ga2O3 heteroepitaxial layers with good crystalline quality and carrier transport characteristics, providing a promising pathway for scalable β-Ga2O3 epitaxy on low-cost foreign substrates.