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Gallium oxide (Ga2O3) is positively researched as one of the ultra-wide-bandgap semiconductor materials which are expected to realize cost-effective power devices. To demonstrate device performances, many efforts have been paid on the investigation of crystal growth methods to prepare high-quality drift layers. Among them, halide vapor phase epitaxy (HVPE) has advanced as a capable growth method for n-type conductivity-controlled β-Ga2O3 homoepitaxial layers with a wide range by Si doping. Recently, the fabrication of SBDs and FETs using the β-Ga2O3 homoepitaxial wafers have been reported by many research groups.
In our group, the HVPE growth of Ga2O3 and In2O3 was investigated in an atmospheric pressure system based on thermodynamic analyses, using group-III monochlorides (GaCl and InCl) and oxygen (O2) as precursors and nitrogen (N2) carrier gas. It was found that high-purity single-crystal layers can be grown at around 1000°C. The growth rate was found to be controlled by the input partial pressure of group-III monochloride and reach above 10 μm/h.
In the homoepitaxy on β-Ga2O3(001) substrates, the n-type carrier density in the range 1E15 - 1E18 cm-3 was achieved. For the layer with the carrier density of 3E15 cm-3, the highest room-temperature mobility of 149 cm2/Vs was confirmed. In the heteroepitaxy of c-In2O3(111) on sapphire (0001) substrates, the lowest n-type carrier density of 2.2E16 cm-3 with relatively high mobility of 235 cm2/Vs was achieved. These results indicate that HVPE-grown single-crystal sesquioxides can be applicable to the fabrication of power devices.
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