The oxide vapor phase epitaxy (OVPE) method enables the fabrication of low-resistivity GaN crystals. However, polycrystal formation is detrimental to the growth of thick GaN crystals at the high growth rate by the OVPE method. In this study, we focused on H2O additive under the high-rate and high-temperature growth condition to suppress generation of Ga droplet, the origin of polycrystalline GaN. The polycrystal density dramatically decreased by adding H2O, which can convert Ga droplet into Ga2O vapor. We obtained a 431 μm thick OVPE-GaN layer at 108 μm h−1, which is the highest value in GaN crystals grown by the OVPE method.

The oxide vapor phase epitaxy method is expected to be a useful technique for bulk GaN growth, because it allows long-term growth without producing a solid byproduct. However, thick GaN crystals have not been realized due to the growth inhibition caused by polycrystal formation resulting from high H2O partial pressure. In this study, we formed GaN crystals with CH4 gas to decrease the H2O partial pressure in a growth zone by the reaction of CH4 with H2O to produce CO and H2. As a result, H2O partial pressure decreased with increasing CH4 flow rate, and GaN layers could be grown without decrease of growth rate or degradation of the crystalline qualities at a flow rate of 50–100 sccm of CH4 gas. Furthermore, we obtained high crystalline 400-um thick GaN crystals after a growth period of 10 h.

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