High-rate OVPE-GaN growth by the suppression of polycrystal formation with additional H₂O vapor in a high-temperature condition

Abstract

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.

High-rate OVPE-GaN crystal growth at a very high temperature of 1300 °C

“…4(b) and 4(c), a 478 μm thick OVPE-GaN layer was obtained for 2.5 h growth (growth rate: 192 μm h −1 ), which was the higher value than that of the previous study, 108 μm h −1 . 21) To confirm that the condition of high-temperature and high-rate growth did not cause deterioration of the crystal quality, we evaluated the radius of the lattice curvature of the c-plane (Rc), XRC-FWHM values, the lattice constant, the TDD, carrier concentration, and resistivity of the freestanding substrate fabricated in this study. By polishing the front and back surfaces of the 478 μm thick OVPE-GaN crystal, we fabricated the 300 μm thick free-standing OVPE-GaN substrate.…”

“…In the previous study, we attempted the high-temperature growth at 1250 °C and succeeded in the suppression of the polycrystal formation at about 100 μm h −1 , and fabricated thick OVPE-GaN layers. 21,22) Thermodynamic calculation predicted that the high-temperature growth condition reduced the nucleation frequency and the Ga 2 O 3 activity in the OVPE-GaN crystal, 21) which is effective in suppressing the polycrystal formation. However, at a further higher growth rate of about 200 μm h −1 , much polycrystalline GaN was generated on the substrate even under the previous growth conditions at 1250 °C.…”

“…For comparison, we plotted data from the previous studies that reported the growth of thick OVPE-GaN layers at 1200 °C20) and 1250 °C. 21) When the polycrystalline GaN formed on the substrate surface, the growth rate slowed down. On the other hand, when the polycrystal formation was suppressed, the growth thickness increased linearly with the growth period.…”