Synthesis of GaN bulk crystals and melt growth of GaN layers under nitrogen plasma

Gallium nitrides of wurtzite structure were synthesized by reacting gallium metal with atomic nitrogen in a microwave plasma operating at 200-400 Pa with the power of 420 W and the frequency of 2.45 GHz to avoid high equilibrium pressure. Polycrystalline GaN can be synthesized at low equilibrium pressures of 200-400 Pa and low temperature of 610-700 °C. The yield of polycrystalline GaN was increased by increasing the nitrogen plasma exposure time and reached 96% at 3 h. The growth of GaN layers on (0 0 0 1) sapphire substrate was carried out using the same technique. When the sapphire substrate was placed in the bottom of the BN crucible, GaN layer of about 3 μm was grown on the substrate with the growth rate of 0.5 μm/h. The layer was nearly oriented to (0 0 0 1)GaN∥(0 0 0 1) sapphire. These results indicate that the direct conversion of gallium metal into GaN layer under nitrogen plasma is a useful method.