Wurtzite to zinc-blende phase transition in gallium nitride thin films

The phase transition in gallium nitride (GaN) thin films at room temperature from the thermodynamically stable wurtzite to the metastable zinc-blende structure is studied. The GaN films were grown at room temperature on (100)-oriented silicon substrates by radio-frequency planar magnetron sputtering of a GaN target in pure nitrogen atmosphere. As the nitrogen gas pressure during the film growth is decreased from 30 to 10 mTorr, the crystalline phase of GaN films changed from a hexagonal wurtzite to a cubic zinc-blende structure with (111) crystallographic planes oriented preferentially parallel to the film surface. The mechanisms responsible for the formation of the nonequilibrium cubic zinc-blende GaN phase at room temperature are suggested, in which the impact of the hyperthermal species impinging on the surface of growing films plays a key role in stabilizing the zinc-blende phase of GaN.