Abstract:

The surface and growth conditions for the formation of textured polycrystalline bulk gallium nitride (GaN) crystals under nitrogen (N2) reactive plasma were investigated. Langmuir probe measurements were used to determine the electron density values near the Ga surface at different target locations and ranged from (6–16)×1010/cm2. Optical spectroscopy measurements showed reactive gallium (Ga) and nitrogen species present in the plasma. When the target was bombarded with highly energetic ions, peaks of sputtered Ga at 403 and 417 nm wavelengths were observed in the optical spectroscopy measurements. The top Ga surface showed increased roughening and the resulting crystals were of poor crystalline quality, with fresh Ga leftovers. Smoother crystals were formed when the Ga target was shielded from the direct bombardment of highly energetic N2 plasma, with no sputtered Ga peaks observed during the bombardment. X-ray diffraction (XRD) analysis results revealed well-oriented crystals at the (0002) reflection of GaN. This proved that the shielding of highly energetic ions to decrease roughening of the surface and allowing more neutrals for the reaction were effective in forming well-oriented bulk GaN crystals.