Vapor Phase Epitaxy of Nitride Films

GaN and related compounds are very promising materials for developing short wavelength light emitting devices, such as laser diode (LD) and light emitting diode (LED), high temperature and high power electronics. Commercially used nitride materials have been made by vapor phase epitaxy (VPE), including metalorganic vapor phase epitaxy (MOVPE) and hydride vapor phase epitaxy (HVPE). MOVPE is a widely used technique to fabricate semiconductor films. Its precise control of growth process, ability of handling multi large area wafers, and excellent reproducibility make it valuable in large-scale production of electronic and optoelectronic devices. VPE of nitrides has met several critical materials issues. Firstly, a high vapor pressure of nitrogen leads to the lack of bulk crystal of GaN. People have to use heteroepitaxy technique to produce GaN materials and devices, which makes high-density defects in GaN epilayers. Secondly, the high bonding energy of GaN and high stability of NH₃ require a high growth temperature. The high nitrogen vapor pressure at high growth temperature requires enhanced local precursor densities. Additionally, the growth chemistry of VPE of nitride materials is very complicated. Parasitic chemical reactions take place during the VPE growth and degrade the material quality. Finally, the physical process of VPE growth has not been well understood. Optimized production of nitride material is predicated on an understanding of how the film properties are affected by the initial processing sequence. Heteroepitaxy of nitrides is strongly influenced by the initial nucleation and growth sequence.