ABSTRACT
This chapter discusses the advantages of using ammonia as the nitrogen source for molecular beam epitaxy (MBE) growth. It describes the growth of AlGaN/Gallium Nitride (GaN) high-electron-mobility transistors (HEMT) heterostructures on GaN-on-sapphire templates, freestanding GaN, and foreign substrates like silicon and silicon carbide. To evaluate the potentialities of these structures, test devices including transmission line model (TLM) and isolation patterns, diodes, and transistors have been fabricated by photolithography. The transistor leakage on hexagonal SiC better scales with buffer leakage, indicating a more stable behavior with respect to the electric fields and the self-heating. With a growth temperature intermediate between power amplifier-MBE and metalorganic vapor phase epitaxy, ammonia-MBE presents the advantage of combining a simple N-rich growth regime with acceptable growth rate and uniformity. The degradation of metalorganic chemical vapor deposition-grown devices is similar to that of ammonia-MBE-grown devices, showing that ammonia favors antisite-related defects themselves passivated by hydrogen.
