In situ control of GaN growth by molecular beam epitaxy

Methods to determine GaN surface temperature, surface composition, and growth rates using in situ desorption mass spectroscopy (DMS) and reflection high energy electron diffraction (RHEED) are demonstrated for molecular beam epitaxial growth of GaN using NH₃. Using these methods, the GaN surface temperature, T_s, and GaN growth rates as a function of T_s, Ga flux, and NH₃ flux were obtained. Surface temperatures were determined from DMS and RHEED measurements of the temperature at which Ga condenses on GaN. NH₃-limited and Ga-limited growth regimes are identified and the transition between these regimes is shown to be abrupt. NH₃-limited samples have a weakly reconstructed (2 × 2) RHEED pattern, while Ga-limited samples reveal a transmission pattern. Atomic force microscopy showed that NH₃-limited samples exhibit atomic steps while Ga-limited samples exhibit faceting.