Time of flight mass spectroscopy of recoiled ions studies of surface kinetics and growth peculiarities during gas source molecular beam epitaxy of GaN

High growth rate GaN thin films were successfully grown by gas source molec ular beam epitaxy and studied in situ by time of flight mass spectroscopy o f recoiled ions (TOF-MSRI) and reflection high energy electron diffraction (RHEED). We show that TOF-MSRI allows for in situ monitoring and control of sapphire surface chemistry and its nitridation. In the latter case, TOF-MS RI is more sensitive to the surface changes during nitridation than RHEED. Using both RHEED and TOF-MSRI, growth of low-temperature GaN buffer layers was monitored, and their recrystallization and island-like nature were demo nstrated. A model describing the probable growth mechanism for gas source m olecular beam epitaxy of GaN is suggested. The model explains both the chem ical dissociation of ammonia at low temperature and the origin of Ga to N T OF-MSRI peak ratio changes for various Ga and ammonia fluxes. High-resoluti on transmission electron microscopy studies confirm that GaN films grown wi th a buffer layer have excellent structural quality without any evidence of interfacial defects. Those without a buffer layer are highly defective. (C ) 1999 American Institute of Physics. [S0021-8979(99)07502-7].