Nitrogen radical densities during GaN growth by molecular beam epitaxy, plasma-assisted metalorganic chemical vapor deposition, and conventional metalorganic chemical vapor deposition

N-radical densities during GaN growth were numerically estimated from the recombination rates of the radicals. In MBE, the lifetime of radicals is so long that almost all radicals effused from a radical source are supplied to a surface. At pressures of 10-100 Pa where plasma-assisted MOCVD is performed, the lifetime of the radicals is of the same order as the flight time of the radicals from the cell to a substrate. Because a larger N-2 flow rate is possible, higher radical flux can be achieved more easily than by MBE. In conventional MOCVD, the radicals formed in the vapor phase cannot be the dominant N-source of the GaN growth. Heterogeneous decomposition of NH3, which is preferentially adsorbed by an electron acceptor (Ga atom), is the dominant reaction path to create N atoms for GaN growth. (C) 1996 Elsevier Science Ltd.