| Wurtzite GaN epitaxial films were grown on c-plane sapphire substrate by reactive molecular beam epitaxy (RMBE) process using ammonia gas as the nitrogen source. Compared to conventional MBE processes, in which nitrogen gas is used as the nitrogen source, RMBE process has an advantage of supplying large amounts of ammonia without increasing the chamber pressure excessively. This makes large growth rates (up to 2 ;For the growth of n-type films, a specific ammonia flow rate (or V/III ratio if Ga flux is fixed) was required to obtain films with high electron Hall mobility. X-ray diffraction (XRD), photoluminescence (PL), cross-sectional transmission microscopy (XTEM) and deep level transient spectroscopy (DLTS) results also show consistency with electrical results. For the growth of Mg-doped GaN films, larger ammonia flow rates produced electrically better films. This phenomenon has been accounted for by using a simple Ga vacancy model. Also by carrying out secondary ion mass spectroscopy (SIMS) study for the Mg-doped films, the behavior of Mg and H affected by the ammonia flow rate during the film growth was experimentally investigated for the first time. |
