Plasmas for the low-temperature growth of high-quality gan films by molecular beam epitaxy and remote plasma MOCVD

GaN heteroepitaxial growth on sapphire (0001) substrates was carried out by both radio-frequency(rf) remote plasma metalorganic chemical vapor deposition (RP-MOCVD) and molecular beam epitaxy (MBE). A multistep growth process including substrate plasma cleaning and nitridation, buffer growth, its subsequent annealing and epilayer growth was used. In order to achieve a better understanding of the GaN growth, in-situ real time investigation of the surface chemistry is performed for all the steps using the conventional reflection high-energy electron spectroscopy (RHEED) during the MBE process, while laser reflectance interferometry (LRI) and spectroscopic ellipsometry (SE), which do not require UHV conditions, are used for the monitoring of the RP-MOCVD process. The chemistry of the rf N2 plasma sapphire nitridation and its effect on the epilayer growth and quality are discussed in both MBE and RP-MOCVD.