Conducting (silicon-doped) aluminum nitride epitaxial films grown by molecular beam epitaxy: Experiment and theory

As a member of the III-V nitride semiconductor family, AlN, which has a direct energy-gap of 6.2eV, has received much attention as a promising material for many applications. However, despite the promising attributes of AlN for various semiconductor devices, research on AlN has been limited and conducting AlN has not been reported.; The objective of this research was to understand the factors impacting the conductivity of AlN (or high Al content AlGaN) and to control the conductivity of this material through intentional doping.; Prior to the intentional doping study, growth of undoped AlN and high Al content AlGaN epilayers was investigated. Through careful selection of substrate preparation methods and growth parameters, relatively-low temperature molecular beam epitaxial growth of AlN and high Al content AlGaN films was established which resulted in insulating material.; Intentional Si doping during epilayer growth was found to result in conducting films under specific growth conditions. Above a growth temperature of 900{dollar}spcirc{dollar}C, AlN films were insulating, however, below a growth temperature of 900{dollar}spcirc{dollar}C, the AlN films were conducting.; The magnitude of the conductivity and the growth temperature range over which conducting AlN films could be grown were strongly influenced by the presence of a Ga flux during growth. For instance, conducting, Si-doped, AlN films were grown at a growth temperature of 940{dollar}spcirc{dollar}C in the presence of a Ga flux while the films were insulating when grown in the absence of a Ga flux at this particular growth temperature. Also, by appropriate selection of the growth parameters, AlN epilayers with conductivity values as large as 17 {dollar}Omegasp{lcub}-1{rcub}{dollar} cm{dollar}sp{lcub}-1{rcub}{dollar} were grown in this work for the first time.; The roles of both growth temperature and Ga adatoms in controlling the conductivity of Si-doped AlN epitaxial films were considered in a model involving non-equilibrium thermodynamics and kinetics and the model was applied to explain the novel experimental observations.