Conducting (Si-doped) aluminum nitride epitaxial films grown by molecular beam epitaxy

摘要

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 varioussemiconductor devices, research on AlN has been limited and n-type conducting AlN has not been reported. The objective of this research was to understand the factors impacting the conductivity of AlN and to control the conductivity of this materialthrough intentional doping. Prior to the intentional doping study, growth of undoped AlN epilayers was investigated. Through careful selection of substrate preparation methods and growth parameters, relatively low-temperature molecular beam epitaxialgrowth of AlN 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°C, AlN films wereinsulating, however, below a growth temperature of 900°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 Gaflux during growth. For instance, conducting, Si-doped, AlN films were grown at a growth temperature of 940°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, epilayers with n-type conductivity values as large as 0.2Ω{sup}(-1)cm{sup}(-1) for AlN and 17Ω{sup}(-1)cm{sup}(-1) for Al{sub}(0.75)Ga{sub}(0.25)N were grown in this work for the first time.