Surface and interface studies of GaN growth on ZrB$_{2}$(0001)/Si(111)

ZrB$_{2}$ is a conductive, reflective, and lattice-matched buffer layer for GaN growth on Si. This study demonstrates the inherent suitability of ZrB$_{2}$ as an ideal buffer layer for growing inversion domain-free GaN films on Si using an UHV MBE-SPM system. Single crystal ZrB$_{2}$ films had been grown on Si(111) by the thermal decomposition of single molecular precursor Zr(BH$_{4})_{4}$. Annealing the film at 800$^{o}$C in UHV was enough to remove the surface oxides and recover the atomically smooth surface. The GaN grown on the oxide-free ZrB$_{2}$ by plasma-assisted MBE was found to be consistently N-polar independent of the growth conditions. The films were insulating and N-polarity was demonstrated by combined \textit{in situ }RHEED and non-contact AFM study. Various interface structures were proposed and as a result of first principles calculations, a single interface structure leading to N-polar GaN growth was found most stable for the wide range of growth conditions. Ref. Y. Yamada-Takamura \textit{et al.,} Phys. Rev. Lett. \textit{in press}.