Effect of nitridation on the molecular beam epitaxy growth of GaN on ZrB$_{2}$(0001)/Si(111)

ZrB$_{2}$ is a conductive, reflective, and lattice-matched buffer layer for GaN growth on Si. Here we report the effect of nitridation on the epitaxial growth of GaN on ZrB$_{2}$(0001) films prepared \textit{ex situ} and \textit{in situ}, which was studied using an ultrahigh vacuum molecular beam epitaxy - scanning probe microscopy (MBE-SPM) system. The growth of GaN was carried out by rf-plasma assisted MBE, and epitaxy of wurtzite GaN with N-polarity was observed on both \textit{ex-situ} and \textit{in-situ} prepared ZrB$_{2}$ films. The nitridation of ZrB$_{2}$ films were conducted by exposing them to active nitrogen, and well-ordered hexagonal boron nitride (h-BN) formation was observed when the annealing temperature was above 900$^{o}$C. The partially formed BN layer affected neither the epitaxy nor the polarity of GaN, but when the surface was fully covered with well-ordered h-BN, GaN growth did not occur. The high GaN nucleation selectivity observed between clean and h-BN covered ZrB$_{2}$ suggests the possibility of applying epitaxial lateral overgrowth method, which is known to be difficult in elemental source GaN MBE growth. Ref. Z. T. Wang \textit{et al.,} J. Appl. Phys. 100, 033506 (2006).