Effect of nitridation on the growth of GaN on ZrB₂(0001)/Si(111) by molecular-beam epitaxy

The effect of nitridation on the epitaxial growth of GaN on lattice-matched ZrB₂(0001) films prepared ex situ and in situ was studied using an ultrahigh-vacuum molecular-beam epitaxy (MBE)-scanning probe microscopy system. The growth of GaN was carried out by rf-plasma-assisted MBE, and epitaxy of wurtzite GaN was observed on both ex situ and in situ prepared ZrB₂ samples. The polarity was found to be consistently N-polar regardless of the samples, based on the observation of a series of N-polar Ga-rich reconstructions: (3 × 3), (6 × 6), and c(6 × 12). The nitridation of ZrB₂ film was conducted by exposing it to active nitrogen and well-ordered hexagonal-BN (h-BN) formation was observed when the annealing temperature was above 900 °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.