InN growth by plasma-assisted molecular beam epitaxy with indium monolayer insertion

An etching effect of N-plasma on a GaN buffer layer was found in the initial stage of InN growth by plasma-assisted molecular beam epitaxy. We proposed to predeposit 1-2 monolayers (ML) of In (referred to as "In insertion") oil the GaN buffer layer to protect it from etching, thus preserving the flat buffer surface for InN growth. Atomic force microscopy (AFM), high-resolution X-ray diffraction (HRXRD), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL) were carried out to evaluate the GaN buffers and InN films and compare the effect of the In insertion. It has been shown that the In insertion significantly improves the structural quality and optical property of InN. A flatter InN surface, narrower XRD full-width at half-maximum, sharper InN/GaN interface, and stronger PL were observed in optimal samples with 1.8 ML In insertion. The effect of In insertion is discussed in terms of buffer surface protection and enhancement of surface migration of In adatoms.