Cubic GaN layers were grown on AlGaAs (001) substrates by hydride vapor phase epitaxy (HVPE) method. Nitridation treatment on the surface of AlGaAs substrate is carried out using ammonia gas before the initial stage of GaN crystal growth, and its effect on the resulting crystal quality is investigated. It was found growth parameter such as nitridation temperature of AlGaAs substrate, low temperature GaN buffer layer and interlayer growth condition, V/III ratio and thickness of GaN layer to be critical determinants for the growth of cubic GaN layer.
Nitridation treatment by ammonia gas forms Nitrided layer on AlGaAs substrate surface. The nitrided AlGaAs layer acts as a buffer layer which relaxes strain from difference in lattice constant between AlGaAs and GaN..
In this study, we used multi-buffer (first and second mid-temperature GaN : MT-GaN) layers to obtain cubic GaN films. The first MT-GaN layers were grown at moderate temperature to prevent substrate from thermal etch during high temperature growth. The second MT-GaN layers were used to reduce the hexagonal GaN incorporation in the cubic GaN films. It is demonstrated that a multi buffer layer structure in place of the conventional single buffer layer structure can effectively suppress the hexagonal GaN incorporation. These methods enable us to grow cubic GaN layers on AlGaAs (001) substrates at high temperature (1050 oC).
Surface morphologies and chemical constituents of nitrided AlGaAs layers were characterized with scanning electron microscopy (SEM) and Energy Dispersive X-ray (EDX). For the optical and crystalline characterization of the GaN films, X-ray diffraction (XRD), SEM, Photoluminescence (PL) cathodoluminescence (CL), were carried out.
From the above results, we suggest that HVPE method could be possibly used in the growth of cubic GaN.