Morphological study of GaN layers grown on porous silicon

In the present work, we investigate the effect of growth temperature on the crystallinity and morphology of GaN layers grown on porous silicon (PS) by metalorganic vapour phase epitaxy (MOVPE). For this purpose, we use X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM) techniques. XRD analysis show two emerging polycrystalline phases related to the wurtzite and zinc-blende structures. The crystallinity and the dominance of these two phases were found to depend on growth temperature, while one can observe an overall crystallinity improvement at high temperatures. AFM images show a pyramidal growth of the GaN layers. A significant increase of the grain size dimensions from 150 to 800 nm was observed as the temperature rises from 450 to 800 °C. Surface and cross sectional SEM observations of the GaN layers reveal a good surface coverage at 500 °C. A columnar like structure appears at 600 °C. Good agreement was observed between XRD, AFM and SEM results; the temperature dependence of the morphology and crystallinity of GaN grown on PS was clearly evidenced.