MORPHOLOGICAL EVOLUTION, GROWTH MECHANISM AND STRUCTURAL PHASE TRANSFORMATION OF ELO GaN NANOSTRUCTURES ON GaAs (001)

Abstract

Epitaxial lateral overgrown (ELO) cubic-phase gallium nitride (c-GaN) films with a selective area growth method were grown on the [100], [1-10] and [110] mask-stripe patterned GaAs (001) substrates by metalorganic vapor phase epitaxy. The growth morphologies of ELO c-GaN films for each mask-stripe direction were investigated by scanning electron microscope (SEM). The results show that c-GaN films on [100] mask stripe pattern exhibited unidentified sidewall facets, on [1-10] mask stripe pattern demonstrated the dominant (113) side wall facets and, finally, on [1-10] mask stripe pattern revealed dominant (111) sidewall facets. Confocal Raman microscope was an instrument to investigate crystal structure that cubic or hexagonal phases on top and sidewall facet of c-GaN films in the specific area of 2 µm in diameter. The structural phase transformation in the ELO c-GaN films was study by varying growth time. High resolution X-ray diffraction analysis was performed to investigate crystal structures and crystal quality of the ELO c-GaN films for each mask stripe direction. Hexagonal phase inclusion was calculated from the integrated X-ray intensities ratio between c-GaN (002) and h-GaN (10-11) reflections extracted from the reciprocal space mappings. Based on our results, normally cubic phase structure has dominant on the (113) sidewall facets and hexagonal phase structure has dominant on the (111) sidewall facets. However, the growth time is not the only parameter that effects on structural phase transformation. Selective area growth with controlled mask fill-factor (FF) is another important parameter to control structural phase transformation. With the suitable mask fill factor (FF >0.7), ELO c-GaN for the [110] mask stripe direction on GaAs (001) showed a good crystal quality and very high cubic phase quantity.