Hydrogen and nitrogen ambient effects on epitaxial lateral overgrowth (ELO) of GaN via metalorganic vapor-phase epitaxy (MOVPE)

Abstract

Ambient gas effect on the epitaxial lateral overgrowth (ELO) of GaN via metalorganic vapor-phase epitaxy (MOVPE) on a MOVPE-grown GaN (0001) / sapphire (0001) substrate with a SiO2stripe mask has been studied by means of field-emission scanning electron microscopy (SEM) and high-resolution X-ray diffraction (XRD) analysis. Different ambient gases of nitrogen, hydrogen and their mixture (mixture ratio, hydrogen: nitrogen =1:1) affect the lateral overgrowth rate, the surface morphology and the crystalline tilting of ELO-GaN layers. XRD revealed that the ELO-GaN layer on the SiO2mask aligned along the 〈1̄100〉 direction exhibited anisotropic crystalline tilting toward <11̄2 0>. For ELO-GaN growth in nitrogen ambient, the growth rate of the (0001) facet decreases, the lateral overgrowth rate increases and the tilting of the ELO-GaN layer increases, while no smooth surface is obtained, in comparison with ELO-GaN growth in hydrogen ambient. For the mixture ambient, a smooth surface with a fast lateral overgrowth rate is achieved and the dislocation density is not more than 107cm-2, which is comparable to that in hydrogen ambient.