S2-semipolar GaN grown by HVPE on a non-polar m-plane sapphire: Features of growth and structural, morphological, and optical properties

In our study, we have analysed the effect of a non-polar m-plane of sapphire substrate on the features of HVPE growth as well as the structural, morphological, optical properties, and Raman scattering of the grown single crystal GaN epitaxial film. We found that the chosen technological approach makes it possible to obtain samples of structurally high-quality semipolar gallium nitride with an S2 orientation (11 over line 22) on the m-sapphire. The S2 plane of (11 over line 22) GaN has a polar reversal of phi~ 75? relative to the non-polar (10 over line 10) m-plane of sapphire, as well as an azimuthal tilt. Under the selected conditions of epitaxial growth, the GaN film has the morphology of a stepped terrace formed during the growth of mesa-like crystal islands, and their coalescence determined the observed surface topography. Based on the data analysis obtained by complex structural-spectroscopic methods, the level of residual biaxial stresses and refractive index dispersion were determined, testifying to the high structural and optical quality of the epitaxial film of semipolar GaN. An analysis of Raman spectra revealed the presence of optical anisotropy depending on the polar angle when the heterostructure is rotated around the m axis of the sapphire substrate. Optimisation of the technological methodology may in future lead to a promising approach for the growth of quality GaN structures on large area m-sapphire substrates as optoelectronic devices based on these layers will have excellent characteristics.

Automated summary

In this study, we investigated the effects of a non-polar m-plane sapphire substrate on the properties of HVPE growth and the characteristics of the GaN epitaxial film. We successfully obtained high-quality semipolar GaN samples on the m-sapphire substrate and determined their structural and optical properties. The optimization of the technological methodology may present a promising approach for the growth of high-quality GaN structures on large area m-sapphire substrates.