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

Abstract

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‾22) on the m-sapphire. The S2 plane of (11‾22) GaN has a polar reversal of φ ∼ 75° relative to the non-polar (10‾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.