Effects of controlled ambidirectional nucleation on the heteroepitaxial growth of m-GaN on m-sapphire

Abstract

We found that m-plane GaN grown on m-plane sapphire nucleates in ambidirections at the initial growth stage, which seriously degrades the surface morphology and the crystallinity of m-GaN films. To avoid the ambidirectional islanding of m-plane GaN, off-cut m-plane sapphire (toward to the [112¯0] direction) substrates were introduced. When the off-angle was small as 1°–2°, the surface step determined the epitaxial orientation of m-GaN islands. Hence, an m-GaN film with a smooth surface and a low-dislocation density was obtained. However, the dislocation component of m-GaN film was increased with increasing of the off angle due to step bunches.

Semipolar and nonpolar GaN epi-films grown on m-sapphire by plasma assisted molecular beam epitaxy

“…Nonpolar (10-10) GaN and semipolar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) GaN epilayers were separately grown on (10-10) m-plane sapphire substrates by Omicron Nanotechnology plasma-assisted MBE system. The initial chemical cleaning procedure was kept same for both the samples.…”

“…7,8 The difficulties in obtaining high-quality nonpolar material lie in the planar anisotropic nature of the growth mode, which is a consequence of the anisotropy of both the lattice mismatch and the adatom diffusion length. 9 Our group has previously reported nonpolar a-plane (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) GaN grown on an r-plane sapphire substrate at different growth temperatures and studied the role of growth temperature in controlling the surface morphology and structural and optical properties of the films. 10 Growth of nonpolar m-GaN on m-sapphire by various techniques such as hydride vapour phase epitaxy (HVPE), 11 metal-organic chemical vapor deposition (MOCVD), 12 and on m-sapphire substrates with slight c-axis miscut 13,14 has been reported earlier but not much study was evident by MBE.…”

“…[1][2][3][4] However, optoelectronic devices made out of the conventional polar orientation are strongly affected by the intrinsic spontaneous and piezoelectric polarization fields. 5,6 Growing GaN on nonpolar orientation such as (10-10) m-plane or (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) a-plane, avoids the polarization effects. Devices grown on these orientations are receiving a lot of focus due to enhanced behavior.…”

“…The effect of nitridation was not fully understood, however, was conjectured that either surface energy or elastic energy played a major role, depending on the nitridation condition. 16 In the present work, nonpolar (10-10) GaN and semipolar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) GaN on m-plane sapphire were grown and their structural and optical properties were studied and compared.…”

Improvement of M-plane GaN thin film grown on pre-annealing β-LiGaO2 (100) substrate

“…The origin of the different growth characteristics of GaN near scratch is not understood yet. We speculate that the surface condition of the annealed LiGaO 2 substrate affects the kinetics of Ga adatom [8] or GaN nucleation growth [9]. Further analysis will be performed by transmission electron microscope.…”