Growth of GaN on a‐plane sapphire: in‐plane epitaxial relationships and lattice parameters

Abstract

We have studied GaN films grown on a-plane sapphire substrates by both hydride vapor phase epitaxy (HVPE) and metalorganic vapor phase epitaxy (MOVPE). The in-plane orientation relationships between the epitaxial films and the substrate are determined to be [11][12][13][14][15][16][17][18][19][20] 1 Introduction Although the c-plane sapphire is known to be the most commonly used substrate in the GaN device technology, the a-plane sapphire is actually preferable for some applications like edge emitting lasers due to the alignment of the easy cleavage planes of both GaN film and the substrate [1]. Recently, a significant improvement of the properties of the GaN films grown on a-sapphire was reported, however, the understanding of the growth modes of the GaN films on this specific substrate orientation is still far from complete. In particular, the epitaxial relationships between the substrate and the films are of importance for the knowledge of the specific epitaxy rules that can allow a controllable and optimised growth of device structures. Although there are several reports on this subject [2-6], the results scatter and an explanation for the observed difference is still missing. On the other hand it is clear that the different lattice matches between the layer and substrate will contribute to the strain anisotropy, and although it is a well known phenomenon in GaN films grown on a-sapphire (mainly because of the different thermal coefficients in c-and a-directions of sapphire) its effect on the in-plane lattice parameters is not studied yet.In order to clarify that, in this work we perform a thorough study of GaN films grown on a-plane sapphire substrates by two different techniques, HVPE and MOVPE.

Analysis of polarization‐dependent photoreflectance studies for c ‐plane GaN films grown on a ‐plane sapphire

“…This behavior was reported for HVPE-grown material in [16] and for MBE-grown material employing a low-temperature GaN buffer layer in [17]. In the second orientation, the ), which was found in samples grown by MOVPE [16] and is also present in the structures investigated here. An illustration of this orientation is depicted in Fig.…”

Growth of m ‐GaN layers by epitaxial lateral overgrowth from sapphire sidewalls

“…1. Here, the orientation of the GaN layer on the a-plane sapphire is described when the buffer layer is deposited [25]. In the case of a GaN layer grown on c-plane sapphire, the m-axis of GaN corresponds to the a-axis of sapphire.…”

Control of in‐plane epitaxial relationship of c ‐plane AlN layers grown on a ‐plane sapphire substrates by hydride vapor phase epitaxy

“…However, the AlN layers have higher dislocation densities than bulk AlN crystals produced by sublimation-recondensation growth [6,7]. Using an a-plane sapphire instead of a c-plane sapphire as the starting substrate is promising for reducing the threading dislocation density of the AlN layer since it has an in-plane epitaxial relationship with a small lattice mismatch [8]. However, there have been few studies of AlN growth on aplane sapphire [9,10].…”