Siam Physics Congress 2015

Strain modification of MOVPE grown cubic GaN on GaAs (001) with GaN/AlGaN multi-interface buffer layer

21 May 2015, 13:00

3h 30m

Board: MNA-69

Poster presentation Material Physics, Nanoscale Physics and Nanotechnology Poster-3

Speaker

Mr Kunpot Mopoung (Nanoscience and technology, Graduate school, Chulalongkorn University, Bangkok, THAILAND 10330)

Description

We have investigated cubic GaN (c-GaN) layers on GaAs (001) substrates by using high resolution X-ray diffraction (HRXRD) to verify strain modification due to a use of the GaN/AlGaN multi-interface buffer layer. To examine lattice parameters and residual strain, both a symmetric (002) and an asymmetric (113) reflections were performed using 2θ-ω mode HRXRD for different types of c-GaN samples. Cross-sectional scanning electron microscopy (SEM) images were used to verily thicknesses of the buffer layer and the GaN top layers. It is found that the fully relaxed lattice constant of c-GaN was determined to be closer to the values of a hypothetical perfect crystal (4.503 Å). Besides, a type of buffer layers remarkably effects on an in-plane strain (ε$_{\textrm{//}}$), which is caused by a combination of a large lattice-mismatch and a difference of thermal expansion coefficients between GaAs and c-GaN. The c-GaN layers with the AlGaN/GaN structure exhibited a tensile strain. While, the c-GaN layers on the conventional low-temperature grown c-GaN buffer layer were examined to be under compressive strain. With the use of GaN/AlGaN as a buffer layer, residual strain in c-GaN thick layers were adjusted to be a tensile strain. Based on our results, we interpreted this strain modification as a competition between the lattice-mismatch and thermal mismatch stresses. This indicates that the relief of strains in the c-GaN layers has a complicated dependence on a type of buffer layers, especially for multi-interface buffer layer.