Effect of defects on strain state in nonpolar a-plane GaN

We have investigated the influence of basal stacking fault (BSF) and impurity related defect on the strain state of a-plane GaN epilayers. Four a-plane GaN epilayers were grown on r-plane sapphire using different growth strategies by metalorganic chemical vapor deposition. It is found that with a growing number of stacking fault, both the anisotropic in-plane strain and compressive out-plane strain along c-axis are relieved. Epitaxial lateral overgrowth with a TiN interlayer is an effective way to relieve in-plane strain and reduce BSF density. The extrapolated lattice parameters free of biaxial strain increase with the normalized yellow luminescence intensity. Hydrostatic strain induced by impurity-related defects is the possible cause of this phenomenon.

► Anisotropic strain in a-plane GaN can be relaxed with increasing number of BSF.
► Impurity related defect causes hydrostatic strain.
► Hydrostatic strain is secondary to biaxial one.
► Higher the impurity level is, the larger lattice parameter presents.