Non-destructive imaging of residual strains in GaN and their effect on optical and electrical properties using correlative light-electron microscopy

We demonstrate a non-destructive approach to understanding the growth modes of a GaN thin film and simultaneously quantify its residual strains and their effect on optical and electrical properties using correlative scanning electron microscopy techniques and Raman microscopy. Coincident strain maps derived from electron backscatter diffraction, cathodoluminescence, and confocal Raman techniques reveal strain variations with similar magnitude and directions, especially in the proximity of dislocations. Correlating confocal Raman imaging with electron channeling contrast imaging suggests that the dislocations organize themselves to form a distinctive pattern as a result of the underlying growth mask, where some of them align along the [0001] growth direction and some are inclined. The methodology presented in this work can be adopted to investigate any heteroepitaxial growth, in particular, those using selective masks on the growth substrates, where the morphology influences the subsequent growth.