Determination of the critical layer thickness in the InGaN/GaN heterostructures

We present an approach to determine the critical layer thickness in the ${\mathrm{In}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N/GaN}$ heterostructure based on the observed change in the photoluminescence emission as the ${\mathrm{In}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N}$ film thickness increases. From the photoluminescence data, we identify the critical layer thickness as the thickness where a transition occurs from the strained to unstrained condition, which is accompanied by the appearance of deep level emission and a drop in band edge photoluminescence intensity. The optical data that indicate the onset of critical layer thickness, was also confirmed by the changes in ${\mathrm{In}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N}$ surface morphology with thickness, and is consistent with x-ray diffraction measurements.