Structural characterization of InGaN/GaN multi-quantum well structures using high-resolution XRD

The structural properties of 10-period In0.15Ga0.85N/GaN multiple quantum wells (MQWs) have been investigated using HRXRD (high-resolution X-ray diffraction). For the samples, the barrier thickness was kept constant, 7.5 nm and the well thicknesses were varied, 1.5, 3.0, 4.5, and 6.0 nm. For the X-ray structural characterization, an omega/2theta-scan and an omega-scan for GaN (00.2) reflection and a reciprocal space mapping (RSM) around the GaN (10.5) lattice point were employed. The average strain for tile MQWs increased as the well thickness increased. Tile MQW, with a 6.0 nm well thickness experienced lattice relaxation and the crystallinity of tile sample was poor compared to that of the other samples. MQWs with well thicknesses of 1.5, 3.0 and 4.5 nm, however, maintained lattice coherency with the GaN epilayers underneath, and the critical well thickness for lattice relaxation of the MQWs used in the study was 6.0 nm. The degree of relaxation along in-plane direction for the lattice relaxed MQW was about 2.8 %.