Observation of ring defects in high indium content InGaN/GaN MQW

We report here on the observation of GaN islands in the barrier layer of high In content MQW structures which are surrounded by nanometer scale V-defects. These defects form nearly hexagonal rings when InGaN based multiquantum well (MQW) active layers are deposited under hydrogen free conditions or at growth temperatures below 800 deg C. Mechanical properties of the areas enclosed and outside of the ring defects as examined by ultrasonic force microscopy (UFM) show small variation in the material composition. Chemical etching of the MQW structure showed a slight difference in the etch rate of the ring defect against its surrounding regions, ruling out the possibility of growth of N-polar GaN in a Ga-polar GaN matrix. We did not observe formation of any ring defects at higher growth temperatures above 800 deg or when hydrogen is added.