Growth and Characterization of GaN/InGaN Multiple Quantum Wells on Nanoscale Epitaxial Lateral Overgrown Layers

Abstract

GaN/InGaN multiple quantum wells (MQWs) were fabricated on nanoscale epitaxial lateral overgrown (NELO) GaN layers (type N) by metal−organic chemical vapor deposition using a SiO2 layer with nanometer scale windows as the growth mask. Transmission electron microscopy (TEM) results clearly demonstrate coherent growth of GaN in the window regions while lateral growth is observed over the SiO2 layer. Based on the TEM and atomic force microscopy measurements, we observed substantial reduction in the threading dislocation density for the type N GaN films. Experimental results on electroluminescence (EL) measurement indicate substantial improvement in the EL intensity as well as a 15 nm blue shift in the EL peak wavelength. High resolution X-ray diffraction and reciprocal space mapping characterizations clearly indicate significant reduction in strain generation in the MQWs grown on NELO GaN layers compared to the control samples (type C). Such reduction in strain generation in the MQW gives rise to the reduction in the quantum-confined Stark effect. This is also consistent with the observed blue-shift in the EL peak. Detailed analyses of the optoelectronic properties of the devices indicate significant improvements in the internal quantum efficiency, ηi, and the extraction efficiency, ηe, by as much as 55.8 and 57.3%, respectively, compared to the type C devices. The improvement in ηi is attributed to reductions in both the nonradiative recombination centers and the quantum-confined Stark effect in the type N devices and the improvement in the extraction efficiency is attributed to the texturing of the GaN layer due to the incorporation of the SiO2 layer with nanometer scale windows.