Microstructural properties of InGaN/GaN light-emitting diode structures with different In content grown by MOCVD

Abstract

The structural and morphological properties of metal-organic chemical vapor deposition (MOCVD)-grown InGaN/GaN light-emitting diode (LED) structures with different In content have been studied by high-resolution X-ray diffraction (HRXRD), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), and Photoluminescence (PL). It is found that the tilt and twist angles, lateral and vertical coherence lengths (CLs) of mosaic blocks, grain size, screw and edge dislocation densities of GaN and AlN layers, and surface roughness monotonically vary with In content. Experimental results show that the mosaic block dimensions for every two layers generally increase with increasing In content, with exception of the lateral CL of the GaN layer, which exhibits an inverse behavior. In this case, the strain values and tilt angles show a decrease accordingly. At the same time, the screw dislocation densities and twist angles of the GaN and AlN layers decrease and increase monotonically, respectively. The edge dislocation density of AlN shows a decreasing behavior, while that of the GaN exhibits an increasing trend. Furthermore, LED structures display an island-like surface structure at a relatively high In composition, in contrast to a well-defined step-terrace structure at a low In composition.