| AVS 57th International Symposium & Exhibition | |
| Electronic Materials and Processing | Thursday Sessions |
| Session EM+SS-ThM |
| Session: | Nitride Surfaces and Interfaces |
| Presenter: | F. Liu, Carnegie Mellon University |
| Authors: | F. Liu, Carnegie Mellon University L. Huang, Carnegie Mellon University E.A. Preble, Kyma Technologies, Inc. T. Paskova, Kyma Technologies, Inc. K. Evans, Kyma Technologies, Inc. R.F. Davis, Carnegie Mellon University L.M. Porter, Carnegie Mellon University |
| Correspondent: | Click to Email |
Light emitting diodes (LED) with InGaN/GaN multi-quantum wells (MQW) as the active region are now being widely investigated for blue and green light sources. However, InGaN/GaN MQWs grown on sapphire or SiC substrates commonly contain V-shaped defects with densities as high as 109cm-2. These V-defects, which are believed to degrade the internal quantum efficiency of the LED, are remarkably reduced via growth on GaN substrates. In this study, we present a detailed microstructural comparison between In0.2Ga0.8N (3nm)/GaN (8nm) MQWs grown on AlGaN/ SiC (0001) and GaN (0001) substrates via metalorganic chemical vapor deposition at 790oC. The composition was determined by analyses of x-ray diffraction (XRD) and photoluminescence measurements. The microstructure was characterized using a variety of techniques, including transmission electron microscopy (TEM), scanning electron microscopy (SEM), electron channeling contrast imaging (ECCI), and photoelectrochemical (PEC) etching. SEM images revealed that the V-defect density decreased from1 x 1010 cm-2 to 7 x 106 cm-2 in MQWs grown on SiC and GaN substrates, respectively. Cross-sectional TEM images on MQWs grown on SiC substrates indicated that V-defects invariably originated from threading dislocations. To test this hypothesis, we investigated the threading dislocation densities prior to the growth of the MQWs (i.e., in (300-500 nm) GaN films grown on SiC and GaN substrates) via PEC etching and ECCI. The dislocation densities observed in these samples (~6 x 109 cm-2 on SiC; ~4 x 106 cm-2 on GaN) are close to the respective densities of V-defects observed in samples after growth of the MQWs. These results from multiple techniques provide convincing evidence that the dislocation densities in the GaN layer above the substrate determine the densities of V-defects in the MQW. The introduction of dislocations directly from GaN substrates into the homoepitaxial layers is also under investigation using the techniques described herein.