Structural and Optical Characteristics of Laterally Overgrown GaN Pyramids on (111) Si Substrate
- PDF / 1,654,158 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 52 Downloads / 212 Views
STRUCTURAL AND OPTICAL CHARACTERISTICS OF LATERALLY OVERGROWN GaN PYRAMIDS ON (111) Si SUBSTRATE Yong-Hoon Cho1, H. M. Kim2, T. W. Kang2, J. J. Song3, and W. Yang4 1 Department of Physics, Chungbuk National University, Cheongju 361-763, Korea 2 Quantum-Functional Semiconductor Research Center and Department of Physics, Dongguk University, Seoul 100-715, Korea 3 Center for Laser and Photonics Research and Department of Physics, Oklahoma State University, Stillwater, OK 74078 4 Honeywell Technology Center, 12001 State Highway 55, Plymouth, MN 55441
ABSTRACT Structural and optical characteristics of laterally overgrown GaN pyramids on a (111) Si substrate were investigated by scanning electron microscopy, transmission electron microscopy (TEM), and cathodoluminescence (CL) microscopy and spectroscopy. Cross-sectional TEM images revealed that the threading dislocation density over the window openings is very high, but gradually decreases with increasing GaN thickness, and that dislocations observed over the mask are parallel to the mask interface. Cross-sectional-view CL images taken at different emission wavelengths clearly showed significant differences between the overgrown areas on top of the mask and the coherently grown regions over the windows. A clear reverse contrast in the cross-sectional CL images of bandedge (identical contrast in case of yellow-band) emission was observed by comparing the defect density observed in cross-sectional TEM images. The CL peak intensity ratio of band-edge-emission to yellow luminescence was also investigated as a function of position in the GaN pyramid cross section. It was demonstrated that there exists a strong correlation between structural defects and optical properties in laterally overgrown GaN pyramids on (111) Si substrate.
INTRODUCTION Wide-band-gap III nitrides have attracted much attention due to their versatile applications in optoelectronic and electronic devices. It is believed that the lateral epitaxial overgrowth (LEO) technique of the group III nitrides plays the most important role in the realization of highperformance light-emitting diodes and long lifetime cw laser diodes, since LEO is an attractive growth technique to reduce the defect density of GaN films. The LEO GaN stripes and hexagonal pyramids on patterned GaN (0001) films on sapphire, 6H-SiC (0001), and Si (111) substrates have been reported, and a dramatic reduction in dislocation density has been observed in both the GaN stripes and pyramids on sapphire, SiC (0001), and Si (111) substrates using high resolution transmission electron microscopy (TEM) [1-4]. A decrease in yellow-band emission intensity and/or an increase in band-edge emission intensity have been correlated with significant reduction in dislocation density in LEO GaN stripes [5,6]. However, it has been reported that there is no spatial correlation between dislocations and yellow-band emission in LEO GaN pyramids [7]. Until now, therefore, there has been no clear evidence to show a correlation between structural defect density and opti
Data Loading...
