Electron Beam Bombardment Induced Decrease of Cathodoluminescence Intensity from GaN Not Caused by Absorption in Buildup
- PDF / 173,833 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 79 Downloads / 208 Views
Internet Journal Nitride Semiconductor Research
Electron Beam Bombardment Induced Decrease of Cathodoluminescence Intensity from GaN Not Caused by Absorption in Buildup of Carbon Contamination Eva M. Campo 1, G. S. Cargill III1, Milan Pophristic2 and Ian Ferguson3 1Lehigh
University, Corporation, 3Georgia Institute of Technology, 2EMCORE
(Received Thursday, July 1, 2004; accepted Tuesday, November 30, 2004)
Monochromatic CL imaging, CL spectra, WDS spectra, and EDS spectra and imaging demonstrate that electron beam bombardment of LEO-GaN causes decrease of near band edge cathodoluminescence intensity that cannot be attributed to absorption in a growing carbon contamination layer. An alternative explanation is needed, such as generation of defects, or charge injection and buildup of internal electric fields, caused by electron beam bombardment.
1 Introduction A wide variety of electron beam irradiation and degradation effects have been reported for GaN-based materials. The electron beam induced effects include increases [1] or decreases [2] in cathodoluminescence (CL) intensities and changes in the spectral distribution of CL emission. The effects have been attributed to electronbeam enhancement of impurity diffusion [2], to changes in activated dopant concentrations, to deep levels created by local heating, to increasing uniformity of doping, to creation of vacancies, to annealing out of defects [3] , and to absorption by contamination layers [2]. Fuller understanding of the mechanisms involved in electron beam irradiation may lead to better control of defects in GaN and to better control of degradation of GaN-based devices. Carbon complexes can be deposited on a surface irradiated by an electron beam in a scanning electron microscope (SEM). Two possible sources of carbon contamination on a sample in an SEM [4] are vacuum pump oil, particularly for diffusion pumped systems, and the sample itself, since cleaning samples with organic solvents can introduce carbon residues. The GaN lateral epitaxy overgrowth (LEO) samples described in this paper have been subjected to a series of electron beam irradiation treatments [4] to study effects of irradiation on luminescence. Experiments with these samples show that electron beam irradiation causes a decrease in the intensity of near band edge (NBE)
cathodoluminescence that cannot be attributed to absorption by a contamination layer. An alternative explanation is proposed based on charge injection and buildup of internal electric fields. 2
Experimental
GaN samples were grown by MOCVD in Emcore Spectrablue reactors at Emcore Inc. Samples were LEOgrown on sapphire with SiNx masks and GaN buffer layers. A 2 µm thick GaN buffer layer was first grown on a oriented sapphire substrate, followed by a 100nm thick SiNx mask layer in which patterns of windows were produced by lithographic methods. Sample #1 had a 4 µm wide mask and sample #2 had a 8 µm wide mask. The window openings in the masks were 4 µm wide for both samples. The windows in the mask were oriented along for sam
Data Loading...
