Influence of Growth Parameters on the Deep Level Spectrum in MBE-Grown n-GaN
- PDF / 108,011 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 52 Downloads / 173 Views
Y9.8.1
Influence of Growth Parameters on the Deep Level Spectrum in MBE-Grown n-GaN A. R. Arehart,1 C. Poblenz,2 B. Heying,2* J. S. Speck,2 U. K. Mishra,2 S. P. DenBaars,2 and S. A. Ringel1 1 Department of Electrical Engineering, The Ohio State University, Columbus, OH 43210 2 Materials and Electrical and Computer Engineering Departments, University of California, Santa Barbara, CA 93016 *Current Address: Northrup-Grumman, Redondo Beach, CA
ABSTRACT The impact of growth temperature and Ga/N flux ratio on deep levels in GaN grown by molecular beam epitaxy (MBE) is systematically investigated using both deep level optical spectroscopy (DLOS) and deep level transient spectroscopy (DLTS) in a study designed to map out the presence and concentration of defects over a defined region of the MBE GaN growth phase diagram. A series of Si-doped GaN films were grown to cover a substrate temperature range and a Ga/N flux ratio range that spans from the N stable to the Ga droplet regimes along both variables. Identical growth templates were used to eliminate variations in dislocations between samples so that point defect variations could be tracked. For these samples, traps are detected at EC-Et=0.25, 0.60, 0.90, 1.35, 2.40, 3.04, and 3.28 eV. The near valence bands states at EC–3.04 and EC–3.28 eV are found to be strongly dependent on Ga/N flux with decreased concentrations as a function of increasing Ga flux toward the Ga droplet regime, but with little effect from growth temperature. The EC-1.35 eV level shows a strong dependence on growth temperature and only slight dependence on Ga/N flux ratio. In contrast, the concentration of the EC-Et=0.25, 0.90 eV levels increased with increasing Ga flux toward the Ga droplet regime, while the EC-Et=0.60 shows no dependence. The variation in concentration of the EC-2.40 eV level that has been related to VGa was difficult to quantify, but tends to increase towards nitrogen rich growth. The dependencies for the detected states with respect to growth temperature and Ga/N flux ratio suggest different physical point defect sources. INTRODUCTION The importance and effect of MBE growth conditions on trap concentrations in GaN is an undetermined issue. Understanding the basic electronic properties of traps and their sources is of great interest for the GaN community and will continue to be valuable for the future understanding of material properties. Many groups have used DLTS along with irradiation, intentional impurity incorporation, and other techniques to identify the physical source of traps [1,2]. Although DLTS is a powerful technique, it only gives a limited picture of the trap spectra in GaN because it relies on detecting thermal carrier emission from traps, and experimentally only traps within about 1 eV of a band edge can be detected leaving, for GaN, more than onethird of the bandgap, centered at mid-gap, unprobed. We have used DLTS along with DLOS to probe the entire bandgap. The focus of this study is the effect of MBE growth temperature and Ga/N flux ratio on trap concentrations
Data Loading...
