Optimization of GaN Barriers During the Growth of InGaN/GaN Quantum Wells at Low Temperature
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1108-A04-06
Optimization of GaN barriers during the growth of InGaN / GaN quantum wells at low temperature
Kalyan R Kasarla1, 2, W. Chiang1, R. Rahimi1 and D. Korakakis1, 2. 1
Lane Department of Computer Science and Electrical Engineering, West Virginia
University, P.O.Box 6109, Morgantown, WV 26506-6109, U.S.A. 2
National Energy Technology Laboratory, 3610 Collins Ferry Road, Morgantown, WV
26507 – 0880, U.S.A.
ABSTRACT InGaN/GaN MQWs are grown on c-plane sapphire substrates using a low pressure metal organic vapor phase epitaxy (MOVPE) system. Trimethylgallium (TMGa), Triethylgallium (TEGa), Trimethylindium (TMIn) and ammonia were used as precursors for Ga, In and N, respectively and the growths were carried out at low temperature. Structural properties of grown MQWs are characterized using atomic force microscopy (AFM), and scanning electron microscope (SEM) and x-ray diffraction technique (XRD) is used to calculate the Indium incorporation in these MQWs. Surface morphologies over large areas of InGaN/GaN MQWs are observed using the tapping mode AFM; results indicate the surface roughness depends on the barrier thickness. Density of V- defects, effect of barrier width on the surface morphology and also on Vdefect density will be presented and discussed.
INTRODUCTION Group III- nitrides have emerged as a promising material system for optoelectronic applications ranging from infrared to ultraviolet regions as well as for high power/high temperature and high frequency electronics. In particular, quantum wells (QWs) based on InGaN active layers have been playing a key role in the achievement of high brightness blue and green light emitting diodes (LEDs) and laser diodes (LDs) [1,2]. Inspite of the progress made during last several years in the growth technologies; there are still a lot of unresolved issues related to InGaN multi quantum well (MQW) growth. Large lattice mismatch and low miscibility between InN and GaN lead to misfit dislocations and stacking faults, also In incorporation decreases with increase in growth
temperature. The lower growth temperature of barriers in these MQW’s is followed by an increase in V-defects which affect the reliability and the lifetime of the devices. It has been shown that the growth of these barriers at an increased temperature when compared to the growth of the InGaN well will reduce the density of these defects [3]. In this work the effect of barrier width on the defect density and surface morphology of the InGaN / GaN MQWs is reported. EXPERIMENTAL DETAILS All the samples are grown on c – plane sapphire substrates using an AIXTRON 200/4 RF – S horizontal metal organic vapor phase Epitaxy (MOVPE) reactor. A thin layer of AlN (~30nm) is used as the buffer layer before the growth of 1.5µm thick n type GaN at higher growth temperature. Trimethylaluminum is used as the precursor during the growth of AlN and Trimethylgallium is used as the precursor for GaN, H2 is used as the carrier gas and NH3 as a source for nitrogen during the growth of the above two layers. This was
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