Properties of InGaN/GaN Quantum Wells Grown by Metalorganic Chemical Vapor Deposition
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Properties of InGaN/GaN Quantum Wells Grown by Metalorganic Chemical Vapor Deposition M. G. Cheong, K. S. Kim, C. S. Kim, R. J. Choi, H. S. Yoon, S. W. Yu, Y. K. Hong, C.-H. Hong, E.-K. Suh, and H. J. Lee Semiconductor Physics Research Center (SPRC) Chonbuk National University, Chonju 561-756, KOREA ABSTRACT Optical and structural properties of InGaN/GaN quantum wells having growth interruption were investigated using high-resolution x-ray diffraction, photoluminescence and transmission microscopy. InxGa1-xN/GaN (x>0.25) six pair quantum wells used in this study were grown on cplane sapphire by metalorganic chemical vapor deposition. The growth interruption was carried out by closing the group-III metal organic sources before and after growth of InGaN quantum well layers. With increasing the interruption time, the quantum dot-like region and well thickness decreases due to indium re-evaporation or thermal etching effect. As a result, PL peak position is blue-shifted and intensity is reduced. The size and number of V-defect did not vary with interruption time. The interruption time is not directly related with formation of the defect. The V-defect in quantum wells originates at threading dislocations and inversion domain boundaries due to higher misfit strain. . INTRODUCTION Blue and green light emitting diodes (LEDs) and laser diodes (LDs) have been amazingly progressed by using InGaN/GaN quantum wells (QWs) as active materials [1,2]. However, despite the remarkable progress in device performance, comprehension of InGaN/GaN QW is still an active research field. Recently, the compositional fluctuation of In and V-defects in InGaN/GaN have been studied about their roles and origins [3-7]. It is generally believed that the V-defect originates at a threading dislocation (TD) due to the high lattice mismatch between GaN and the substrate [8]. It has been reported that strain relaxation occurs via surface roughening, which lead to the three-dimensional growth in the top of the structure forming facets with a Vshape on the {10-11} planes [9]. In this work, we investigate the effect of interruption time on optical and structural properties of InxGa1-xN/GaN (x>0.25) six pairs QWs (6QWs). Especially we have studied about the QD-like localized state and V-defect using photoluminescence (PL), transmission electron microscopy (TEM), and high resolution X-ray diffraction (HRXRD).
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EXPERIMENTS All samples were grown on c-plane sapphire substrates. After loaded into the reactor, the substrates were thermally cleaned in hydrogen ambient for 10 minutes at 1100 oC, and then 25 nm thick GaN nucleation layer was grown at 560 oC. The InGaN/GaN QWs with interruption time of 0, 10, 30, 60 second were deposited after growing 2 µm thick Si-doped GaN layer on the nucleation layer at 1130 oC. The growth interruption was carried out by only closing the group-III metal organic sources before and after the growth of InGaN well layers. To compare the surface of the InGaN/GaN QWs, optical measurements and atomic force microscopy (AFM) we
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