Structural and Optical Properties of InGaN/GaN Multi-Quantum Well Structures with Different Well Widths
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Structural and Optical Properties of InGaN/GaN Multi-Quantum Well Structures with Different Well Widths
Young-Hoon KIM 2, Chang-Soo KIM, Sam-Kyu NOH, Jae-Young LEEM, Kee-Young LIM 1, Byung-Sung O 2 and Jay P. SONG 3 National Research Laboratory on Quantum Dot Technology, Materials Evaluation Center, Korea Research Institute of Standards and Science, Taejon, Korea 305-600 1 Semiconductor Physics Research center and Department of Semiconductor Science and Technology, Chonbuk National University, Chonju, Korea 561-756 2 Department of Physics, Chungnam National University, Taejon, korea 305-764 3 SongJee Industrial Corporation, Sungnam, Korea 463-500
ABSTRACT The structural and the optical properties of 10-period In0.15Ga0.85N/GaN multiple quantum wells (MQWs) have been investigated using HRXRD (high-resolution X-ray diffraction) and PL (photoluminescence). For the samples, the barrier thickness was kept constant, 7.5 nm and the well thicknesses were varied, 1.5, 3.0, 4.5, and 6.0 nm. For the structural characterization, an ω/2θ-scan and an ω-scan for GaN (00·2) reflection and a reciprocal space mapping (RSM) around the GaN (10·5) lattice point were employed. The average strain for the MQWs increased as the well thickness increased. The MQW with a 6.0 nm well thickness experienced lattice relaxation and the crystallinity of the sample was poor compared to that of the other samples. MQWs with well thicknesses of 1.5, 3.0 and 4.5 nm, however, maintained lattice coherency with the GaN epilayers underneath, and the critical well thickness for lattice relaxation of the MQWs used in the study was 6.0 nm. The PL spectra showed that the relative emission intensity of the sample with a 6.0 nm well thickness was lower than for the others, a fact consistent with the X-ray results. The emission intensity, therefore, is considered to be affected by defects due to lattice relaxation of the epilayer.
INTRODUCTION The III-V nitrides such as GaN, InN and AlN are candidate materials for light-emitting diodes (LEDs), laser diodes (LDs) and high power transistors due to their wide band gaps, K7.12.1 Downloaded from https:/www.cambridge.org/core. Columbia University Libraries, on 11 Jul 2017 at 03:09:43, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-722-K7.12
thermal stability and strong bond strength [1]. InGaN/GaN multiple quantum wells (MQWs) have been used as active layers for blue LDs. For InGaN/GaN quantum well structures, two different radiative recombination mechanisms are generally accepted [2]. For a GaN epilayer, heteroepitaxial growth on a sapphire substrate has commonly been employed. It has been very difficult to grow a high quality GaN film with a smooth surface because of the large lattice and thermal mismatches between GaN and sapphire. The InGaN layer grown on GaN experiences a compressive biaxial strain. As the thickness of the strained layer exceeds a critical value, the accumulated elastic energy is relieved by the formation of misfit disl
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