Characterization of Nano-size Indium Cluster in InGaN/GaN Multiple QuantumWells with High Indium Composition
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Characterization of Nano-size Indium Cluster in InGaN/GaN Multiple Quantum Wells with High Indium Composition Hyung Koun Cho and Jeong Yong Lee1 Department of Metallurgical Engineering, Dong-A University, Hadan-2-Dong 840, Saha-gu, Busan, 604-714, KOREA; 1 Department of Material Science and Engineering, KAIST, Daejeon 305-701, Korea
ABSTRACT We report the effect of strain-induced indium clustering on the emission properties of InGaN/GaN multiple quantum wells grown with high indium composition by MOCVD. Nanosize indium clustering confirmed by high-resolution transmission electron microscopy results in the redshift of the emission peak and the increase of the integrated photoluminescence (PL) intensity. We found that strong carrier localization in indium clustering induces the increases of the activation energy of PL integrated intensity and the temperature independence of PL decay profiles. All these observations suggest structurally and optically that the improved emission properties in the InGaN/GaN multiple quantum well with high indium composition are associated with the localized states in the nano-size indium cluster. INTRODUCTION The manufacture of high-brightness light emitting diodes (LEDs) with various colors can be obtained by growing InxGa1−xN as the active layer [1]. In principle, the band gap of InxGa1−xN can be varied over nearly the whole spectral range from near ultra violet (UV) emission (the 3.44 eV of GaN) to red emission (the 1.9 eV of InN). It has been proposed that despite their excessive structural defects such as dislocations, stacking faults, inversion domain boundaries, etc. strong emission from InGaN/GaN multiple quantum wells (MQWs) was caused by the recombination of excitons localized in indium-rich regions, which act as self assembled quantum dots [2]. To achieve longer wavelength LEDs, higher indium composition in InxGa1−xN/GaN MQW structures as an active material is required. An increase in indium composition results in the large lattice mismatch between InGaN wells and GaN barriers. In this study, we report the effect of indium clustering on characteristics of InGaN/GaN MQW with high indium composition using samples with and without indium clustering obtained by growth interruption between InGaN and GaN.
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EXPERIMENTAL DETAILS All samples were grown on c-plane sapphire substrates with a nominal 25 nm thick GaN buffer layer by a horizontal metal-organic chemical vapor deposition reactor operating at low pressure. The indium compositions of the InxGa1−xN well layers of the MQWs grown without interruption (sample I0) and with 10 s interruption (sample I10) between the InGaN well and GaN barrier are expected to be 31 and 28 %, respectively. Also, the thicknesses of the wells and barriers are 15 Å and 85 Å, respectively. For photolum
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