Journal of Crystal Growth 242 (2002) 35–40 Effects of post-growth thermal annealing on the indium aggregated structures in InGaN/GaN quantum wells Yen-Sheng Lin a , Kung-Jen Ma a , C.C. Yang b, *, Thomas E. Weirich c a Department of Mechanical Engineering, Chung Cheng Institute of Technology, National Defense University, Tahsi, Taoyuan, Taiwan, ROC b Department of Electrical Engineering, Graduate Institute of Electro-Optical Engineering and Graduate Institute of Electronics Engineering, National Taiwan University, 1, Roosevelt Road, Sec. 4, Taipei, Taiwan, ROC c The Center of Electron Microscopy, Aachen University of Technology, Ahornstr. 55, D-52074 Aachen, Germany Received 6 February 2002; accepted 4 April 2002 Communicated by T. Nishinaga Abstract Size and distribution of indium-rich quantum dots (QDs) are important parameters for improving photon emission efficiency of InGaN/GaN quantum well (QW) structures. Our results showed that post-growth thermal annealing of such a sample with temperature ranging from 8001C to 9001C led to a better confinement of indium-rich clusters near InGaN QW layers. Transmission electron microcopy (TEM) and energy filter TEM results manifested that the sizes of indium-rich QDs were reduced with increasing annealing temperature. Also, the size homogeneity was improved. Quasi-regular arrays of indium-rich QDs embedded in InGaN QWs were observed in the sample of 9001C annealing. X-ray diffraction also showed the enhancement of InN relative intensity. Photoluminescence measurements revealed blue shifts of photon emission spectral peak, indicating stronger quantum confinement after thermal annealing. However, such a process of regular QD formation disappeared when annealing temperature was increased to 9501C. In this situation, coarsening of indium-rich clusters occurred and their distribution became irregular. r 2002 Elsevier Science B.V. All rights reserved. Keywords: A1. Segregation; A3. Quantum wells; B1. Nitrides; B2. Semiconducting III–V materials 1. Introduction Indium-rich clusters near InGaN quantum well (QW) layers in an InGaN/GaN QW structure are closely related to the photon emission efficiency of such a compound [1,2]. The localized energy states formed at these clusters can trap carriers for photon emission and reduce non-radiative recom- bination rate. This trapping process is particularly important in such a normally high defect density material. In order to achieve optimum perfor- mance of a practical device, regular structures of indium-rich clusters are preferred, including their sizes, shapes and distributions [3,4]. Regular structures result in purer spectra and hence higher quantum efficiencies at preferred photon energies. *Corresponding author. Tel.: +886-2-2365-7624; fax: +886- 2-2365-2637. E-mail address: ccy@cc.ee.ntu.edu.tw (C.C. Yang). 0022-0248/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII:S0022-0248(02)01328-3