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Role of threading dislocations on Indium distribution in InGaN alloys

Huaping Lei 1,3Pierre Ruterana 1Jun Chen 2Xunya Jiang 3

1. CIMAP, CNRS-ENSICAEN-CEA-UCBN, 6 Boulevard Maréchal Juin, Caen 14050, France
2. Laboratoire de Recherche sur les Propriétés des Matériaux Nouveaux, Université de Caen, Damigny 61250, France
3. Shanghai Institute of Microsystem and Information Technology, CAS, Changning Road 865, Shanghai 200050, China

Despite the presence of high density threading dislocations, InGaN alloys and quantum wells still exhibit high efficiency light emission, and this has been subject of research interest from the scientific and industry fields for the last few years. This peculiar behavior has been related to the properties of the threading dislocations and the localization of excitons. One of the explanations to the exciton localization has been the possible formation of In-rich clusters. Theoretical investigations have pointed out that a miscibility gap exists in the InGaN ternary alloys grown under equilibrium conditions. Therefore, if the growth temperature is below a critical temperature, InGaN alloys are due to be unstable over most of the composition range and In-rich and Ga-rich regions may form in the quantum well areas. However, number experimental reports have shown that down to the nanometric scale, In-rich clusters may not exist in InGaN high quality QWs. In fact, it appears that In clustering can be suppressed by strain in InGaN/GaN heterostructures as reported in recent experimental and theoretical investigations.  However, phase separation has been found to nucleate with the aid of the threading dislocations having screw component in InGaN films [1], whereas the nucleation of InN quantum dots grown by MBE [2] and MOCVD [3] are associated with threading dislocations with edge component from the GaN buffer layer. In this work, as the In-rich clusters and threading dislocations involve hundreds to thousands of atoms, the empirical Stillinger-Weber potential is used to investigate the energetic stability of In-rich clusters in InGaN QWs and the role of the screw dislocations on the phase separation. The results indicate that In-rich clusters are not energetically favorable; however, indium atoms are found to be able to aggregate towards the dislocation core and to form In-rich regions by the screw dislocation with a full core configuration. This is explained based on the relaxation of the dislocation core in GaN by indium atoms.



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Presentation: Poster at E-MRS Fall Meeting 2009, Symposium A, by Huaping Lei
See On-line Journal of E-MRS Fall Meeting 2009

Submitted: 2009-05-22 18:02
Revised:   2009-06-07 00:48