Size-dependence of the Linear and Nonlinear Optical Properties of GaN Nanoclusters
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Size-dependence of the Linear and Nonlinear Optical Properties of GaN Nanoclusters
Andrew C. Pineda1,2 and Shashi P. Karna3 US Air Force Research Laboratory, Space Vehicles Directorate, 3550 Aberdeen Ave, SE, Bldg. 914, Kirtland Air Force Base, New Mexico 87117-5776 2 The Center for High Performance Computing and Department of Chemistry, The University of New Mexico, MSC01 1190, 1 University of New Mexico, Albuquerque, NM 87131-0001 3 US Army Research Laboratory, Weapons and Materials Directorate, ATTN: AMSRD-ARLWMBD, Bldg. 4600, Aberdeen Proving Ground, MD 21005-5069 1
ABSTRACT
In this paper, we present the results of our first-principles quantum mechanical studies of the electronic structure, geometry, and linear and nonlinear optical (NLO) properties of tetrahedral GamNm (m=1, 4, 7, 17) atomic clusters. Our calculated results suggest that the linear and NLO properties both exhibit a strong dependence upon cluster size and shape (geometry). However, the size- and the geometry-dependences are more pronounced for the NLO properties than for the linear optical properties. For clusters containing equal numbers of Ga and N atoms, an open-structure with no network-forming ring has a much larger second-order NLO coefficient than a cluster with a closed ring structure.
INTRODUCTION
The linear and nonlinear optical properties of III-V binary semiconductors have been the subject of active research since the late 1960s [1,2]. Recent advancements in (a) experimental techniques to fabricate/produce stable isolated nanometer-size binary atomic clusters composed of group III and group V elements and (b) techniques and tools to probe response properties of nanoscale objects, have attracted a great deal of attention to the linear and nonlinear optical properties of III-V nanoclusters due to their potential applications in future communications technologies [3]. An important issue in a bottom-up approach to fabricating nanoclusters for future technological applications is an understanding of the evolution of their response properties with cluster size and shape. Theoretical work on atomic clusters of III-V semiconductors have examined the electronic structure and stability of small clusters using density functional theory [4,5] and their linear and non-linear optical properties using the ab initio time dependent HartreeFock formalism [6,7,8] as well as time-dependent density functional theory [9]. Work by Kandalam et al. suggests that as cluster sizes increase a transition from low energy planar to
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bulk-like 3-D structures occurs in some nitrides [4]. As non-linear optical properties of molecules are particularly sensitive to their 3-D structure, this suggests a strong dependence of the NLO properties on cluster size. Indeed, work by Natarajan et al. on the atomic and electronic structures of IV-VI semiconductor structures (GemTen, m+n ≤ 10) suggest that the polarizabilities of the clusters vary non-monotonically with cluster size [10]. In order to better understand the dependence of optical properties on g
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