Michigan Technological University
Department of Physics

is pleased to announce a colloquium

with

Miguel Blanco

Simulation of Point Defects using Cluster-in-the-Lattice Techniques: Applications to Chalcopyrite Semiconductors

Cluster-in-the-lattice techniques have been used as early as 1963 to investigate the structural and electronic properties of point defects. They consist of a cluster model of the defect and its near environment, solved by conventional molecular quantum mechanics methods, plus a model to accommodate this cluster to its actual long-range environment in a perfect crystal, the so-called embedding technique. In this long-term collaboration between MTU and the University of Oviedo, we have developed a new embedding scheme, whose main advantage is that it allows the use of standard state-of-the-art programs (e.g. Gaussian98) to perform high-quality calculations of the electronic structure and relaxation effects of the defects. This scheme involves several levels of decreasing detail for the description of the embedding at increasing distances from the point defect. The quality of the embedding model is tested using the self-embedding procedure: a cluster model for the perfect crystal centers is created as if they were point defects, and then compared with a periodic perfect crystal calculation. All of the above techniques are currently being used to simulate point defects in semiconductors with non-linear optical properties, namely the chalcopyrites ZnGeP₂ and CdGeAs₂. Several important defects are under investigation: Zn vacancies and O, S, Se substitutionals (P-site) in ZnGeP₂ and the Ge antisite (substituting As) in CdGeAs₂. The local geometry of these defects, its formation energies, and the spin density and ionization potential for an electron trapped in them are being calculated and compared with the results of EPR measurements.

Thursday, December 5, 2002

4:00 p.m., Fisher 139

Refreshments will be served

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