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NERSC Initiative for Scientific Exploration (NISE) 2011 Awards

Deep Defect States and Valence Skipping in Narrow Band Gap Semiconductors

Mal Soon Lee, Michigan State University

Associated NERSC Project: Revolutionary Materials for Solid State Energy Conversion (m968), Principal Investigator: S. D. Mahanti

NISE Award: 340,000 Hours
Award Date: March 2011

This project will help us to understand why a particular structure is energetically stable for a given system and why in some structures two different types of local geometry and/or different valence states appear in narrow band gap semiconductors. In addition, it will help us to understand how defect states depend on this mixed valency.

The origin of valence skipping in low dimensional semiconductors and the role of mixed valency on the nature of deep defect states in narrow band gap semiconductors (of thermoelectric and photovoltaic interest) are of great current experimental and theoretical interest. In this proposal we address two fundamental questions in these systems. They are (1) the relationship between competing local bonding, local geometry, mixed valency (skipping valency), and the global structure (quasi 1-dimension and/or 2-dimension) in a class of important binary chalcogenides MX, where M=Ga, In, Tl; X=e, Te, and (2) the nature of deep defect states in these binary systems.