Search for the Major Chlorine-Related Defects in CdTe:Cl
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Search for the Major Chlorine-Related Defects in CdTe:Cl Dmitry Krasikov1, Andrey Knizhnik1, Boris Potapkin1, Timothy Sommerer2 1 Kintech Lab Ltd., 1, Kurchatov Sq., Moscow 123182, Russia 2 GE Global Research, Niskayuna, NY 12309 U.S.A. ABSTRACT Understanding the effect of chlorine-related defects on the CdTe electric properties is important both for obtaining high resistivity CdTe-based detectors and for high efficiency CdTebased thin-film solar cells. The actual mechanism of the effect of Cl on electric properties of CdTe is not clear and different sometimes contradictory hypotheses appear. For example ClTeVCd shallow acceptor complex defect was proposed both as a reason of increased carrier concentration in CdTe thin film and also as a reason of high resistivity of CdTe:Cl thin films. In the present work we are trying to clarify the effect of Cl on CdTe electric properties and to find the reason of high resistivity of CdTe:Cl crystals using first principles calculations and defect chemistry modeling. For the first time we are trying to develop a model capable to describe experimental data on both high temperature and room temperature conductivity of CdTe:Cl. INTRODUCTION To better understand the effect of chlorine on the defect structure of CdTe it can be useful to analyze the known data on CdTe:Cl single crystals aimed for usage as radiation detectors. It has been experimentally established that the room temperature resistivity of Cl-doped CdTe single crystals increases with Cl concentration, reaching values up to 109-1010 Ω·cm [1,2,3,4]. As follows from experimental and theoretical works [5,6,7], high resistivity (HR) in CdTe cannot be obtained without deep defect levels in the band gap of CdTe. The known Cl-related defects in CdTe are shallow donors ClTe (chlorine on tellurium site) and Cli and shallow acceptor A-center [8]. Cl-related DX-centers that could provide a deep charge transition levels in the band gap are unable to be formed in CdTe crystals [9]. So, no deep Cl-related defect that can explain high resistivity of CdTe:Cl was proposed yet. As a consequence, from time to time appear the efforts to model electric properties of CdTe:Cl with shallow defects only. For example in work [8] the defect chemistry model for Cl-doped CdTe crystal was proposed that includes only shallow Cl-related defects. Authors of work [10] tried to show using defect chemistry modeling that shallow defects rather than deep defects can be responsible for CdTe:Cl high resistivity at room temperature. In the present paper we investigate the reasons of low resistivity in a system with shallow levels only, using first principles calculations and defect chemistry modeling we show that among two deep defects, Cli and ClTe-ClCd, the latter is more probably the reason of high resistivity in CdTe:Cl. CALCULATION DETAILS Optimization of the atomic structures of defects in different charge states, calculations of the formation energies and analysis of the atomistic mechanisms of the defects formation were performed using the projector augm
