First Principles Study on the Effects of Vacancies and Mg Doping on the Physical Properties of CuAlO2, AgAlO2, CuCrO2, and AgCrO2 Transparent Conductor Oxides
Date
2018-08
Authors
Shook, James A.
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Abstract
The need for well understood, commercially available p-type transparent conducting oxides for incorporation into basic transparent semiconducting devices alongside their already well understood and available n-type counterparts for application in technologies such as solar cells and capacitive touchscreens motivates this first principles study on the effects of Cu and O vacancies and Mg doping on the intrinsically poor p-type character of CuAlO2, AgAlO2, CuCrO2, and AgCrO2. Density functional theory based calculations using the projector augmented-wave functions along with the generalized gradient approximation to the exchange and correlation energy as implemented by the Vienna Ab Initio Simulation Package are used to study the total crystal energy of the three known polymorphs of CuAlO2 and AgAlO2 in order to determine the most stable polymorph in the ground state. Additionally, three simple magnetic configurations are considered for CuCrO2 and AgCrO2 in the context of total energy of the ground state for the purpose of choosing a specific polymorph and magnetic configuration to be the framework within which the doped and defect systems will be studied. Different functional approaches to the exchange and correlation energies are also considered in order to accurately reproduce the structural properties and the band gap. The 2H delafossite polymorph is determined to be one of the most stable polymorphs and is the focus of this work as it is the least studied of the delafossites. The simple antiferromagnetic configuration is chosen to model magnetic effects in CuCrO2 and AgCrO2 due to it having one of the lowest ground state total energies and also containing the most semiconductor like behavior of the magnetic configurations considered. A 2x2x2 supercell scheme is employed to model 6.25% Cu and Ag vacancies, 3.13% O vacancies, and 6.25% Mg-doping replacing Al and Cr, from which structural properties, electronic properties, hole effective masses, and optical properties are obtained and compared to the pristine crystal in order to offer predictions on the effectiveness of the mentioned native defects and dopant on increasing the conductivity and maintaining transparency in all transparent conducting oxides studied in this work. Comparisons between the results obtained in this work and previous experimental and other theoretical results are made, when available. Many of the properties predicted here are immediately testable via experimentation.
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Keywords
Transparent conducting oxides, Physics, Density Functional Theory, Crystal structure, Electronic structure, Hole effective masses, Optical properties, Defects, Dopants
Citation
Shook, J. A. (2018). <i>First principles study on the effects of vacancies and Mg doping on the physical properties of CuAlO2, AgAlO2, CuCrO2, and AgCrO2 transparent conductor oxides</i> (Unpublished thesis). Texas State University, San Marcos, Texas.