Modeling of Chlorine Related Defects and Complexes in ZnMgSe
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Modeling of Chlorine Related Defects and Complexes in ZnMgSe Yaxiang Yang, Leonid Muratov, Bernard R. Cooper, and Thomas H. Myers Department of Physics, West Virginia University Morgantown, WV 26506, U. S. A. John M. Wills Theory Division, Los Alamos National Laboratory, Los Alamos, NM 87545 ABSTRACT We have used the ab-initio full potential LMTO method to model native defects and chlorine-impurity-related defects in ZnSe and ZnxMg1-xSe. Our results show that there is a strong tendency for formation of a defect complex between a chlorine impurity at the Se site and a vacancy at the neighboring Zn site. The formation energies of this complex and other chlorine related defects decrease in the presence of magnesium. However, the maximum achievable electron concentration in the presence of magnesium is lower because of the increase in the band gap. INTRODUCTION The wide-band-gap semiconductors ZnSe and its alloy ZnxMg1-xSe are of great interest because of their application to blue-green light emitting diodes and laser devices. Several calculations1-9 have been developed on the role of defects and defects complexes in ZnSe with ntype and p-type doping. Compared to ZnSe, ZnxMg1-xSe has a higher band gap, which may give an improved optical and electrical confinement. By increasing the Mg content, the band gap of ZnxMg1-xSe can be modified from 2.7eV for pure ZnSe to approximately 3.7eV for MgSe. Chlorine is the most successful n-type dopant to ZnSe, it is certainly considered as a candidate for n-type doping in ZnMgSe. Therefore, we modeled chlorine-related defects in ZnSe and ZnxMg1-xSe alloy, and focused on the changes in the electronic properties with increase of Mg content. COMPUTATIONAL APPROACH FP-LMTO Method For this calculation, we used an ab-initio full-potential linear muffin-tin-orbital method(FPLMTO) including a force routine10 with the electron exchange-correlation treated in the localdensity approximation (LDA). Detailed information about this method can be found in reference 13. Zinc 3d-electrons were treated as valence electrons, while Se 3d-electrons were included in the core. For the charged defects, a neutralizing uniform background charge was used to avoid long-range Coulomb interactions. Different concentrations of Mg were achieved by substituting one, two, or three Zn atoms with Mg atoms in a 32-atom supercell. Therefore, three ZnMgSe AA4.26.1
alloys: Zn0.94Mg0.06Se, Zn0.87Mg0.13Se, Zn0.81Mg0.19Se were considered. Lattice relaxation around the defects has been shown to be significant for ZnSe in previous works3,7,8,13. It is even more important for the present calculation since the differences on the formation energies of the same defect in ZnxMg1-xSe with different Mg content is very small. In our calculation, lattice relaxation around defects was calculated using Hellman-Feynman11 forces. In order to minimize numerical discrepancy, all calculations for a material have been performed using supercells with identical symmetry and the same k-points in the Brillouin zone. In this approach, most of the
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