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The Study of Si Surface Adsorption and Magnetism of Si-Doped Defect in GaN

Author: ZhangLei
Tutor: XingHuaiZhong
School: Donghua University
Course: Materials Physics and Chemistry
Keywords: the first principle Si(100) surface adsorption diluted magnetic semiconductors (DMS) GaN:Si magnetism
CLC: TN304.12
Type: Master's thesis
Year: 2012
Downloads: 8
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Abstract


Silicon is one of the most important semiconductor materials; the surface structures and epitaxial growth of Si have been attracting attention. It is significant to characterize and understand the microstructures of Au/Si interface due to its wide application in the electronic devices and surface catalytic engineering. By using first-principles calculations based on the density functional theory (DFT), the dissertation is devoted to the study of the surface structure and electronic properties of Au adsorbed on the surface of Si(100)p(2×2), and investigation of the magnetism of d0 in GaN and the effect of Si-doping on the magnetism in GaN. The main results are as follows:The differences of the Si(100) surface of the p(2×1), p(2×2) and c(4×2) reconstruction have been firstly studied. These reconstructions can be explained in terms of different arrangements of alternately buckled dimers. Distinguishing between p (2×1) asymmetric buckled dimers and alternately buckled dimers requires going down another order of magnitude on the energy scale. The smallest energy difference between the p(2×2) and the c(4×2) reconstructions is only 4meV. In this paper, we study the adsorption on the Si(100) p(2×2) surface, and analyse the surface charge density. The Si atoms on the Si(100) p(2×2) surface in the buckled dimer differ chemically. Because of the charge transfer from the down dimer atom(Si-down) to the up dimer atom(Si-up). Si-up is negatively charged, and Si-down is electron deficient.Then we calculated adsorption configurations of single Au atom on Si(100) p(2×2). The results indicate a global minimum energy when the Au atom is absorbed between two Si-dimer rows(BDR). The Au atom is covalently bonded to two Si atoms, and it can saturate dangling bonds of Si atoms. The covalent bond is consisted of partial ionic bonds between the Au and the surface Si atom. we investigate the adsorption of Au3 cluster on the Si(100) p(2×2), when the Au3 cluster also is adsorbed between two Si-dimer rows(BDR), the energy is smaller. After relaxtion, in the Au trimer, one Au-Au bond is broken due to the attraction of the surface Si, and the lengths of other two Au-Au bonds are decreased. Finally we study the adsorption of CdS on the Au/Si(100) p(2×2). After the full structure relaxation, the S atom is much easier adsorbed than the Cd atom on the Au/Si(100)p(2x2).Finally, using the first principle method within the local spin approximation, The magnetism of d0 in GaN and the effect of Si-doping on the magnetism in GaN are investigated. It is found that defect induced intrinsic magnetic moment of GaN is 3μB, while the magnetic moment is quenched to 2μB in Si doping GaN:Si. The moment decreases with increasing of the concentration of Si. The result is very helpful for experiment.

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