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The Doping Property of Alpha-quartz Crystal: A First-principles Calculation

Author: HanDong
Tutor: SunHongBo
School: Jilin University
Course: Microelectronics and Solid State Electronics
Keywords: Quartz crystal doping first-principles DFT parallel computing
CLC: O474
Type: Master's thesis
Year: 2009
Downloads: 107
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Abstract


Quartz material is on of the most common mineral. It is of stable properties in both physics and chemistry. Quartz material which effects our daily lives is used widely. In Stone Age, people have begun to make stone axes and stone arrows with quartz. They use the simple production tools to hunt for food and fight against the enemy.The quartz material has been researched extensively with the development of modern science and technology. People made a variety of devices based on its optical and electrical properties. The research on quartz properties and application of quartz material are changing our life tremendously and promoting the social progress greatly. Therefore,exploring the new application field of quartz material is very important.With the rapid development of microelectronics industry, the semiconductor materials require a wide bandgap, high fire-resistant, high mobility. Research on semiconductor’s properties, especially doping property on wide bandgap semiconductor materials is of great significance. Therefore, quartz crystal doping property analysis is very important and Research on quartz doping property helps us to research the doping property of other wide bandgap materials.The main work in this paper is to explore the doping characteristics of silicon dioxide in atomic and electronic scale. The method is first-principles calculation based on Density Functional Theory (DFT).Characterizing the property of materials using first principle based on DFT, calculating the multi-electron system composed of hundreds of atoms, solving the Schr?dinger equation exactly, and computing the system total energy, are not an easy task. Considering the complexity and accuracy of system computing, Not only the calculation time is not tolerable, but also storage is not provided for computing data, if we use personal computer (PC) as the computing environment. However, the supercomputer can provide both abundant storage and little computing time consumption, but computing cost is so high that we can’t offer it. Supercomputer is not suitable in our research. Therefore, considering our research, building a suitable parallel computing environment is problem we must solve firstly. After analyzing the components of parallel computing system, in the tolerable computing time consumption, we confirm Cluster which is composed of PC, gigabit Ethernet, TCP/IP and MPI as our parallel computing environment. This combination is low cost, efficient, mature and easy to assemble. We have tested the eight-node parallel computing environment based on Intel Q6600 processor. The highest linpack mark of this parallel computing environment is 185.1Gflops. The efficiency of eight-node parallel computing is 74%. It is a good parallel efficiency. The parallel computing environment has an effective parallel computing acceleration in practical tasks and meets the requirement of the theoretical calculation.The core work in this paper is to explore the doping characteristics of alpha-quartz crystal using first principle based on DFT. These impurities doping in alpha-quartz crystal include theⅢA elements (P-type),ⅤA elements (N-type) substituting silicon atom andⅤA elements (P-type) substituting oxygen atom.After calculation, we find the bond length change differently. The bond length between the impurity ofⅢA elements (B, Al, Ga) substituting silicon atom and the four neighboring oxygen atoms doesn’t change significantly with the charge change of the doping supercell. The electron around the impurity is delocalized. The bond length between the impurity thatⅤA elements (N, P, As) substituting silicon atom and the four neighboring oxygen atoms gets longer with the charge of the doping supercell is increasing. The electron around the impurity is localized. The bond length between the impurity thatⅤA elements (N, P, As) substituting oxygen atom and the neighboring silicon atoms get shorter with the charge of the doping supercell is increasing. We explain the bond length change differently with the change of Coulomb interaction among atoms and the redistribution of electron density.We also calculate the formation energy of impurities in alpha-quartz in this paper. The substituting impurities in alpha-quartz have a relative high formation energy according to the formation energy formula. This is due to the larger distance between crystal atoms, impurity atoms tend to be interstitial site rather than the lattice. We calculate the defect levels in bandgap using the impurity formation energy. The result show that quartz has a tendency of asymmetric doping characteristic, i.e. shallow acceptor and deep donor. The defect levels E(-1/0) ofⅢA elements (B, Al, Ga) substituting silicon atom is 0.47eV, 0.34eV and 0.27eV above the valence band maximum (VBM), respectively. The defect levels E(+1/0) ofⅤA elements (N, P, As) substituting silicon atom is 4.00eV, 6.08eV and 3.60eV above the VBM, respectively. The defect levels E(-1/0) ofⅤA elements (N, P, As) substituting oxygen atom is 1.59eV, 3.17eV and 3.45eV above the VBM, respectively. The alpha-quartz crystal has a doping polarity as other wide bandgap materials have.

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CLC: > Mathematical sciences and chemical > Physics > Semiconductor physics > Impurities and defects
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