Ⅱ-Ⅵ族三元合金半导体热力学性质的第一性原理研究

发布时间：2019-05-23 18:30

【摘要】：ZnO及其它Ⅱ-Ⅵ族半导体材料由于其优异的性能而在光电、压电、热电、铁电等诸多领域被广泛应用。自上世纪90年代ZnO薄膜在室温下发生光泵浦激发近紫外激光发射的现象被报道后,ZnO作为新型的光电信息功能材料引起了研究热潮。然而要实现ZnO在光电器件上的应用,必须解决ZnO的能带工程(能隙调控)和p型掺杂两大关键问题。ZnO的能带调控一般通过等价离子的取代来实现,例如阳离子部分取代Zn形成MeZnO(Me = Mg,Be,Cd等)三元合金或阴离子取代O形成ZnOX(X = S,Se,Te等)三元合金。研究表明,等价阳离子部分取代Zn形成的MeZnO(Me = Be,Mg,Cd等)合金中会存在相分离,并且Me的固溶度有限。在理论上,目前对Ⅱ-Ⅵ族三元合金的固溶体性质进行深入研究的报道比较少。本文采用第一性原理计算结合集团展开法,研究了CdxZn1-xO、BexZn1-xO、MgxZn1-xO、CdO1-xSx和ZnS1-xSe等Ⅱ-Ⅵ族三元合金固溶体的热力学性质。分析了不同成分下 CdxZn1-xO、BexZn1-xO、MgxZn1-xO、CdO1-xSx和ZnS1-xSex等三元合金的形成能和相图,主要研究内容及结论如下:(1)计算了纤锌矿(WZ)和岩盐矿(RS)CdxZn1-xO三元合金的形成能和相图。通过形成能的计算,发现大部分CdxZn1-xO合金构型的形成能都大于零,表明ZnO和CdO在低温下难于结合形成固溶体。进一步计算发现了 WZ-CdxZn1-xO合金的两个亚稳相结构(Cd1/3Zn2/3O 和 Cd2/3Zn1/3O)。对 Cd1/3Zn2/3O 和 Cd2/3Zn1/3O 两个亚稳相的晶格常数a和c、键长、O-Zn(Cd)-O键角以及电子结构进行分析发现,随着Cd在WZ-CdxZn1-xO合金中含量的增大,晶格常数a和c都逐渐增大,然而晶格常数的比值c/a逐渐减小。同样,随着Cd掺杂量的增大,O-Zn(Cd)-O键角大小和能带带隙逐渐变小。计算分析了纤锌矿和岩盐矿结构CdxZn1-xO的有效集团交互系数,发现双原子组成的集团在有效集团交互系数中占主导,表明双原子组成的集团对形成能的贡献最大。通过计算WZ-CdxZn1-xO和RS-CdxZn1xO合金的两相相图,发现在1600 K时Cd在WZ-ZnO中的固溶度为0.13,然而Zn在RS-CdO中的固溶度为0.01。(2)计算了纤锌矿和闪锌矿结构(ZB)BexZn1-xO的形成能和热力学相图。通过形成能的计算,发现大部分BexZn1-xO合金构型的形成能都大于零,表明ZnO与BeO在低温下难于结合形成固溶体。WZ-BexZn1-xO和ZB-BexZn1-x)的有效集团交互系数计算显示,对于WZ-BexZn1-xO来说,双原子和四个原子组成的集团在有效集团交互系数中占主导作用,表明双原子和四个原子的集团对形成能的贡献最大。对于ZB-BexZn1-xO来说,双原子组成的集团在有效集团交互系数中占主导,表明双原子组成的集团对形成能的贡献最大。文章通过计算纤锌矿和闪锌矿BexZn1-xO的相图发现,声子振动对纤锌矿和闪锌矿BexZn1xO的相图影响很大。晶格振动对Be(Zn)在ZnO(BeO)中的固溶度具有很大的影响。(3)计算了纤锌矿和岩盐矿结构MgxZn1-xO合金的形成能和热力学相图。通过计算MgxZn1-xO的形成能,发现在低温下大部分MgxZn1-xO合金构型的形成能都小于零,表明ZnO与MgO在低温下容易结合形成固溶体。同样计算了纤锌矿和岩盐矿结构MgxZn1-xO的有效集团交互系数。由有效集团交互系数得出对MgxZn1-xO来说,双原子组成的集团在有效集团交互系数中占主导,表明双原子组成的集团对MgxZn1-xO形成能的贡献最大。对WZ-MgxZn1-xO和RS-MgxZn1-xO的两相相图分析发现Mg较难固溶于纤锌矿型的ZnO中,而Zn较容易固溶于岩盐矿结构的MgO中。(4)计算了纤锌矿和岩盐矿结构CdO1-xSx的形成能和热力学相图。通过计算CdO1-xSx的形成能,发现大部分CdO1-xSx合金构型的形成能都大于零,表明在低温下CdO与CdS难于结合形成固溶体。同样计算了纤锌矿和岩盐矿结构CdO1-xSx的有效集团交互系数。双原子组成的集团在有效集团交互系数中占主导,表明双原子组成的集团对CdO1-xSx形成能的贡献最大。计算和分析了 WZ-CdO1-xSx和RS-CdO1-xSx的两相相图,研究得到S较难固溶于RS-CdO中,而O较容易固溶于WZ-CdS中。(5)对WZ-ZnS1-xSex和ZB-ZnS1-xSex的形成能和相图等热力学性质进行了研究。通过计算纤锌矿和闪锌矿结构ZnS1-xSex的形成能,发现大部分ZnS1-xSex合金构型的形成能都大于零,表明ZnS与ZnSe在低温下难于结合形成固溶体。由有效集团交互系数分析发现双原子组成的集团在有效集团交互系数中占主导,表明双原子组成的集团对形成能的贡献最大。计算并且分析了 ZnS1-xSex合金的x-T相图,发现不管是纤锌矿结构还是闪锌矿结构合金,Se在ZnS中的固溶度与S在ZnSe中的固溶度基本上相等。对于上述5个体系的半导体合金,通过比较发现集团展开法计算的形成能和采用第一性原理计算的形成能两者基本相等,从而证实了采用集团展开法计算合金形成能的有效性与可行性。
[Abstract]:ZnO and other II-VI semiconductor materials are widely used in the fields of photoelectric, piezoelectric, pyroelectric, ferroelectric and the like due to its excellent performance. As the phenomenon of ZnO thin film excited near-ultraviolet laser emission at room temperature has been reported in the 1990s, ZnO as a new type of photoelectric information function material has caused a research upsurge. However, it is necessary to solve the two key problems of the energy band engineering (energy gap regulation) and p-type doping of ZnO. The energy band regulation of ZnO is generally realized by the substitution of equivalent ions, for example, the cation part is substituted for Zn to form a ternary alloy of MeZnO (Me = Mg, Be, Cd, etc.) or an anion-substituted O to form a ternary alloy of ZnOX (X = S, Se, Te, etc.). The results show that the equivalent cation part is substituted for Zn-formed MeZnO (Me = Be, Mg, Cd, etc.), and the solid solubility of Me is limited. In theory, there are few reports on the solid solution properties of the II-VI ternary alloy. In this paper, the thermodynamic properties of CdxZn1-xO, BxZn1-xO, MgxZn1-xO, CdO1-xSx and ZnS1-xSe and other II-VI ternary alloy solid solutions are studied by the first principle calculation and the group expansion method. The formation energy and phase diagram of CdxZn1-xO, BxZn1-xO, MgxZn1-xO, CdO1-xSx and ZnS1-xSx are analyzed. The main contents and conclusions are as follows: (1) The formation energy and phase diagram of wurtzite (WZ) and rock salt (RS) CdxZn1-xO ternary alloy are calculated. The formation energy of most of the CdxZn1-xO alloy configurations was found to be greater than zero by the formation of energy, indicating that ZnO and CdO were difficult to combine to form a solid solution at low temperatures. Two metastable phase structures of the WZ-CdxZn1-xO alloy (Cd1/ 3Zn2/ 3O and Cd2/ 3Zn1/ 3O) were further calculated. The lattice constants a and c, the bond length, the O-Zn (Cd)-O bond angle and the electronic structure of the two metastable phases of Cd1/ 3Zn2/ 3O and Cd2/ 3Zn1/ 3O are found, and the lattice constants a and c are gradually increased with the increase of the content of Cd in the WZ-CdxZn1-xO alloy, but the ratio c/ a of the lattice constant is gradually reduced. Similarly, with the increase of Cd doping, the size of the O-Zn (Cd)-O bond and the band gap are gradually reduced. The effective group interaction coefficient of wurtzite and the structure of CdxZn1-xO is calculated and analyzed, and the group of two atoms is found to be dominant in the effective group interaction coefficient, indicating that the two-atom group has the greatest contribution to the formation energy. By calculating the two-phase phase diagram of the WZ-CdxZn1-xO and RS-CdxZn1xO alloys, the solid solubility of Cd in WZ-ZnO at 1600 K was 0.13, but the solid solubility of Zn in the RS-CdO was 0.01. (2) The formation energy and the thermodynamic phase diagram of wurtzite and sphalerite structure (ZB) BexZn1-xO were calculated. The formation energy of most of the BexZn1-xO alloy configurations was found to be greater than zero by the formation of energy, indicating that ZnO and BeO were difficult to combine at low temperature to form a solid solution. The effective group interaction coefficient calculation of WZ-BexZn1-xO and ZB-BexZn1-x shows that, for the WZ-BexZn1-xO, the group of the two atoms and the four atoms take the leading role in the effective group interaction coefficient, indicating that the group of the two atoms and the four atoms has the greatest contribution to the formation energy. For ZB-BexZn1-xO, the two-atom group is dominant in the effective group interaction coefficient, indicating that the two-atom group has the greatest contribution to the formation energy. The phase diagram of wurtzite and sphalerite BexZn1-xO shows that the phase diagram of wurtzite and sphalerite BexZn1xO has a great effect on the phase diagram of wurtzite and sphalerite. The lattice vibration has a great influence on the solid solubility of Be (Zn) in ZnO (BeO). (3) The formation energy and the thermodynamic phase diagram of the MgxZn1-xO alloy of wurtzite and rock salt are calculated. By calculating the formation energy of MgxZn1-xO, it is found that the formation energy of most of the MgxZn1-xO alloy configuration at low temperature can be less than zero, indicating that ZnO and MgO are easy to bond to form a solid solution at low temperature. The effective group interaction coefficients of wurtzite and halite structural MgxZn1-xO were also calculated. For MgxZn1-xO by the effective group interaction coefficient, the group of two atoms is dominant in the effective group interaction coefficient, indicating that the two-atom group has the greatest contribution to the formation of the MgxZn1-xO. The two-phase phase diagram of WZ-MgxZn1-xO and RS-MgxZn1-xO has found that Mg is hard to be dissolved in the wurtzite type ZnO, and the Zn is more easily soluble in the MgO of the rock salt ore structure. (4) The formation energy and the thermodynamic phase diagram of wurtzite and halite structure CdO1-xSx are calculated. By calculating the formation energy of CdO1-xSx, the formation energy of most of the CdO1-xSx alloy configurations is found to be greater than zero, indicating that CdO and CdS are difficult to combine to form a solid solution at low temperatures. The effective group interaction coefficients of wurtzite and halite structures, CdO1-xSx, are also calculated. The two-atom group is dominant in the effective group interaction coefficient, indicating that the two-atom group has the greatest contribution to the formation of the CdO1-xSx. The two-phase phase diagram of WZ-CdO1-xSx and RS-CdO1-xSx was calculated and analyzed. (5) The thermodynamic properties of the formation energy and phase diagram of WZ-ZnS1-xSx and ZB-ZnS1-xSx are studied. By calculating the formation energy of ZnS1-xSx of wurtzite and sphalerite structure, the formation energy of most of the ZnS1-xSx alloy configurations is found to be greater than zero, indicating that ZnS and ZnSe are difficult to combine to form a solid solution at low temperature. The analysis of the effective group interaction coefficient shows that the group of two atoms is dominant in the effective group interaction coefficient, indicating that the two-atom group has the greatest contribution to the formation energy. The x-T phase diagram of ZnS1-xSx alloy is calculated and analyzed. It is found that the solid solubility of Se in ZnS is substantially the same as that of S in ZnSe, whether wurtzite structure or sphalerite structure alloy. For the above-mentioned semiconductor alloy of the five systems, the formation energy calculated by the expansion method of the group and the formation energy calculated by the first principle are basically the same, so that the validity and the feasibility of the formation energy of the alloy are calculated by the method of the group expansion.
【学位授予单位】：湖北大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN304

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