【作者】 李丹；

【导师】 张幸红；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2013， 博士

【摘要】 光电材料由于具有光子材料的先进性和电子材料的稳定性等特点，在微电子、光电子以及通信等高科技领域有着广泛的应用前景。因此，研究光电材料的电光性能在光电器件的设计和制造中就显得尤为必要。光电材料的电学性能和光学性能通常由能带结构、态密度以及各种光学常数来表征。目前光电材料的发展，正向着多元化和合金化的方向发展。但是由于化学成分的增加，使得在实验中不易获得满足化学计量比的晶体样本，而且不断增加的自由度也使材料的性质变得异常复杂，因此难以准确地测得材料的性质。利用基于密度泛函理论的第一性原理计算方法对材料进行模拟，不但能够准确分析现有材料的结构以及各种性能，甚至还能对尚未发现的新材料的光电性能进行预测。本论文主要研究了目前广泛流行的新型多元光电材料，包括三元半导体CuAlSe₂和CuAl₅Se₈、四元半导体I₂-II-IV-VI₄以及三元合金半导体AlxGa1-xN。在论文中首先简要介绍了这些新型光电材料在光电子器件领域的发展，同时介绍了本论文涉及的计算方法，在此基础上介绍了本论文的主要研究内容，具体内容和结论如下：首先在缺陷稳定性分析的基础上，利用第一性原理缺陷研究方法研究了包含一个(2V_Cu^-+Al_Cu⁺²)缺陷对的CuAl₅Se₈半导体材料的缺陷形成能，证明了该缺陷对存在的可能性。然后对缺陷半导体CuAl₅Se₈的六个弹性常数进行了研究，结果表明该晶体满足四角晶系的Born稳定性标准。通过能带结构以及态密度的分析表明， CuAlSe₂和CuAl₅Se₈都是直接带隙的半导体材料，而且缺陷晶体的带隙大于完整晶体。此外，通过介电函数、吸收光谱和反射率光谱的分析，研究了CuAlSe₂和CuAl₅Se₈的光学性能。提出了在0⁴.5eV的能量范围内，CuAl₅Se₈的光学跃迁幅度总是比CuAlSe₂的小。同时相对于完整结构，CuAl₅Se₈的吸收系数和反射率光谱均发生了蓝移，光谱的幅值也因价带顶附近Cu的3d态的减少而发生了下降。以上分析表明，无论是在电子结构还是光学性能上，缺陷对对材料都产生了较大的影响。然后利用第一性原理方法对三种不同结构的四元化合物半导体I₂-II-IV-VI₄的几何结构、电子性能和光学性能进行了研究，具体如下：（1）通过对含有V_Cu和Cu_Zn缺陷的锌黄锡矿结构的Cu₂ZnSnS4的缺陷稳定性进行分析，发现这两种点缺陷之间的形成能差别很小，从理论上证明了两种缺陷在晶体中是共存的。同时研究了Cu₂ZnSnS₄以及包含缺陷结构的晶体的电子结构，发现低浓度的缺陷并不能完全改变材料的性能。（2）还预测了黄锡矿结构的Cu₂CdGeSe₄和纤维锌矿-黄锡矿结构的Ag₂HgSnSe₄的电子结构和光学性能。（3）综合三种不同结构的四元材料的特性，可以得出如下结论： I₂-II-IV-VI₄族材料都是直接带隙的半导体，价带顶和导带底都位于布里渊区的Γ点。价带顶均由I族原子的d态和VI族原子的p态决定，导带底则由IV族原子的s态和VI族原子的p态所决定。最后本文讨论了Al的浓度和压力对闪锌矿结构的Al_xGa_1-xN合金材料性能的影响。电子结构分析的结果表明，随着Al浓度的增加合金的带隙从直接带隙转变为间接带隙（x=0.62）。同时为了进一步了解分子中原子的成键情况，还对闪锌矿结构的AlGaN合金Mulliken电荷布居分布进行了研究，结果表明晶体具有共价键的特征，其中Al-N键之间的共价性要比Ga-N键强。除此之外，随着Al浓度的增加材料的所有的光学峰均向高能量范围迁移，这是由于导带边缘的蓝移所造成的。通过不同压力下直接和间接带隙的变化，表明AlGaN合金材料在0¹5GPa的压力范围内保持闪锌矿结构不变，且带隙随压力的增加而不断增大。为了验证理论预测的正确性，本文还将理论结果与我们和前人的实验结果进行了对比，实验结果包括利用XRD对物相结构进行研究分析，以及利用椭偏仪和分光光度计对材料的电子和光学特性进行研究，发现实验结果和计算结果相当吻合，为理论研究奠定了坚实可靠的理论基础。更多还原

【Abstract】 For having the characteristics of photonic materials advance and electronicmaterials stability, photoelectric materials has a broad application prospect inmicroelectronics, photoelectron, communication technology and other high-techfield. Therefore, investigation on the electro-optical properties of optoelectronicmaterials in optoelectronic devices design and manufacture is particularly necessary.The electronic and optical properties of photoelectric materials are characterized bythe band structure, density of states and all kinds of optical constants. Now theinvestigation of photoelectric materials is focused on the diversification and alloy.However, the increased component makes it not easy to obtain a stoichiometric ratioof crystal sample in experiment, and the increment of the degrees of freedom alsomeans that the properties of these materials become more complex, which makes itdifficult to accurately measure the properties of material s. Based on the densityfunctional theory, the materials properties were simulated using the first-principlesmethod. This method could accurately get the information of the structures andvarious properties of the existing materials, and even could predict the photoelectricproperties of new materials.In this paper, the current popular new multiple photoelectric materialsincluding ternary semiconductors CuAlSe₂and CuAl₅Se₈, quaternarysemiconductors I₂-II-IV-VI₄and ternary alloy semiconductor AlxGa1-xN are studied.First, it gives a brief introduction of the development of these novel photoelectricmaterials in the fields of optoelectronic devices. And at the same time the simulationmethods used in the study are introduced. On these bases, the main research contentswere summarized. The contents and conclusions are as follows:Firstly, on the basis of analysis of the defect stability, the defect formationenergy of defect pair (2V_Cu^-+Al_Cu⁺²) in CuAl₅Se₈is studied using first-principlesmethods and the result proves that this defect pair maybe exist. Then the six elasticconstants of CuAl₅Se₈are investigated and it could found that the results satisfiedwith the Born stability criteria for tetragonal chalcopyrite structure. The analysis ofthe energy band structures and density of states shows that CuAlSe₂and CuAl₅Se₈are the direct gap materials, and the band gap of the defect crystal is bigger than thatof the perfect one. In addition, the optical properties are also studied by calculationsof the dielectric function, absorption spectra, and reflectivity of CuAlSe₂andCuAl₅Se₈. From these results we proposed that the amplitudes of the opticaltransitions for CuAl₅Se₈are always smaller than those of CuAlSe₂in the range of0⁴.5eV. Compared with the perfect crystal, the spectra including absorption coefficient and reflectivity for the defect crystal have a blue-shift. And theabsorption coefficient and reflectivity for CuAl₅Se₈also decreased with the decreaseof Cu3d states near the valence band maximum. The above analysis show that thedefect pair could affect the electronic structure s and optical properties of materials.Moreover, the geometric structures, electronic and optical properties of thequaternary semiconductor compounds I₂-II-IV-VI₄in three different structures arestudied using first-principles methods, the specific contents are as follows:（1） Byanalyzing the defect stabilities of V_Cu and CuZnin kesterite Cu₂ZnSnS4, we foundthat the difference of formation energy between these two point defects is very smalland then they can coexist in the Cu₂ZnSnS₄crystal. From the electronic structures ofCu₂ZnSnS4and the defect semiconductors we found that low concentration defect ofCuZnor VCucould not change the properties of material completely.（2） Theelectronic structures and optical properties of stannite-type Cu₂CdGeSe₄andwurtzite-stannite-type Ag₂HgSnSe₄are also predicted.（3） From the calculatedproperties of the above three quaternary materials, the following conclusions can bedrawn: I₂-II-IV-VI₄are all the direct gap semiconductors, and both the valence bandmaximum and the conduction band minimum exist at Γ point in the Brillouin zone.The valence band maximum is mainly dominated by the I d and VI p states, whilethe conduction band minimum is dominated by IV s and VI p states.Finally, the influence s of Al concentration and pressure on the properties ofzinc-blende AlxGa1-xN alloys are discussed as well. The results of the electronicstructures show that the band gap energy changes from the direct to indirect with theincrease of Al mole fraction（x=0.62）. In order to understand the bonding behaviorbetween atoms ulteriorly, the Mulliken charge populations are also studied forzinc-blende AlGaN alloys. The result shows that the alloys have covalent nature andthe covalent bonding strength of the Al-N bond is stronger than the Ga-N bond. Inaddition, due to the blue-shift of conduction band edge, all the optical peaks ofalloys have a tendency of shifting to the higher energy with the increase of Alconcentration. We also analyze the direct and indirect band gaps for alloys underdifferent pressures. The results show that AlGaN alloys keep zinc-blende structurewithin the pressure range of0¹5GPa, and the band gap increases with theenhancement of the pressure.In order to verify the correctness of the theoretical predictions, the theoreticalresults have been compared with our and previous experimental results. The phasestructure s of thin films are investigated and analyzed by XRD. And the electricaland optical properties of these films are investigated by ellipsometry andspectrophotometry. We found that the experimental results are in good agreement with the calculated results. It laid a solid and reliable theoretical foundation fortheoretical research.更多还原