复杂不等价半导体合金有序和无序结构及新物性的研究

Complex nonisovalent semiconductor AX/BY alloys are consist of binary semiconducts AX and BY, where the effects of internal strains induced by the lattice mismatch on the alloying properties can be effectively eliminated. It is the A-Y or B-X bonds that make the alloys possess more novel functions than AX and BY, such as the visible-light absorption and the enhancement of piezoelectricity. As the important renewable energy materials, they have widely potential applications in the technological fields of solid-state lighting, solar cells, water splitting and piezoelectric devices and so on. In this owrk, we will systematically investigate the low-temperature ordered and high-temperature disordered structures of alloys to show the effects of structural odering on the physical properties and the ordered-disordered phase transition, from which the alloying composition-temperature phase diagrams are plotted. We will show the effects of lattice vibrations on the phase diagram and the miscibility-gap temperature by taking into account the vibrational entropy. Meanwhile, we will also adopt the metadynamics method to study the structural evolution of alloys induced by temperature and pressure to show the detailed evolutionary pathways and the stability of intermediate and end-point structures. Finally, we will calculate the dependence of band structure, piezoelectric response and other properties on the alloying composition, temperature and pressure, thus to point out the feasible ways to tune the band gap and to enhance the piezoelectricity, which will be helpful in widening their technological applications.

复杂不等价半导体AX/BY合金是由不等价二元半导体AX和BY形成的合金材料，能够有效减少晶格失配引起的内部应变对合金性质的影响，同时A-Y或B-X化学键可使其具有AX和BY所不具备的优异性能，如高效吸收可见光和良好的压电效应等。作为重要的可再生能源材料在固态发光照明、太阳能电池、光解水和压电器件等领域具有广阔的应用前景。本课题拟系统研究不等价合金的低温有序结构和高温无序结构，分析结构有序性对合金性质的影响和有序到无序的结构相变，得到组分与温度的相图。通过分析振动熵对合金稳定性的贡献，指出晶格振动效应对相图形状和不相混溶区温度的影响。采用动力学方法研究不同温度和压强作用下合金的结构演化，分析结构演化的具体路径、中间和终点结构的稳定性。在此基础上揭示能带结构和压电效应等性质与合金组分、温度和压强之间的定量关系，指出调节带隙和提高压电效应的有效方法，为扩展其在技术领域中的应用提供指导和参考。

针对目前半导体合金研究在构型和物理性质等领域中存在的问题，本项目主要研究半导体Cu-Ga-S和Cu-Ga-Se合金有序和无序结构、GaN-ZnO合金内建电场与电子结构之间的关系和3-9 BC3热输运等性质。主要研究结果分以下方面: (1)揭示了原子空位规则分布对有序结构稳定性的影响，画出了压强与组分的相图；(2)给出了实验合成温度与结构无序性之间以及无序性与光吸收系数之间的量化关系，指导实验工作得到特定的光学性质；(3)预测了一定厚度范围内稳定的8|4构型，指出其光吸收效率远高于常规六方构型，源于内建电场为零；(4)针对二维体系中的常见六角环构型提出了3-X模型，统一了对二维多三角形结构的认识。分析了3-9 BC3热导率与温度之间的反常线性关系以及对应的基本规律和驱动机理，指出原子共振引起的高群速度是反常效应的根源。以上研究结果和实验研究工作紧密相关，直接为实验提供理论指导，较好地完成了预期的研究目标，主要体现在以下方面:(1)指出如何调控实验合成温度和退火时间提高光吸收效率，且吸收频率在紫外到红外波段范围内；(2)通过8|4构型的结构预测和稳定性分析，指导该合金的实验合成，以此提高在可见光波段的吸收效率，促进在光催化或半导体发光领域中的应用；(3)指出反常热输运对应的总热导率通常较低，所以此类材料在散热器件中应用价值不大，改变了对此问题的已有认识。