Growth and Properties of III-VI Based Heterostructures

9801302本项目的重点是III-VI基半导体的异质外延生长以及相关的结构和光学性质。III-VI材料主要包括两类：层状材料，如GaS和InSe，以及立方材料，如Ga2Se3和In2Se3，它们正在作为不同材料异质外延的原型系统进行研究，并可能成为电子或光电器件的新型材料。这两类III-VI材料在光学范围和与更传统的电子材料的化学兼容性上都有带隙。III-VI半导体的结构赋予了它们高度各向异性的输运、机械和光学性质以及很大的非线性极化率。具体目标是：通过分子束外延(MBE)确定GaS、Ga2Se3及相关材料的生长机制；确定衬底相互作用和表面键特性在控制GaxSey化合物成核和生长中的作用；建立一个实验和理论框架，以确定获得III-VI材料最佳结构、电子和光学性能的适当生长条件；通过对基本结构、电子和光学性质的分析，评估将这些材料用于新型光电子应用的可行性。重点研究了GaS和Ga2Se3在Si、GaAs、CaF2和A1203衬底上的成核和生长，以及所形成的薄膜的性质。将采用光电子能谱和非原位实验探针相结合的方法，包括光电子能谱和衍射、电子衍射、光学光谱、原子力显微镜和高分辨率电子显微镜，并结合生长过程的动力学模拟。衬底中的离子作用、表面钝化程度以及与覆盖层的固有晶格失配将在这四种材料中有所不同。该项目解决了材料科学中具有很高潜在技术相关性的主题领域的基础研究问题。这项研究将在基础水平上为电子/光子器件的新方面贡献基本的材料科学知识。现在可以使用实验工具对基本的表面过程进行原子水平的观察，如果更好地了解这些过程，就可以推动基础科学和技术的进步。从研究中获得的基本知识和理解有望为设计和生产改进的材料和材料组合提供基本的理解和基础，从而有助于提高先进器件和电路的性能和稳定性。该计划的一个重要特点是通过在一个具有根本意义和技术意义的领域对学生进行培训，将研究和教育结合起来。***

9801302 Olmstead This project focuses on the heteroepitaxial growth of III-VI based semiconductors and on interrelated structural and optical properties. The III-VI materials comprise two principal classes: layered materials, such as GaSe and InSe, and cubic materials such as Ga2Se3 and In2Se3, which are being investigated as prototype systems for heteroepitaxy of dissimilar materials and as possible novel materials for electronic or optoelectronic devices. Both classes of III-VI materials have bandgaps in the optical range and chemical compatibility with more traditional electronic materials. The structure of III-VI semiconductors gives them highly anisotropic transport, mechanical and optical properties and large non-linear susceptibilities. Specific goals are: to determine growth mechanisms for GaSe, Ga2Se3 and related materials by molecular beam epitaxy (MBE); to determine the role of substrate interactions and surface bond character in controlling the nucleation and growth of GaxSey compounds; to establish an experimental and theoretical framework for determining the appropriate growth conditions to obtain optimal structural, electronic and optical properties in III-VI materials; to evaluate the feasibility of using these materials for novel opto-electronic applications through analysis of fundamental structural, electronic and optical properties. The approach is to concentrate on the nucleation and growth of GaSe and Ga2Se3 on Si, GaAs, CaF2 and A1203, and on the properties of the resultant thin films. A combination of in situ and ex situ experimental probes including photoelectron spectroscopy and diffraction, electron diffraction, optical spectroscopy, atomic force microscopy, and high resolution transmission electron microscopy in combination with kinetic modeling of the growth process will be employed. The role of ionicity in the substrate, the degree of surface passivation, and the inherent lattice mismatch with the overlayer will be varied among t he four materials. %%% The project addresses basic research issues in a topical area of materials science having high potential technological relevance. The research will contribute basic materials science knowledge at a fundamental level to new aspects of electronic/photonic devices. Experimental tools are now available to allow atomic level observation of elementary surface processes which when better understood allow advances in fundamental science and technology. The basic knowledge and understanding gained from the research is expected to contribute to improving the performance and stability of advanced devices and circuits by providing a fundamental understanding and a basis for designing and producing improved materials, and materials combinations. An important feature of the program is the integration of research and education through the training of students in a fundamentally and technologically significant area. ***