Growth and Properties of Epitaxial Semiconductor Films

外延薄膜生长包括将原子从蒸汽沉积到加热的单晶衬底上。原子在表面上自组装成晶层，这与衬底晶体的原子排列相一致。在这个研究项目中，我们将从光学或自旋电子器件的角度探索新型半导体和氧化物合金的外延薄膜的生长和性质。因为生长过程是在真空环境中进行的，所以我们可以在生长过程中利用电子衍射在原子尺度上监测表面结构，在亚微米尺度上通过光散射来监测表面结构。一种令人感兴趣的合金是含有III-V半导体GaAsBi.这种合金是高度失配半导体的一个例子，因为铋比镓或砷大得多。虽然Bi与As是等电子的，但其成键轨道的能量与As的能量有很大的不同，它的行为像一个杂质，并且强烈地扭曲了主体的电子结构。作为最重的V族元素和最重的非放射性元素，铋还具有最大的自旋轨道耦合，这进一步导致了不寻常的电子性质。GaAsBi可能会在发光器件或长波红外探测器中有未来的应用。其他感兴趣的材料是用于波导激光器的稀土掺杂蓝宝石薄膜，以及成分为II3-V2的一类相对未被开发的半导体。除了是一类鲜为人知的材料，有可能产生意想不到的新性能外，这些材料还包括半导体，如Ca3N2和Zn3P2，它们的禁带宽度在适合太阳能光伏应用的范围内，并且由无毒和丰富的元素组成。一种新的半导体材料的发现可能使人们有可能绕过现有光伏材料的问题，以低成本制造高效率器件，同时避免有毒和稀有元素。一种改进的薄膜光伏材料将对能源经济和碳排放产生巨大影响。这项研究计划涉及复杂的材料生长设备，这些设备将由研究生操作，作为他们培训的一部分。

Epitaxial film growth involves the deposition of atoms from a vapour onto a heated single crystal substrate. The atoms self-assemble on the surface into a crystalline layer, that is registered with the atomic arrangement of the substrate crystal. In this research program we will explore the growth and properties of epitaxial films of new semiconductor and oxide alloys that are promising from the perspective of optical or spintronic devices. Because the growth process takes place in a vacuum environment we can monitor the surface structure at the atomic scale using electron diffraction, and on the sub-micron scale by light scattering, during growth. One alloy of interest is the bismuth containing III-V semiconductor GaAsBi. This alloy is an example of a highly mismatched semiconductor, since Bi is significantly bigger than Ga or As. Although Bi is isoelectronic with As, the energy of its bonding orbitals is sufficiently different from As that it acts like an impurity, and strongly distorts the electronic structure of the host. As the heaviest group V element and the heaviest non-radioactive element, Bi also has the largest spin orbit coupling which further contributes to creating unusual electronic properties. The GaAsBi may have future applications in light emitting devices or long wavelength infrared detectors. Other materials of interest are rare earth doped sapphire films for waveguide lasers and a relatively unexplored class of semiconductors with the composition II3-V2. In addition to being a poorly understood class of materials with the potential for unexpected new properties, these materials include semiconductors such as Ca3N2 and Zn3P2 that have bandgaps in the right range for solar photovoltaic applications, and are made up of non-toxic and abundant elements. The discovery of a new semiconductor material might make it possible to bypass problems with current photovoltaic materials in making high efficiency devices at low cost while avoiding toxic and rare elements. The impact of an improved thin film photovoltaic material on the energy economy and carbon emissions would be huge. This research program involves sophisticated materials growth equipment that will be operated by graduate students as part of their training.