Growth and Properties of Epitaxial Semiconductor Films

外延薄膜的生长涉及原子从蒸汽沉积到加热的单晶衬底上。原子在表面自组装成晶体层，这与衬底晶体的原子排列一致。在本研究计划中，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外延膜的生长和性能。由于生长过程是在真空环境中进行的，我们可以在原子尺度上使用电子衍射来监测表面结构，在生长过程中使用光散射来监测亚微米尺度的表面结构。一种感兴趣的合金是含铋的III-V半导体GaAsBi。这种合金是高度不匹配的半导体的一个例子，因为Bi明显大于Ga或As。虽然Bi与As是等电子，但它的成键轨道的能量与As有很大的不同，它的行为就像一种杂质，并且强烈地扭曲了宿主的电子结构。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，这进一步有助于创造不同寻常的电子性质。GaAsBi在发光器件或长波红外探测器中具有广泛的应用前景。其他令人感兴趣的材料是用于波导激光器的稀土掺杂蓝宝石薄膜，以及一类成分为II3-V2的相对未开发的半导体。除了是一类鲜为人知的材料，具有意想不到的新特性的潜力之外，这些材料包括半导体，如Ca3N2和Zn3P2，它们的带隙在太阳能光伏应用的合适范围内，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会绕过目前光伏材料的问题，以低成本制造高效率的设备，同时避免有毒和稀有元素。改进的薄膜光伏材料对能源经济和碳排放的影响将是巨大的。这个研究项目涉及复杂的材料生长设备，将由研究生操作，作为他们训练的一部分。

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.