Growth and Properties of Epitaxial Semiconductor Films

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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.