Scanning Tunneling Spectroscopy Studies of Transition Metal Oxides and Spin Light Emitting Diode Studies
Hatch, John B.
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Studies of three transition metal oxide (TMO) materials and two types of spin light emitting diodes (LEDs) are contained in this dissertation. The studies of the samples processed into spin LEDs contained herein were all grown with molecular beam epitaxy (MBE), and utilize the same spin injector material, manganese arsenide (MnAs). We have demonstrated that MnAs is an efficient spin injector of spin polarized electrons into gallium arsenide (GaAs) and indium arsenide (InAs). It has also been shown that annealing MnAs grown on GaAs does not cause Mn ions to diffuse into GaAs; such diffusion would be detrimental to spin injection. A scanning tunneling spectroscopy (STS) modulation bias technique was used to examine and spatially map the local density of states (LDOS) of the surfaces of these TMOs with sub-nanometer resolution. Two of the TMO materials have possible photovoltaic/photocatalytic applications, while the other undergoes a metal-insulator transition (MIT) and is a promising material for high-speed field effect transistors. The distributions of energy gaps measured across the surface of the two solar materials were found to be consistent with their respective absorption measurements. This confirms that the utilization of the successful co-doping scheme/alteration of the growth parameters effectively reduced the energy gaps thereby increasing the solar efficiency of these materials. Also, the electronic structure of an intermediate metallic phase was measured with STS for the first time to our knowledge in the MIT TMO material examined herein.