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The growth conditions of two types of indium-based III-V nanowires, InP and InN, are tailored such that instead of yielding conventional wire-type morphologies, single-crystal conical structures are formed with an enlarged diameter either near the base or near the tip. By using indium droplets as a growth catalyst, combined with an excess indium supply during growth, "ice cream cone" type structures are formed with a nanowire "cone" and an indium-based "ice cream" droplet on top for both InP and InN. Surface polycrystallinity and annihilation of the catalyst tip of the conical InP nanowires are observed when the indium supply is turned off during the growth process. This growth design technique is extended to create single-crystal InN nanowires with the same morphology. Conical InN nanowires with an enlarged base are obtained through the use of an excess combined Au-In growth catalyst. Electrochemical studies of the InP nanowires on silicon demonstrate a reduction photocurrent as a proof of photovolatic behavior and provide insight as to how the observed surface polycrystallinity and the resulting interface affect these device-level properties. Additionally, a photovoltage is induced in both types of conical InN nanowires on silicon, which is not replicated in epitaxial InN thin films.

Two lattice-matched epitaxial III-V phosphide films of thicknesses between 400 and 500 nm are grown by metal-organic chemical vapor deposition: InGaP on GaAs and GaP on Si. These structures are designed as photocathodes for solar-driven chemical reduction processes such as the hydrogen evolution reaction (HER) and CO 2 reduction into higher-order hydrocarbons. By using p + substrates and undoped epitaxial layers, an extended space-charge active region is achieved in the electrode with a design analogous to a p-i-n solar cell. When in contact with the methyl viologen MV +/++ redox couple, the InGaP/GaAs and GaP/Si cathodes generate a photovoltage of 388 mV and 274 mV, respectively, under 1 sun illumination. Incident photon-to-current efficiency (IPCE) measurements confirm that the undoped active layers are exclusively performing light absorption and minority carrier diffusion-based charge transfer of high-energy photons. This shows that performance can be significantly boosted with lower-doped substrates. The InGaP/GaAs and GaP/Si electrodes are shown to drive the HER at saturation photocurrent densities of 9.05 mA/cm 2 and 2.34 mA/cm 2 , respectively, under 1 sun illumination without a co-catalyst and under a large reduction bias. Thicker films did not show a corresponding increased performance, and can be explained through understanding of crystalline defects and the electrostatics of the junctions.

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Despite a recent focus in developing energy harvesting technologies from a variety of sources, no work has been done in capturing blackbody radiation from the surrounding environment. This work aims to extend semiconductor-based solar energy harvesting into the infrared (IR) range of the electromagnetic spectrum so as to take advantage of this blackbody radiation. We have investigated the use of mercury cadmium telluride (HgCdTe) p-n junction devices in order to achieve this goal. A device simulation tool, named MCT-SIM, was developed in order to obtain the photovoltaic characteristics of P+/N-/N+ structures exposed to blackbody radiation and an applied voltage bias. An IR energy harvesting system was developed and evaluated with the use of this tool. When this system is exposed to blackbody radiation at a temperature of 300 K, it generates a series-limited photocurrent of 28.115 mA/cm 2 ; this value can be increased through further optimization. Subsequent analysis shows that performance limitations of this system are due to the presence of a large intrinsic carrier concentration and associated Auger effects within the absorbing layer of HgCdTe.