UC San Diego

III-V nanowires (NWs) have in recent years attracted an increasing research interest owing both to their interesting fundamental properties and to the prospect of numerous potential applications in electronics, optoelectronics, and photovoltaic. Dilute nitride NWs is a group of novel semiconductor material in which small amounts of N atoms substrate group V elements in conventional III-V semiconductor. With the advantage of free of lattice mismatch constraints and high absorption coefficients, III-N-V NWs is a group of promising yet little-studied material for solar cell applications. As a first step towards III-N-V NW solar cells on Si, the goal of this dissertation is to optimize the growth conditions of different NWs including on arbitrary substrate, patterned substrate and core-shell NWs.

The dissertation is divided into three major parts. In the first part, we report epitaxial growth of dilute nitride GaNAsP nanowires (NWs) and GaAsP/ GaNAsP core–shell nanowires on Si (111) by a self-catalyzed method. Growth windows, structural properties are investigated. The structural properties and optical properties are characterized using SEM, photoluminescence (PL), EDX etc. The properties of GaAs/GaNAsP nanowires demonstrates that alloying GaAsP with nitrogen represents a viable and attractive approach of bandgap engineering, which allows efficient tuning of the electronic properties of the GaNAsP NWs as required for future optoelectronic and photonic applications.

The second part demonstrates the successful growth of GaAs/GaNAs core/shell nanowires on patterned Si substrate. The micro-PL and Transmission electron microscopy characterization results show good crystal structure of nanowires and minimal defects. The study illustrates the feasibility of the epitaxial growth of patterned GaAs with dilute nitride shells on Si substrates, which would have potential for Si-friendly intermediate band solar cells and telecom emitters.

In the last part, single pin-GaNP/GaNP/GaNP core/shell nanowires solar cell is fabricated utilizing e-beam writing technique. The metal contact is deposited by e-beam evaporation. The characteristic circuit current-voltage curve is measured and the performance of single nanowire solar cell is analyzed.