III-V Nanowires and Nanoneedles on Lattice Mismatched Substrates for Optoelectronic Device Applications

Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission. We believe that high-speed, low power consumption diode lasers and photodetectors directly integrated onto Si CMOS devices are key elements to high speed optical interconnects. Despite many years of research, integration of direct bandgap III-V compounds onto Si CMOS remains challenging. The bottleneck has been the process incompatibility of the two types of material systems. It is now widely accepted that optoelectronic devices should be fabricated on finished CMOS ICs to avoid these issues. One critical parameter is temperature – the temperature at which high-quality III-V materials can be grown needs to be low enough to sustain CMOS ICs. Another major challenge for the integration is the large lattice mismatch between III-Vs and Si. The large lattice mismatch results in a high misfit dislocation density for III-V thin films grown onto Si which largely degrades the crystal quality. In this dissertation, I will present III-V nanowires and nanoneedles which we successfully grew dislocation-free on Si and other kinds of lattice mismatched substrates with CMOS-compatible growth temperatures. The strain energy due to the lattice mismatch is relieved via elastic relaxation for these one-dimensional materials. For the Au-catalytic vapor-liquid-solid III-V nanowires on Si, the nanowires were grown at 430-470°C in a metal-organic chemical vapor deposition system. We observed that there existed a critical diameter for epitaxial nanowires grown on lattice-mismatched substrates, up to as large as 11.6% mismatch for InAs nanowires on Si. Below the critical diameter, well aligned nanowires with bright photoluminescence can grow, while above the critical diameter, spiky structures form. We report well aligned InP nanowires on Si with a very narrow photoluminescence linewidth of 1.4 meV, indicating excellent crystal quality. Regarding the growth parameter study, the precursor V/III ratio could be used to tailor the InP nanowire shape and the optical properties. For the catalyst-free GaAs-based nanoneedles, including InGaAs and AlGaAs materials, needles were successfully grown on GaAs, Si and sapphire substrates at 400°C. A typical 2 nanoneedle has a hexagonal cross section with a 6-9° taper angle, which results …