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A study of InP nanowires : growth, material properties, and application in optoelectronics


As society continues to push for devices that are faster, cheaper, and more efficient, new technology must find a way to meet this demand. Nanotechnology has become one of the most active fields of research to meet this growing need. Semiconductor nanowires have gained much attention over the course of the past decade. Their unique geometry leads to a large surface area to volume ratio, which has been exploited in many devices. High-quality nanowires have been grown from a variety of materials, including III -V and II-VI alloys, silicon, nitrides, oxides, and metals. The study of nanowires so far has focused on their growth, an understanding of their fundamental properties, as well as possible device applications. However, as with any new technology, there are still many questions that remain to be answered. The goal of this thesis is to expand the basic understanding of nanowires. A bottom up approach is used to accomplish this goal for the system of InP nanowires. First, a detailed explanation is given on how and why these InP nanowires grow. Unlike most nanowire systems, this growth does not involve a deposited catalyst. Instead, self-assembled indium droplets act as the nanowire nucleation sites. Optimized growth of this system provides samples with vertically aligned nanowires with uniform diameter and length. Details of the optimization of this growth are described. Second, a novel fabrication scheme is designed to measure the electrooptic properties of InP nanowires. A technique is created to remove the nanowires from their growth substrate and transfer them to a host substrate in a polymer while retaining their vertical alignment. This process allows for the measurement of their electrooptic coefficient. The nanowire electrooptic coefficient values show an improvement of one to two orders of magnitude enhancement when compared to bulk InP. Also, the figure of merit for the nanowire sample is up to a factor of twenty larger than lithium niobate, an industry standard electrooptic material. Finally, the viability of a polymer/nanowire hybrid solar cell is discussed. Nanowires are grown directly onto an electrode and are coated with a conductive polymer. Current-voltage measurements are carried out on this photodiode and as well as their response to illumination. Photodiodes with very good rectification, low reverse saturation current and good ideality factors are achieved. The response of the nanowire/polymer hybrid system to illumination is promising and can thus be seen as a possible alternative to current solar cell technology

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