UCLA

The research in this dissertation attempts to take advantage of the nanowire platform in order to outperform state-of-the-art commercial detectors in one or more metrics. Nanowire photodetectors with increasing cutoff wavelength and device complexity will be presented, beginning with simple GaAs homojunction photodetectors. It is shown that through proper design, an ideality factor of 𝑛=1.0−1.15 and dark current density as low as 𝐽=6�10−7 A/cm2 can be achieved, both equivalent to the best bulk GaAs diodes. The design principles learned from this study are applied to all of the nanowire photodetectors that follow. InGaAs-GaAs heterojunction photodetectors exhibit 𝑛=1.06 and a responsivity of up to 30 A/W, indicating avalanche gain. InGaAs avalanche photodetectors are shown to have low excess noise with 𝑘=0.15 and a bandwidth of 2.4 GHz. InGaAs-GaAs single photon avalanche diodes are operated in free-running mode with an ultra-low dark count rate of less than 60 Hz, a photon count rate of 8 MHz, and a timing jitter less than 38 ps. Free-running mode operation is possible through the control of afterpulsing through single nanowire avalanche pulses, with a maximum afterpulsing probability less than 25%. Finally, InAsSb-InAs heterojunction photodetectors are presented with an absorption cutoff at 3.0 μm and a maximum quantum efficiency of 29%. This work shows that for most photodetectors operating in the near-infrared, the nanowire platform can either match or surpass conventional planar photodetector performance, and in the case of single photon detectors, provides a compelling case for the commercialization of nanowire-based photodetectors.