InAs avalanche photodiodes
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The ability to efficiently detect low-level light in the infrared above wavelengths of 1.7 μm is becoming increasingly important for many applications such as gas sensing, defence/geoscience ranging and clinical thermography. The III-V narrow gap semiconductor InAs, with a bandgap of 0.36 eV, is well known for its use as a conventional photodiode. The aim of this thesis was to design, build and test InAs devices for use as reverse biased avalanche photodiodes. In order to fabricate a lownoise detector, a passivation study was conducted. For the first time we report the achievement of high quality single crystal II-VI passivation layers on InAs mesa structures. Pre-growth surface oxide removal processes were developed to improve surface morphology of II-VI layers grown on InAs samples. ZnSe and ZnTe successfully terminate the InAs mesa devices preventing atmospheric oxidation. Low surface leakage currents are observed at low reverse bias and at room temperature for both materials. LIDAR at wavelengths greater than 2 μm was studied using these InAs mesa photodiodes, showing potential to take advantage of the low solar background at these wavelengths. For the first time, laboratory based LIDAR experiments, with ranges of around 0.5 metre stand-off distance, were performed with InAs n-i-p edge illuminated mesa photodiodes, used in linear multiplication mode. Time-of-flight measurements were demonstrated at wavelengths from 1.3 μm to 2.365 μm. A 6 mm ranging error was observed in these short range measurements.