This project aims to demonstrate semiconductor nanowire based infrared avalanche photodetectors (APDs) with ultra-high sensitivity towards single photon detection. By employing the advantages of their unique one-dimensional nanoscale geometry, the nanowire APDs can be engineered to different device architectures to achieve performance superior to their conventional counterparts. This will contribute to the development of next generation infrared photodetector technology enabling numerous emerging fields in modern transportation, communication, quantum computation and information processing.