III-V Nanowire-based Infrared Photodetectors : Design, Fabrication and Characterization

Sammanfattning: Semiconductors are the backbone of almost every electrical or optical component, one of them being photodetectors. Photodetectors are used in many applications such as digital cameras or solar panels. They can also be designed to detect the omnipresent infrared radiation, discovered in 1800, which is invisible to human eye. Such infrared photodetectors are commercially used in e.g. night-vision, optical communication, environmental monitoring and surveillance. With the advent of nanotechnology, the component size is shrinking rapidly, thus generating a need for new materials compatible with industrial standards. Nanowires possess all the ideal characteristics such as enhanced resonant absorption, tunable spectral response and possible heterogenous integration. This thesis reports on fundamental studies of different types of nanowire-based infrared photodetectors, ultimately designed for industrial applications. The first two studies focused on the influence of doping profile and segment lengths on the performance of p+-i-n+ InP nanowire array photodetectors. An increase in p+-segment length was found to significantly enhance the photocurrent by shifting the depletion region from the substrate far up into the nanowires. Moreover, it was shown that a low doping at the tip of the nanowires made it possible to tune the detector window with an applied bias. A key advantage of nanowires is the possibility to fabricate quantum heterostructures. Broad near-infrared detection was demonstrated in a subsequent study by incorporating multiple InAsP quantum discs in InP n+-i-n+ nanowire array detectors. In low-light conditions, or in applications requiring large bandwidth, an enhanced photocurrent signal is desirable. The last study of the thesis reports on the realization of a spatially separated InAsP absorption region, optimized at 1.55µm for optical communication applications, combined with an InP multiplication region, all integrated in a single nanowire.Summarized, this thesis demonstrates the great promise held by nanowires for future photodetectors.