Semiconductor photodetectors for photon-starved applications in the short-wavelength infrared spectral region

Abstract

The design, fabrication and characterisation of planar geometry Ge-on-Si single-photon avalanche diode (SPAD) detectors is described in this Thesis. These devices utilise a Si avalanche multiplication layer, and an adjacent Ge layer to absorb short-wave infrared incident photons. The innovative planar geometry design ensures the confinement of the high electric field to the centre of the detector away from the exposed sidewalls resulting in significantly reduced dark count rate (DCR). Planar Ge-on-Si SPADs were fabricated and characterised in terms of single-photon detection efficiency (SPDE), DCR, and timing jitter. These devices exhibited SPDE of almost one order of magnitude greater than previously reported, with the highest SPDE measured being 38%. The dark count rates per unit area were approximately 4 orders of magnitude less than equivalent mesa devices. A record-low noise equivalent power of 4 × 10-17 WHz-1/2 was obtained, more than two orders of magnitude lower than the previous best reported value. The lowest timing jitter of 26 µm diameter devices was 150 ps. These devices exhibited lower afterpulsing when compared to a commercial InGaAs/InP SPAD detector, illustrating the potential for high count rate operation. An investigation of an SPDE spectral dependence at different operating temperatures revealed that efficient single-photon detection of 1550 nm wavelength light will require an operating temperature of 245 K. Laboratory-based light detection and ranging (LIDAR) experiments using the time-offlight approach were performed using an individual Ge-on-Si SPAD detector. This approach allowed depth and intensity profiles of scanned targets to be reconstructed. Based on these results, a parametric LIDAR model was used to estimate LIDAR performance at long distances. For example, eye-safe sub-mW average laser power levels would be sufficient for imaging at kilometre distances. It was demonstrated that by employing appropriate image processing algorithms the total acquisition time can be reduced down to a few seconds for a 10000 pixels image at kilometre range, illustrating the potential for rapid three-dimensional imaging for automotive applications.