Sb-based avalanche photodiodes and single photon avalanche photodiodes

Avalanche Photodiodes (APDs) and Single-Photon Avalanche Diodes (SPADs) have become increasingly critical as the expansion of applications, such as LiDAR, gas sensing, and Quantum Key Distribution (QKD) - requires precise low photon level detection. In recent years, AlGaAsSb on InP has demonstrated superior noise characteristics and temperature-independent performance.
This thesis firstly focuses on the characterisation of InGaAs/AlGaAsSb Separate Absorption and Multiplication (SAM) APDs for operation above room temperature. The results indicate that these devices can potentially operate at elevated temperatures while maintaining sub-100 photon detection capabilities. Furthermore, the similar thermal coefficient of breakdown voltage (Cbd) observed at higher temperatures (Room temperature to 95 °C) – matching those measured at lower temperatures – suggests a broader operational range than may not require thermal stabilisers.
Secondly, the temperature dependence of SPAD performance was investigated using improved InGaAs/AlGaAsSb SPADs. The findings demonstrate a significant increase in Single Photon Detection Efficiency (SPDE) compared to our previous generation SPAD. However, the dark count rate (DCR) remained limited by tunnelling from the narrow-bandgap InGaAs region. A proposed InGaAs/AlGaAsSb SPAD design is presented; simulations suggest that if the tunnelling is mitigated, the DCR performance will align with state-of-the-art InGaAs/InP SPADs.
Finally, motivated by the inefficient detection of InGaAs APD at Mid-Wave Infrared (MWIR) wavelength, this work explores the design of an InAs-based SAM-APD. AlInAsSb is a promising candidate due to the low noise performance and temperature stability previously demonstrated on GaSb systems. The avalanche gain and excess noise factor on two pairs of Al0.7InAsSb p-i-n and n-i-p APDs that lattice matched to InAs were characterised. The results show that Al0.7InaAsSb is an electron-dominant impact ionisation material with a k-value of 0.1. Although the excess noise performance is not as low as Al0.8InAsSb, its direct and smaller bandgap potentially simplifies the bandgap grading for InAs/AlInAsSb SAM-APDs.