Evolution and prospects for single-photon avalanche diodes and quenching circuits

The evolution of solid-state avalanche detectors of single optical photons is outlined and the issues for further progress are discussed. Physical phenomena that underlay the operation of the single-photon avalanche diodes (SPAD) and determine the performance are considered and their role is assessed (detection efficiency; dark-counting rate; afterpulsing; photon timing resolution; etc.). The main technological issues that hamper the development of detectors with wide sensitive area and of array detectors with high filling factor are illustrated. Silicon SPADs are the main focus of attention; infrared-sensitive SPADs in germanium and in compound semiconductors are also dealt with. The role of the active-quenching circuits (AQC) is assessed and the evolution is outlined up to integrated AQCs, which offer the prospect of monolithic integration of complete photon counter instruments.