In a suitably cooled and biased semiconductor diode, individual photoevents will trigger avalanche discharges which can be detected and quenched by external circuitry. The resulting triggeredhyphen;avalanche detector (TAD) is a solidhyphen;state analog of the Geiger counter, and can be used to detect individual visible and infrared photons. TAD operation in commercially available silicon avalanche photodiodes was found to be limited by carrierhyphen;trapping effects to a noisehyphen;equivalent power (NEP) of 7times;10minus;16WHzminus;1/2for continuous signals at 0.8hyphen;mgr;m wavelength, but can achieve 7times;10minus;18WHzminus;1/2for optimally pulsed signals. Interfering avalanches triggered by trapped carriers have been used to investigate exactly those traps which affect TAD operation in a given diode structure and material. Substantial NEP improvement is possible in diodes optimized for TAD operation. The usual requirement for disparate carrier ionization rates in avalanche diode materials does not apply to TAD operation, and a wide range of narrowhyphen;bandhyphen;gap materials can be considered for infrared photonhyphen;counting detectors.
展开▼
