It is well known that avalanche photodiode can enhance the signal to noise ratio of a detection system, when the excess avalanche noise is low. The excess noise factor, F which characterizes the excess noise of an APD can be calculated using the established noise theory from R. McIntyre. When the ratio of hole to electron ionization coefficients, k = 0, F ~2 is achieved at high gain. This means the avalanche gain, M, can be increased without the penalty of increased excess noise factor. In this work, we will present the progress in APDs incorporating InAs and AlGaAsSb as the avalanche regions. Both show k ~0 and therefore F~2. The former can be used for low photon detection at wavelengths beyond InGaAs, while the latter can be combined with InGaAs to provide low noise APD for wavelengths up to 1700 nm. Our work demonstrated that low photons of < 100 photon within a 50 microsecond pulse can be detected using InAs APDs. We also achieved single photon detection at 1550 nm using AlGaAsSb APD.
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