Abstract
We demonstrate by measurement and analysis that previously reported InP/InGaAs heterojunction phototransistors are promising photodetectors for long-wavelength optical receivers. The gain characteristics of these devices are shown to reflect the benefit of a wide band-gap emitter as well as the effects of recombination centers near the base-emitter heterojunction. In order to analyze the noise characteristics we derive a model which accounts for the three principal noise sources: the shot noise of the base current, the shot noise of the collector current, and the thermal noise of the load resistor. Using this model and experimental device parameters, we calculate the sensitivity of an optical receiver which utilizes a heterojunction phototransistor. This calculation indicates that the performance of this monolithic device can be as good as or exceed that of a hybrid p–i–n photodiode/field effect transistor-preamplifier combination.
Published Version
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