An evanescently coupled side-illuminated waveguide phototransistor to improve on power handling and coupling efficiency over vertically illuminated photodetectors was demonstrated. The Al composition in the AlxIn(1-x-y)GayAs passive waveguide was tailored for optimised optical confinement and coupling into the InGaAs absorption region. The presence of a passive waveguide as well as the internal transistor gain in the waveguide phototransistor showed an improvement in responsivity that was 300 times more than a p-i-n diode of similar structure to the base–collector junction.
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Ng et al. (2005) studied this question.