High current InP/InGaAs evanescently coupled waveguide phototransistor

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 Al_xIn_(1-x-y)Ga_yAs 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.