High bandwidth surface-illuminated InGaAs/InP uni-travelling-carrier photodetector

Uni-traveling-carrier photodiodes(UTC-PDs)with ultrafast response and high saturation output are reported.A gradient doping layer and a narrow InP cliff layer were introduced to enhance the saturation and bandwidth characteristics.We measured the dark current,photo response,bandwidth,and saturation current of the fabricated UTC devices.For a15-μm-diameter device,the dark current was 3.5 nA at a reverse bias of 1 V,and the 3-dB bandwidth was 17.2 GHz at a reverse bias of 5 V,which are comparable to the theoretically values.The maximum responsivity at 1.55μm was 0.32 A/W.The saturation output current was over 19.0 mA without bias.