Ultrafast and highly efficient resonant cavity enhanced photodiodes
In this talk, we will review our research efforts on resonant cavity enhanced (RCE) high-speed high-efficiency photodiodes (PDs) operating in the 1st and 3rd optical communication windows. Using a microwave compatible planar fabrication process, we have designed and fabricated GaAs and InGaAs based RCE photodiodes. For RCE GaAs Schottky type photodiodes, we have achieved peak quantum efficiencies of 50% and 75% with semi-transparent (Au) and transparent (indium-tin-oxide) Schottky layers respectively. Along with 3-dB bandwidths of 50 and 60 GHz, these devices exhibit bandwidth-efficiency (BWE) products of 25 GHz and 45 GHz respectively. By using a postprocess recess etch, we tuned the resonance wavelength of an RCE InGaAs PD from 1605 to 1558 nm while keeping the peak efficiencies above 60%. The maximum quantum efficiency was 66% at 1572 nm which was in good agreement with our theoretical calculations. The photodiode had a linear response up to 6 mW optical power, where we obtained 5 mA photocurrent at 3 V reverse bias. The photodetector had a temporal response of 16 psec at 7 V bias. After system response deconvolution, the 3-dB bandwidth of the device was 31 GHz, which corresponds to a bandwidth-efficiency product of 20 GHz.