Transient photoresponse and incident power dependence of high-efficiency germanium quantum dot photodetectors

We report a systematic study of time-resolved and power-dependent photoresponse in high-efficiency germanium quantum dot photodetectors (Ge-QD PDs), with internal quantum efficiencies greater than 100% over a broad wavelength, reverse bias, and incident power range. Turn-on and turn-off response times (tau(on) and tau(off)) are shown to depend on series resistance, bias, optical power, and thickness (W-QD) of the Ge-QD layer, with measured tau(off) values down to similar to 40 ns. Two different photoconduction regimes are observed at low and high reverse bias, with a transition around -3 V. A transient current overshoot phenomenon is also observed, which depends on bias and illumination power.