Fast and efficient germanium quantum dot photodetector with an ultrathin active layer

An ultrathin layer (13 nm) of germanium (Ge) quantum dots embedded in a SiO2 matrix was deposited on a Ge substrate for photodetection in both the visible and near-infrared (IR). Operated at T = 150 K, the device exhibits higher than 10(5)% internal quantum efficiency (IQE) at a reverse bias of -1.3 V under low light conditions (< 30 nW) at both lambda = 640 and 1550 nm. The transient response of 640 nm pulses stays below 15 ns for both rise and fall times; the IR response is only slightly slower. Our work demonstrates a high-performance broadband photodetector with high IQE and fast response in a simple silicon technology-compatible device structure.