Ge-based mid-infrared blocked-impurity-band photodetectors

Mid-infrared blocked-impurity-band (BIB) photonic detectors are developed by sulfur (S) ions implantation into germanium (Ge) crystal. The detectors demonstrate wide photoresponse spectra ranging from 2 to 10 μm with peak response at about 6 μm. We characterize photocurrent spectra of two operating modes, forward bias mode (FBM) and reverse bias mode (RBM), and find that RBM has a lower optimum bias but a bigger photocurrent. Effect of different blocking layer (BL) length on photocurrents for the two operating modes is studied. When BL length increases, the ratio of the relative photocurrent under RBM to that under FBM at respective optimum bias enlarges. The slope of the electric field profile in BL leads to the differences of optimum bias and maximum photocurrent between two modes. The electric field strength in AL under RBM strengthens as BL length increases, resulting in larger photocurrent for longer BL.