Enhancing the sub-bandgap photo-response of silicon by inert element co-hyperdoping

The introduction of intermediate bands by hyperdoping is an efficient way to realize infrared light absorption of silicon. In this Letter, inert element (helium and argon for specific)-doped black silicon is obtained by helium ion-implantation followed by femtosecond pulse laser irradiation in an argon atmosphere based on near-intrinsic silicon substrates. Within the 200 nm of the silicon surface, the concentrations of helium and argon are both above the order of 10¹⁹ cm^-3. The defect states related to impurities and structural defects contribute to the absorption in sub-bandgap (1100-2500 nm). Vertically structured devices based on the inert element-doped black silicon exhibit the responsivity of 350 mA/W for 1550 nm and 165 mA/W for 1310 nm at 12 V operating bias, respectively, proving its potential application in infrared detection.