Bulk Defect-Mediated Absorption Sub-Bandgap All-Silicon Photodetector with Low Dark Current Density at Ambient Temperatures

In this work, we made a bulk defect-mediated absorption (BDA) sub-bandgap all-Si photodetector (PD) with low dark current density and high detectivity at ambient temperatures (223–293 K). The testing wavelength is chosen as 1319 nm. Pt layer was deposited onto the surface of black Si, followed by annealing at 950 °C, to form a bulk defect energy band for sub-bandgap near-infrared (NIR) absorption. The Al2O3 layer was applied to the front side of the PD as a typical passivating layer to passivate the surface of the black Si. The ZnO layer was applied to the rear side of the PD to block the dark current arising from the introduced bulk defect band. The synergetic introduction of the passivating and blocking layers reduced the dark current significantly by 2 to 3 orders of magnitude. For the PD after thickness optimization of passivating and blocking layers in this work, at 293 and 223 K, the dark current densities finally achieved were 6.0 × 10–8 and 1.6 × 10–9 A/cm2, with responsivities of 3.9 and 2.9 mA/W and specific detectivities of 2.8 × 1010 and 1.2 × 1011 cm·(Hz)1/2/W, respectively, at a bias of 0.3 V. The all-Si NIR PD developed here would have promising applications in cost-effective, low-light-level, NIR detection and imaging.