High detectivity Ge photodetector at 940 nm achieved by growing strained-Ge with a top Si stressor

We have developed a self-powered near-infrared photodetector (PD) with high detectivity using a tensile strained Ge layer capped with a thick Si layer. The Si layer acts as a stressor and maintains the strain of Ge with minimal dislocations by creating a rough surface. By using Raman spectroscopy, we confirmed that the Ge layer has a 1.83% in-plane tensile strain. The Ge PD exhibits a high responsivity of 0.45 A/W at -1 V bias voltage for 940 nm wavelength. The PD's dark current density is as low as ∼1.50 × 10^-6 A/cm² at -1 V. The high responsivity and low dark current result in a detectivity as high as 6.55 × 10¹¹ cmHz^1/2/W. This Ge PD has great potential for applications in light detection and ranging (LiDAR), Internet of Things (IoTs), and Optical Sensing Networks.