Zero biased Ge-on-Si photodetector on a thin buffer with a bandwidth of 3.2Â GHz at 1300Â nm

A Ge-on-Si photodetector grown on a thin buffer on top of a Si substrate is presented. The device exhibits a zero bias bandwidth of 3.2 GHz and a photoresponsivity of 104 mA/W for a wavelength of 1300 nm. Zero bias operation is proposed to minimize the influence of dark currents on the device performance. The photoresponsivity for wavelengths near the absorption edge of Ge exceeds the values expected from absorption data of unstrained Ge reported in the literature. The depletion characteristics of the device are extracted from S-parameter-measurements using a small-signal equivalent circuit. The bandwidth of the device is limited by the RC-time constant and can be further increased, if the defect density is reduced.