Backside Illuminated “Ge-on-Si” NIR Camera

In this paper, a near-infrared “Ge-on-Si” camera with backside illumination, is presented. The camera consists of a photonic chip, a readout chip, and a commercial microcontroller, which is connected to a laptop via USB. The functionality of two-dimensional ( 10×10 pixels) as well as one-dimensional ( 64×1 pixel) “Ge-on-Si” pixel arrays with a pitch of 25 μm are demonstrated. The photonic chip consists of basic CMOS technology process in combination with a molecular beam epitaxy growth process. With this technology and the backside illumination a high fill-factor of 74% is achieved. Further the “Ge-on-Si” detectors are operated under zero bias operation in order to minimize the dark current and thus to maximize the signal-to-noise ratio. This enables dark currents better than 100 pA to be achieved in each pixel. A linear behavior between photocurrent and optical power of the “Ge-on-Si” detectors over a large dynamic range for optical powers between 10 ^-7 W and 10 ^-2 W is shown. With relatively thin Ge absorption layers of only 400 nm, optical responsivities of 0.36 A/W at a wavelength of 1310 nm could be achieved. The functionality of the “Ge-on-Si” camera is demonstrated by the movement of a single mode fiber over the photonic chip at a wavelength of 1310 nm.