Photoresponse Enhancement in Ge MSM Photodetector With Ge Micropillar Array

Improving detection efficiency of Ge photodetector near the absorptance edge is crucial for fiber-optic telecommunication. Here, we report the unique photodetection properties of germanium (Ge) metal-semiconductor-metal (MSM) photodetector with Ge micropillar array. The responsivity and detectivity of the device at 1550 and 1990 nm are studied. When compared with the Ge photodetector without micropillar, the responsivity and detectivity of micropillar Ge device are improved by 2.76 and 4.21 times at 1550 nm, respectively. This phenomenon is mainly associated with the enhanced absorption efficiency by geometrical light trapping effect and guided modes supported in the micropillar array. Particularly, the values of responsivity and detectivity in the device with Ge micropillar array are enhanced over 29.9 and 37.1 times at 1990 nm than the results in the device without micropillar, which are quite larger than the values at 1550 nm. This feature is related to that the suitable position of absorption enhancement caused by the micropillar array, which can result in the efficiently separation and suppressed recombination of photogenerated carriers under bias voltage. This work provides a feasible approach to broaden the detection wavelength of Ge-based photodetectors, enhance the absorption near the absorption edge, and improve the detection performance.