Unique Detection Properties of Vertical Ge Avalanche Detectors With Ge Nanopillar Array

The photodetector in the near-infrared band is playing an increasingly important role in various industries such as optical communication, environmental detection, and biomedical imaging. In this article, we report on an <inline-formula> <tex-math notation="LaTeX">$8\times 8$ </tex-math></inline-formula> array of all germanium (Ge)-based vertical p-n photodetectors enhanced by Ge nanopillars. These nanopillars can significantly improve the light absorption efficiency in a broad spectral range and suppress the dark current; therefore, the broadband enhancement of responsivity and specific detectivity from 550 to 1800 nm is observed in the device. In particular, the maximum enhancement factor of responsivity and specific detectivity at 1550 nm is over 112.59% and 279.9%, respectively, under the −1-V bias voltage. When avalanche breakdown is reached under a bias over −9 V, the ultraresponsivity (161.67 A/W) and gain (53.83) are also obtained in the device with nanopillars. These results indicate that the detection ability of Ge avalanche detectors can be efficiently improved by photon-trapping nanostructures, which helps for the rapid development of group IV photodetectors.