Ge and Si Microcrystal Photodetectors with Enhanced Infrared Responsivity*

Ge and Si micro-crystals, grown on Si patterned substrates, can be used as absorbing elements for photodetection in the near-infrared. In such microstructures, light confinement effects due to crystal facet, enhance light absorption in the near-infrared as compared to conventional epitaxial layers. Devices based on single micro-crystals and on micro-crystals arrays have been fabricated and characterized. The photocurrent of Si photodetectors based on single micro-crystals have been measured in linear and avalanche regime, demonstrating a state-of-the-gain of $\approx 10^{4}$. Ge-on-Si photodetectors based on micro-crystal arrays, fabricated using graphene as top contact, have also been fabricated, showing a responsivity in the 1500-1800 nm exceeding that of conventional planar devices.