Metal-germanium-metal photodetectors on heteroepitaxial Ge-on-Si with amorphous Ge Schottky barrier enhancement layers

We report a metal-Ge-metal photodetector fabricated on a Ge epitaxial layer grown on Si (100) substrate. Amorphous Ge was used to increase the Schottky barrier height, which resulted in a reduction of the dark current by more than two orders of magnitude. The dark current measured on a photodetector having 1 μm finger width and 2 μm spacing with 25×50 μm² active area was 7.5 μA at 3 V. At the wavelength of 1.3 μm, the external quantum efficiency was 14.3% (0.15 A/W) without an antireflecting coating. At reverse biases of 1, 2, 3, and 4 V, the 3-dB bandwidth was found to be 1.5, 2.8, 3.1, and 4.3 GHz, respectively.