High-efficiency metal-semiconductor-metal photodetectors on heteroepitaxially grown Ge on Si

We demonstrate extremely efficient germanium-on-silicon metal–semiconductor–metal photodetectors with responsivities $\left(\mathfrak{R}\right)$ as high as $0.85\mathrm{A}∕\mathrm{W}$ at $1.55\mathrm{\mu }\mathrm{m}$ and $2\mathrm{V}$ reverse bias. Ge was directly grown on Si by using a novel heteroepitaxial growth technique, which uses multisteps of growth and hydrogen annealing to reduce surface roughness and threading dislocations that form due to the 4.2% lattice mismatch. Photodiodes on such layers exhibit reverse dark currents of $100\mathrm{mA}∕{\mathrm{cm}}^2$ and external quantum efficiency up to 68%. This technology is promising to realize monolithically integrated optoelectronics.