High-quality germanium photodiodes integrated on silicon substrates using optimized relaxed graded buffers

The integration of Ge photodetectors on silicon substrates is advantageous for various Si-based optoelectronics applications. We have fabricated integrated Ge photodiodes on a graded optimized relaxed SiGe buffer on Si. The dark current in the Ge mesa diodes, $J_s\text{=0.15\hspace{0.17em}}{\mathrm{mA/cm}}^{\mathrm{2}},$ is close to the theoretical reverse saturation current and is a record low for Ge diodes integrated on Si substrates. Capacitance measurements indicate that the detectors are capable of operating at high frequencies (2.35 GHz). The photodiodes exhibit an external quantum efficiency of $\text{η=12.6\%}$ at $\text{λ=1.3\hspace{0.17em}μ}\mathrm{m}$ laser excitation in the photodiodes. The improvement in Ge materials quality and photodiode performance is derived from an optimized relaxed buffer process that includes a chemical mechanical polishing step within the dislocated epitaxial structure.