HIGH-QUALITY GERMANIUM PHOTODIODES INTEGRATED ON SILICON SUBSTRATES USING OPTIMIZED RELAXED GRADED BUFFERS

The integration of Ge photodetectors on silicon substrates is advantag eous for various Si-based optoelectronics applications. We have fabric ated integrated Ge photodiodes on a graded optimized relaxed SiGe buff er on Si. The dark current in the Ge mesa diodes, J(s)=0.15 mA/cm(2), is close to the theoretical reverse saturation current and is a record low for Ge diodes integrated on Si substrates. Capacitance measuremen ts indicate that the detectors are capable of operating at high freque ncies (2.35 GHz). The photodiodes exhibit an external quantum efficien cy of eta=12.6% at lambda=1.3 mu m laser excitation in the photodiodes . The improvement in Ge materials quality and photodiode performance i s derived from an optimized relaxed buffer process that includes a che mical mechanical polishing step within the dislocated epitaxial struct ure. (C) 1998 American Institute of Physics. [S0003-6951(98)00241-1].