Designer Ge Quantum-Dot Phototransistors for highly-integrated, broadband optical interconnects

Abstract

We report high-responsivity Ge quantum dots (QDs) MOS phototransistors as on-chip transducers for highly-integrated, broadband Si-based optical interconnects. Self-organized heterostructure of Ge-QD/SiO2/Si-channel is fabricated in a single step through selective oxidation of SiGe nano-pillars over a Si3N4 buffer layer on Si substrates. Dark current densities (10(-7)A/mm(2)), photocurrent-to-dark current ratio (similar to 10(7)) and photoresponsivities (>10 A/W), external quantum efficiency (similar to 240%), and response time (1.4ns) are measured on the Ge-QD phototransistors under 850 nm illumination. Detection wavelength is tunable from near infrared to near ultraviolet by reducing the QD size from 90 to 7 nm, and the optimal photoresponsivity is tailored by the QD size and effective thickness of gate dielectrics.