Near-infra-red sensing with silicon is limited by the bandgap of silicon, corresponding to a maximum wavelength of
absorption of 1.1 μm. A new type of CMOS sensor is presented, which uses a SiGeC epitaxial film in conjunction with
novel device architecture to extend absorption into the infra-red. The SiGeC film composition and thickness determine
the spectrum of absorption; in particular for SiGeC superlattices, the layer ordering to create pseudo direct bandgaps is
the critical parameter. In this new device architecture, the p-type SiGeC film is grown on an active region surrounded by
STI, linked to the S/D region of an adjacent NMOS, under the STI by a floating N-Well. On a n-type active, a P-I-N
device is formed, and on a p-type active, a P-I-P device is formed, each sensing different regions of the spectrum. The
SiGeC films can be biased for avalanche operation, as the required vertical electric field is confined to the region near
the heterojunction interface, thereby not affecting the gate oxide of the adjacent NMOS. With suitable heterojunction
and doping profiles, the avalanche region can also be bandgap engineered, allowing for avalanche breakdown voltages
that are compatible with CMOS devices.
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