Tunable, long-wavelength PtSi/SiGe/Si Schottky diode infrared detectors

We have fabricated p-type PtSi/SiGe/Si Schottky diodes with barrier heights (from photoresponse) that are lowered (relative to PtSi/Si) and highly dependent on the applied bias. The variability in the barrier height is obtained by using the SiGe/Si valence band offset as an additional barrier. When placed in close proximity to the PtSi/SiGe Schottky barrier, the total effective barrier can be altered dramatically by adjusting the applied reverse bias. The voltage sensitivity of the total barrier height can be controlled by the SiGe layer thickness. The voltage-variable barrier heights range, for example, from 0.30 eV at zero bias to 0.12 eV at 2.4 V reverse bias for a 20%, 450 Å thick SiGe layer. This lowest barrier height corresponds to a cutoff wavelength of 10 μm, extending the detection range of PtSi infrared detectors to the long-wavelength range. The quantum efficiency coefficients C₁ are normal at this long-wavelength end, but reduced over the rest of the tunable range, because hot carriers have to traverse the entire SiGe thickness in order to be detected. The hot carriers' energy losses from quasielastic scattering in the SiGe are taken into account in a theoretical model that gives good agreement with data.