TUNABLE, LONG-WAVELENGTH PTSI SIGE/SI SCHOTTKY DIODE INFRARED DETECTORS/

We have fabricated p-type PtSi/SiGe/Si Schottky diodes with barrier he ights (from photoresponse) that are lowered (relative to PtSi/Si) and highly dependent on the applied bias. The variability in the barrier h eight is obtained by using the SiGe/Si valence band offset as an addit ional barrier. When placed in close proximity to the PtSi/SiGe Schottk y barrier, the total effective barrier can be altered dramatically by adjusting the applied reverse bias. The voltage sensitivity of the tot al barrier height can be controlled by the SiGe layer thickness. The v oltage-variable barrier heights range, for example, from 0.30 eV at ze ro bias to 0.12 eV at 2.4 V reverse bias for a 20%, 450 Angstrom thick -SiGe layer. This lowest barrier height corresponds to a cutoff wavele ngth of 10 mu m, extending the detection range of PtSi infrared detect ors to the long-wavelength range. The quantum efficiency coefficients C-1 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 loss es from quasielastic scattering in the SiGe are taken into account in a theoretical model that gives good agreement with data. (C) 1995 Amer ican Institute of Physics.