Pseudomorphic p-GexSi1-x/Si quantum-well infrared photodetectors for normal incidence operation between 20K and 77K

Normal incidence spectral response and bias dependent responsivity measurements on p-type Ge x Si 1-x /Si quantum well infrared photodetectors reveal anomalous long wavelength photoresponse, extending out to 18 micrometers depending on quantum well parameters. Room temperature FTIR absorptance measurements do not reveal significant absorption in this wavelength range; aside from the shorter wavelength intersubband optical transitions near 6 - 12 micrometers in these Ge 0.25 Si 0.75 quantum wells. Dark current induced filling of the higher-lying split-off hole state, with subsequent optical absorption, would give rise to infrared absorption in the 14 - 18 micrometers range; however the split-off ground state to heavy-hole ground state lifetime required is -10 microsecond(s) ecs. In two-hole state structures having 300 angstroms barriers we observe dramatic increases in responsivity for bias voltage above 3 V, attributed to hot-hole transport enhancement of the photoconductive gain. This behavior is not observed in 500 angstroms barrier width structures.