The split-geometry design for arrays of photoconductive HgCdTe infrared photodetectors described in the preceding article can also be used to mitigate the deleterious effect of a phenomenon called "sweepout," which degrades performance. Sweepout occurs in conventional small HgCdTe photodetectors operated at high bias voltages; it causes undesired recombination of minority charge carriers at metal/semiconductor interfaces.
The split-geometry design improves performance by delaying the onset of sweepout to higher bias levels. It increases current-path lengths and thereby increases the electrical resistances of detectors. The split-geometry design is being used in the development of improved long-wave-sounder (LWS) detectors for the Geostationary Operational Environmental Satellite (GOES), and is expected to be used in the development of GOES imaging devices.
When detectors of split-geometry design are operated under optimal bias conditions, they exhibit responsivities and detectivities higher, and power dissipations and 1/f-noise knees lower, than those of conventional LWS photodetectors. By combining the split-geometry design with operation at relatively low bias, one can minimize the deleterious effect of sweepout. HgCdTe devices designed and operated following this approach have exhibited detectivities as high as 6 ×1010cm Hz 1/2 /W at a temperature of 80 K and a cutoff wavelength of 17.2 µm.
This work was done by Bob Martineau, Andre Burgess, Sridhar Manthripragada, Frank Peters, Brent Mott, and Peter Shu of Goddard Space Flight Centerand Kelley Hu and Jack Shi of HSTX. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com under the Electronic Components and Systems category. GSC-13810