TABLE OF CONTENTS The cutoff of InSb is ~5.5 ?m at 77K and ~7 ?m at 300K. Many applications require longer wavelength detection. Because 300K radiation has a peak around 9 to 11 ?m, IR detectors that detect in this region are useful for thermal imaging applications. Thus, there is a great amount of work in IR detector material covering the 8- to 12 ?m wavelength region.
Among III-V semiconductor alloys, InAsSb has the lowest bandgap (with the exception of Tl- and Bi- containing alloys). Experimental results have showed that InAsSb can cover the entire 8- to 12- ?m range at near ambient temperature (200 300K). It is a promising material system for uncooled photon detectors for LWIR applications.
The InAs 1- xSb x alloy has a zinc-blende structure and direct gap at the Brillouin zone center. The shape of the electron band and the light hole band is determined by k p theory. According to Wieder and Clawson [49], the energy gap of In As 1- xSb x may be described by the following expression:
| (7.8) |  |
Some recent studies show that the minimum bandgap can be considerably less compared to that predicted by (7.8). Bethea et al. [50] estimated the 300K bandgap of InAs 0.22Sb 0.78 to be 0.095eV. They also measured significant photoconductivity at 10 ?m at 77K. Chiang and Bedair [51] reported an ~9- ?m cutoff wavelength of x =
