High operating temperature (HOT) detector concepts using midwave infrared (MWIR) (x ϳ 0.3) p-type HgCdTe operating at temperatures within the thermoelectric cooler range are of significant interest at the present time. However, it is apparent that much work remains to be done in the areas of material, diode passivation, and diode formation technologies before the "holy grail" of photon detection at room temperature for all infrared wavelengths is achieved. Over the years, at DRS, we have developed a technology base for both n-and p-type HgCdTe materials parameters that are relevant to photodiode design and fabrication. This paper will discuss data that we have taken recently on minority carrier lifetime in MWIR and long wave infrared (LWIR) HgCdTe, particularly p type, and how it compares to current theories of Auger 7, radiative, and Shockley-Read recombination in this material. Extrinsic group IB (Cu, Au) and group V (arsenic) p-type dopants were used, together with group III (In) for n-type. The impact of the data on future HOT detector work is discussed.

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Using a quasichemical approach, the total native defect concentration and the minimum deviation in stoichiometry have been calculated in CdTe crystals as a function of the Cd pressure at various temperatures. With this knowledge, CdTe and (Cd,Zn)Te wafers have been subjected to postgrowth step annealing treatment under conditions such that the crystals are in equilibrium with a Cd or (Cd,Zn) vapor corresponding to the minimum in deviation from stoichiometry at each annealing temperature. The step annealed CdTe and (Cd,Zn)Te wafers have been examined under infrared microscopy and have shown significant reduction in the concentration of Te precipitates, whereas the unannealed wafers have had numerous Te precipitates distributed throughout the bulk. HgCdTe epitaxial films have been grown on the step annealed CdTe and (Cd,Zn)Te wafers as well as on unannealed wafers from the same boule. Examination of the cross sections of the epitaxial films indicates appearance of Te precipitates in films grown on unannealed substrates, whereas no Te precipitation was evident in films grown on the annealed substrates leading to the inference that the occurrence of Te precipitates in the (Hg,Cd)Te films is possibly related to the presence of Te precipitates in the substrates. Thermal migration of Te under a temperature gradient during step annealing is suggested as a possible mechanism in the elimination of larger size Te precipitates whereas the extremely fine precipitates (<1 μm) appear to need in-diffusion of metal vapor for their elimination.

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Carrier recombination lifetime measurements and analyses based on Shockley-Read-Hall, radiative, and Auger recombination mechanisms were utilized to characterize the material quality of HgCdTe grown by molecular beam epitaxy. The Auger recombination mechanism employed in this analysis is in the theoretical framework according to Beattie and Landsberg ͓Proc. R. Soc. London, Ser. A 249, 16 ͑1959͔͒, which we independently re-evaluated using the electronic band structures computed with a 14-band k · p methodology and direct evaluations of the transition rates. The Levenberg-Marquette method was used to fit the temperature-dependent carrier recombination lifetimes as measured by the photoconductive decay technique. Based on the above methods, carrier recombination lifetime measurements were developed as a routine characterization technique.