We have made direct pump-probe measurements of spin lifetimes in long-wavelength narrow-gap semiconductors at wavelengths between 4 and 10 m and from 4 to 300 K. In particular, we measure remarkably long spin lifetimes s ϳ300 ps even at 300 K for epilayers of degenerate n-type InSb. In this material the mobility is approximately constant between 77 and 300 K, and we find that s is approximately constant in this temperature range. In order to determine the dominant spin relaxation mechanism we have investigated the temperature dependence of s in nondegenerate lightly n-type Hg 0.78 Cd 0.22 Te of approximately the same bandgap as InSb and find that s varies from 356 ps at 150 K to 24 ps at 300 K. In this material lattice scattering dominates giving a T Ϫ3/2 dependence for the mobility, and we expect a strong temperature dependence of s . There are two main models that have been invoked for describing spin relaxation in narrow-gap semiconductors: the Elliott-Yafet ͑EY͒ model which gives a T Ϫ7/2 dependence of s in this limit and the D'yakonov-Perel model which gives a T Ϫ3/2 dependence. Our results, both in magnitude and temperature dependence of s , imply that the EY model dominates in these materials.

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Dual waveband infrared detectors can be relatively complicated structures requiring stacking of single waveband detectors. The paper discusses variants of the back-to-back diode structure, which allows the detected waveband to be selected simply by changing the polarity of the bias. Results are presented for two structures: a dual waveband structure for two bands in the mid-infrared region and a dual mid-long waveband structure. The spectra are modeled using a method that takes account of interdiffusion between the layers. Radiative cross-talk is estimated for both of the structures and good agreement is found between the theoretical and measured spectra.

Long-wavelength HgCdTe heterostructures on silicon (100) substrates have been grown using metal-organic vapor phase epitaxy. Test diodes have been fabricated from this material using mesa technology and flip-chip bonding. We have demonstrated excellent resistance-area product characteristics for diodes with a 10.2μm cutoff wavelength. R0A values approaching 103Ωcm2 at 80K have been measured and the resistance-area product maintained above 102Ωcm2 at 1V reverse bias. Variable temperature R0A values correspond to expected generation-recombination loss mechanisms between 60 and 120K. Current-voltage characteristics of two diodes at opposite sides of an array indicate that a very uniform imaging long-wavelength infrared array could be fabricated from this material.

Acceptor doping of many II-VI compound semiconductors has proved problematic and doping of epitaxial mercury cadmium telluride (MCT, Hg 1-x Cd x Te) with arsenic is no exception. High-temperature (>400°C) anneals followed by a lower temperature mercury-rich vacancy-filling anneal are frequently required to activate the dopant. The model frequently used to explain p-type doping with arsenic invokes an amphoteric nature of group V atoms in the II-VI lattice. This requires that group VI substitution with arsenic only occurs under mercury-rich conditions either during growth or the subsequent annealing and involves site switching of the As. However, there are inconsistencies in the amphoteric model and unexplained experimental observations, including arsenic which is 100% active as grown by metalorganic vapor-phase epitaxy (MOVPE). A new model, based on hydrogen passivation of the arsenic, is therefore proposed.