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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.

In two recent review papers on metal organic vapour phase epitaxy (MOVPE) of cadmium mercury telluride (CMT) particular emphasis was placed on the crucial importance of doping studies to the realization of future device structures. If the full potential of MOVPE growth of CMT is to be realized then extrinsic doping of heterostructures is required. If the doping and composition junctions can be grown wiin tine correci degree of grading then inis wili creaie ihe poteniiai ior ?ne production of device structures leading to either improved performance and/or increased operating temperatures. This paper will review published doping studies and also present some recent results on both acceptor and donor doping studies carried out by the authors. In the latter studies, interdiffused multilayer process (IMP) growth of CMT has been performed at 0360 "C using dimethyl cadmium (DMC) and di-isopropyl tellurium (DIPT) as the MO precursors while t h e Hg overpressure was provided by a heated elemental source. Alternative acceptor doping sources to arsine have been investigated including phosphine, triphenyl arsenic, and phenyl arsenic of which the latter appears to be most suitable. Iodine has continued to show the donor dopant potential in CMT that it exhibited with higher-temperature (0400 "C) MOVPE growth using di-ethyl tellurium (ET). Characterization o i iuiiy doped structures wiii be described.

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