It has been demonstrated that two closely spaced peaks in the infrared absorption spectra of several HgTe/ Hg 1−x Cd x Te͑112͒B superlattices ͑SL's͒ are due to the H1-E1 intersubband transition at the center of the Brillouin zone and the zone boundary. The miniband width agrees well with ͑8 ϫ 8 k · p͒ calculations. The intersubband transition energies of SL's with both large and small miniband widths have been compared with photoluminescence ͑PL͒ spectra over a temperature range of 5 -300 K for a number of superlattices with band gaps between 100 and 510 meV at 5 K. The band gap as determined from the peak of the first derivative of the absorption coefficient, i.e., the corresponding intersubband transition energy, agrees well with the PL peak energy. With increasing temperature the PL peak energy increases faster than the band gap by a range of factors given by 0.25-0.75k B T, however, which are well within the width of the thermally broadened PL peaks.

In this study, high-resolution diffraction has been used to investigate the strain state and uniformity of (001) and (112) oriented HgTe-CdTe superlattices grown by molecular beam epitaxy. A number of reciprocal space maps were taken over the surface of the grown wafer, and variations in the spread of lattice spacings and tilts were quantified and used to identify the presence of local defects. Though all growths were fully strained, those with a larger mismatch exhibited a greater spread of lattice tilts from the substrate to the superlattice layers in both orientations. Further, the variation in composition of the CdZnTe substrates resulted in a variation of strain over the surface of the superlattice, and evidence of areas of significant dislocation densities present in substrate layer corresponded with defect-rich areas in the superlattice layer.

Results of photoresponse measurements performed on long-wave infrared photoconductors fabricated from HgTe-HgCdTe superlattices grown by molecular beam epitaxy are presented. Absolute spectral photoresponse measurements as a function of temperature and applied electric field have be undertaken, with the peak photoresponse of 3.3×103 V/W measured at 100 K. Sweepout effects were observed for fields greater than 20 V/cm and quantum efficiencies approaching 80% for 5 μm thick devices have been predicted from absorption measurements of grown material.

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