Optical Properties of MCT

Photoluminescence in Mercury Cadmium Telluride – a Historical Perspective. Part I: 1966-1996

“…The same year (1990) Tomm et al [35] published the first and the only one, to the best of our knowledge, detailed dedicated review on PL in MCT (a number of other materials, including HgMnTe and lead chalcogenides was also considered; some works on PL in MCT were also, as mentioned previously, briefly reviewed later in [5]). Tomm et al concluded, once again, that for narrow-gap MCT the luminescence was dominated by direct interband transitions.…”

“…Obviously, the samples studied by different authors were grown by different methods, had different thermal histories (and, correspondingly, differed in conductivity type and/or carrier concentration), and were given different treatments before measurement. This could result in very different results obtained for nominally very similar samples, at least in application to electrical properties [8,69]; in optical studies, in addition to that, the presence of oxides and residues on the surface can be quite misleading [5,37,68]. Also, as mentioned above, there is also the uncertainty in determining the exact energy gap of MCT (see, e.g., [45,64,70,71]); this uncertainty is of the order of a few meV, which is larger than the exciton binding energy in MCT.…”

“…As narrow-gap MCT has a small electron effective mass and a high dielectric constant, the exciton binding energy in narrow-gap MCT is very small, so that excitons were believed to be usually dissociated even at very low temperatures. In contrast to the PL spectra of many wide-bandgap materials, which are dominated by sets of exciton-related lines, narrow-gap MCT PL spectra could be very simple in structure [5]. PL studies in MCT have also been hindered by the high rate of non-radiative (mostly Auger) recombination and effect of thermal background radiation.…”

“…It has been over 10 years since the optical properties of MCT, including those revealed as a result of PL spectroscopy measurements, were reviewed, and on that occasion they were reviewed very briefly [5]. In this work, we attempt to present a more comprehensive review of the most prominent studies of PL in MCT.…”

“…Yet another factor is the uncertainty in the broadening of the luminescence lines, partly considered in some of the papers reviewed. As discussed, charge carriers and excitons can experience a randomly varying microscopic potential due to the stochastic distribution of Cd and Hg atoms on the cationic site, so a PL peak could be less or more broadened or shifted depending on the nature of the transition involved as well as the random nature of the MCT alloy at that composition [5]. This effect seems to be more pronounced in MBE-grown MCT as the material fabricated by an inherently non-equilibrium method [12].…”