Scanning tunneling optical spectroscopy in mercury cadmium telluride and related compounds

We consider II-VI narrow gap semiconducting alloys. mercury cadmium telluri de, Hg(1-x)Cd(x)Te (MCT), mercury zinc telluride, Hg(1-x)Zn(x)Te (MZT), and mercury zinc selenide, Hg(1-x)Zn(x)Se (MZS). MCT is emphasized for actual calculations, but a table of values needed in all calculations is presented . These materials are of interest because of their application to infrared detectors and related devices, and because they are candidates for low grav ity crystal growth to improve uniformity. We present new calculations of th e scanning tunneling optical spectroscopy (STOS) current from which the loc al energy gap, a function of x, and hence the stoichiometry (x) can be dete rmined as a function of position with presumably high spatial resolution. T he low temperature tunneling current (vs. photon frequency) has a sharper o nset at the band gap than the low temperature optical absorption. This shar p onset originates from the rapid increase in the integrated transmission p robabilities and is greatly enhanced by large diffusion lengths. Thus, STOS should be a competitive technique, compared to optical absorption, for det ermining the local stoichiometry, a property that is important for characte rizing crystals. (C) 1999 Published by Elsevier Science B.V. All rights res erved.