Abstract
The infrared reflectivity was measured as a function of hole concentration at 82 °K for alloy samples with and as a function of temperature for one sample with and hole concentration 8.7× . The measured reflectivity spectra were remarkably well fitted by the classical free-carrier dispersion relations. The optical dielectric constant , the susceptibility effective mass , and the optical mobility were determined from a curve-fitting technique and a minimum-reflectivity technique generalized to include the effect of nondegeneracy. Using the former technique, a second valence-band maximum situated at about 0.23 eV below the main valence-band maximum was detected in the alloy with . The energy gap and were found to be related by in lead-rich alloys. The optical mobility was found to be about a factor of 2 lower than the conductivity mobility in all samples measured. The experimental values of were compared with those expected from the Kane, Cohen, and Dimmock models. The results of these comparisons indicate that the two-band models of Kane and Cohen, especially the former, are more suitable than the six-band model of Dimmock to explain the carrier-concentration dependence of , and that none of the models account for the large increase of with temperature.
- Received 25 April 1972
DOI:https://doi.org/10.1103/PhysRevB.6.3898
©1972 American Physical Society