Effects of sulfur isotopic composition on the band gap of PbS
2006; American Physical Society; Volume: 73; Issue: 23 Linguagem: Inglês
10.1103/physrevb.73.233202
ISSN1550-235X
AutoresHuihui Lian, A. Yang, M. L. W. Thewalt, R. Lauck, M. Cardona,
Tópico(s)Advanced Thermoelectric Materials and Devices
ResumoLow temperature photoluminescence spectra of synthetic $\mathrm{PbS}$ crystals having the natural isotopic abundance (95% $^{32}S$) are compared with crystals grown using 99% $^{34}S$. An anomalous decrease in the band gap energy of $6.5\ifmmode\pm\else\textpm\fi{}2\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ with increasing $S$ mass was observed. The unusual sign of this isotope shift can be related to the temperature dependence of the band gap energy, which opposite to the behavior seen for most common semiconductors, increases strongly between $2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and $320\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. This temperature dependence was measured with improved accuracy using absorption spectroscopy, and a fit to this data suggests that there should be virtually no net renormalization of the band gap energy due to zero point motion at low temperatures. This must result from a cancellation of the contributions from $S$ and Pb, but the predicted ``normal'' isotope shift of the band gap energy with Pb mass is too small to be measured.
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