Applicability of the empirical Varshni relation for the temperature dependence of the width of the band gap
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We have carried out a comparison of relations used to describe the temperature dependence of the width of the band gap in crystals. It is shown that for kT≫ℏω the well-known Varshni relation can be obtained from the non-empirical Fan expression in explicit form taking account of the phonon statistics. We have calculated the temperature coefficient bof the width of the band gap for a number of materials in the range where the high-temperature condition is not met. We have found that the Varshni relation overestimates β, whereas calculations based on the Fan expression agree with experiment.
KeywordsSpectroscopy State Physics Explicit Form Temperature Coefficient Phonon Statistic
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