The direct bandgap of gray α -tin investigated by infrared ellipsometry

Rigo A. Carrasco, Cesy M. Zamarripa, Stefan Zollner, Jose Menendez, Stephanie A. Chastang, Jinsong Duan, Gordon J. Grzybowski, Bruce B. Claflin, Arnold M. Kiefer

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13 Scopus citations


Using Fourier-transform infrared ellipsometry, the authors provide spectroscopic evidence about the valence band (VB) structure of diamond-like α-tin. The mid-infrared dielectric function of α-tin grown pseudomorphically on InSb or CdTe by molecular beam epitaxy shows a strong Ē0 peak near 0.41 eV. This peak is assigned to allowed intravalence band transitions from the Γ7- (electron-like) VB to the Γ8+v heavy hole VB and/or interband transitions from Γ7- to the Γ8+c light "hole" conduction band. The strength of this peak requires a hole density in the mid-1018 cm-3 range at room temperature, which might be caused by unintentional doping, by thermal electron-hole pair generation, or by the possibility that the L6+ conduction band might have an energy slightly lower than the Γ8+ VB maximum. Alternatively, this Ē0 peak might be enhanced by the M-shape of the Γ7- VB caused by interactions with the Γ7+ split-off hole VB. A sum-rule analysis of the dielectric function between 0.16 and 6.5 eV is consistent with a high-frequency dielectric constant of 24, which has at most a weak temperature dependence between 100 and 300 K.

Original languageEnglish (US)
Article number232104
JournalApplied Physics Letters
Issue number23
StatePublished - Dec 3 2018

ASJC Scopus subject areas

  • Physics and Astronomy (miscellaneous)


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