Regensburg 2019 – wissenschaftliches Programm

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DS: Fachverband Dünne Schichten

DS 1: Optical Analysis of Thin Films I (Reflection, Ellipsometry, Raman, IR-DUV Spectroscopy, ...

DS 1.4: Vortrag

Montag, 1. April 2019, 10:45–11:00, H32

Direct band gap of alpha-tin investigated by infrared ellipsometry — Rigo A. Carrasco¹, Cesy M. Zamarripa¹, •Stefan Zollner¹, and Jose Menendez² — ¹New Mexico State University, Las Cruces, NM — ²Arizona State University, Tempe, AZ

Interest in gray tin has been revived because it is the endpoint constituent of Ge_1−xSn_x alloys, which have potential applications as mid-infrared detectors and lasers. α-tin also becomes a topological insulator or Dirac semimetal under stress. The band structure for gray tin is similar to Ge, but the Γ₇⁻ s-antibonding band, which is the conduction band in Ge, moves downward in gray tin and appears between Γ₈⁺ and Γ₇⁺ with a negative energy Ē₀ if we conventionally choose Γ₈⁺ as the zero energy level.

Using Fourier-transform infrared ellipsometry, we provide spectroscopic evidence about the valence band structure of 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. The peak can be attributed to allowed intra-valence band transitions from the Γ₇⁻ (electron-like) to the Γ₈^+v heavy hole valence band and/or interband transitions from the Γ₇⁻ band to the Γ₈^+c light "hole" conduction band. Possible sources for the strength of the peak, and its temperature dependence will be discussed. We would like to thank Dr. Arnold M. Kiefer and Stephanie Chastang for providing us the strained α-tin samples.