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 ellipsometryRigo A. Carrasco1, Cesy M. Zamarripa1, •Stefan Zollner1, and Jose Menendez21New 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 Ge1−xSnx 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.

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