Interband absorption edge in topological insulators Bi${}_2$(Te${}_{1-x}$Se${}_x$)${}_3$

Abstract

We have investigated the optical properties of thin films of topological insulators Bi${}_2$Te${}_3$, Bi${}_2$Se${}_3$ and their alloys Bi${}_2$(Te${}_{1-x}$Se${}_x$)${}_3$ on BaF${}_2$ substrates by a combination of infrared ellipsometry and reflectivity in the energy range from 0.06 to 6.5 eV. For the onset of interband absorption in Bi${}_2$Se${}_3$, after the correction for the Burstein-Moss effect, we find the value of direct bandgap of $215\pm 10$ meV at 10 K. Our data supports the picture that Bi${}_2$Se${}_3$ has a direct band gap located at the $\Gamma$ point in the Brillouin zone and that the valence band reaches up to the Dirac point and has the shape of a downward oriented paraboloid, i.e. without a camel-back structure. In Bi${}_2$Te${}_3$, the onset of strong direct interband absorption at 10 K is at a similar energy of about 200 meV, with a weaker additional feature at about 170 meV. Our data support the recent GW band structure calculations suggesting that the direct interband transition does not occur at the $\Gamma$ point but near the Z-F line of the Brillouin zone. In the Bi${}_2$(Te${}_{1-x}$Se${}_x$)${}_3$ alloy, the energy of the onset of direct interband transitions exhibits a maximum near $x=0.3$ (i.e. the composition of Bi${}_2$Te${}_2$Se), suggesting that the crossover of the direct interband transitions between the two points in the Brillouin zone occurs close to this composition.

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Cited by in corpus (8)

• Infrared dielectric metamaterials from high refractive index chalcogenides
• Revealing Optical Transitions and Carrier Recombination Dynamics within the Bulk Band Structure of Bi2Se3
• Landau level spectroscopy of Bi${}_2$Te${}_3$
• Van Hove Singularity Arising from Mexican-Hat-Shaped Inverted Bands in the Topological Insulator Sn-doped Bi${}_{1.1}$Sb${}_{0.9}$Te${}_2$S
• Electronic band structure of Sb2Te3
• Designer topological insulator with enhanced gap and suppressed bulk conduction in Bi2Se3/Sb2Te3 ultra-short period superlattices
• Observation of optical absorption correlated with surface state of topological insulator
• Anisotropy in the dielectric function of Bi${}_2$Te${}_3$ from first principles: From the UV-visible to the infrared range