Der Einfluß der freien Ladungsträger auf die optischen Konstanten des Bi2Se3 im Wellenlängengebiet von 2 bis 23 μm

The influence of free carriers on the optical constants of Bismuthtriselenide Bi₂Se₃ was investigated in the infrared (2–23 μm). The reflection and transmission ofn-type Bi₂Se₃ single crystals was measured at approximately 30, 80 and 300 °K. Up till now,p-type Bi₂Se₃ is not known. The dependence of the refraction index and the absorption constant on the wavelength was calculated from the results of the measurements. It was found that the optical constants strongly depend on the carrier concentration. The crystals were prepared according the bridgman method. They normally have a carrier concentration of about 10¹⁹ cm^?3, which can be diminished by annealing in Selenium vapour of various pressure up to 10¹⁸ cm^?3. Bismuthtriselenide is a degenerated semiconductor. We obtained for the optical energy band gap by extrapolation the value 0,21 eV. It increases with increasing carrier concentration. This is known as the Burstein-Moss-effect.