Optical Properties of Tellurium in the Fundamental Absorption Region

Abstract

An analysis has been made of the optical absorption edge and reflectivity spectrum of single-crystal tellurium. Transmission measurements, using polarized light, were made between 10 and 300°K covering a range of absorption coefficient from 0.4 ${\mathrm{cm}}^{-1\mathrm{}}$ to 5×${10}^3$ ${\mathrm{cm}}^{-1\mathrm{}}$. Below 100°K a sign reversal of the temperature coefficient of the absorption edge was observed for both directions of polarization. The lowabsorption region for $\mathbf{E}\parallel c$ showed behavior indicative of indirect transitions, while the absorption edge for $\mathbf{E}\perp c$ varied exponentially with photon energy for over two decades. These features, together with the observation of an exciton at 0.336 eV for $\mathbf{E}\perp c$, are similar in nature to those previously reported for trigonal selenium. Optical constants, such as the real and imaginary parts of the dielectric constant, have been calculated over a wide range of wavelengths at 10°K, as well as at 300°K, by applying the Kramers-Kronig relation to the reflectivity spectrum.