Absorption and Electroabsorption of Trigonal Selenium near the Fundamental Absorption Edge

Abstract

The absorption spectrum and the spectrum of electroabsorption of vapor-grown trigonal Se platelets have been measured at various temperatures down to 2°K. The absorption curves for both $\overrightarrow{\mathrm{E}}\parallel c$ and $\overrightarrow{\mathrm{E}}\perp c$ show several steps at the onset of the absorption edge. No Urbach tail has been found. The steps are interpreted as arising from the indirect excitation of an exciton at 1. 853 eV (low-temperature value) with several phonons. The electroabsorption spectra confirm the step structure within the absorption edge. Finally, it is shown that the luminescence of Se can also be explained with the same model.