Photoconductivity and Photoacoustie Spectra of Trigonal, Rhombohedral, Orthorhombic, and α-, β-, and γ-Monoclinic Selenium

Photoconductivity and photoacoustic spectra of all known crystalline allotropes of selenium have been measured. Both the photocurrent peaks and the absorption edges have a tendency to shift monotonously to lower energy region with the increase in density, even though the constituents of the crystals are different, suggesting that the band gap decreases with the increase in intermolecular interaction.