Electrical and Optical Properties of Amorphous and Monoclinic Selenium under Very High Pressure

The conductivity of amorphous, monoclinic, and trigonal selenium has been measured at 300°K as a function of quasihydrostatic pressure up to 150 kbar. Amorphous and monoclinic samples after exposure to pressure above 120 kbar are transformed irreversibly to the trigonal modification. This result is confirmed by the direct observation of the corresponding shift of the absorption edge. Besides conductivity, for amorphous selenium the shift of absorption edge with pressure is investigated. The resulting pressure coefficient of the band gap is in good accordance with the value obtained from the pressure dependence of the conductivity with the assumption that intrinsic conduction predominates in amorphous selenium.