Intrinsic Optical Absorption in Tellurium

Measurements of intrinsic optical absorption have been made at 100 and 300°K by transmission techniques, covering a range of absorption coefficient from 0.01 ${\mathrm{cm}}^{-1\mathrm{}}$ to 1000 ${\mathrm{cm}}^{-1\mathrm{}}$ for radiation polarized E∥C, and to 5000 ${\mathrm{cm}}^{-1\mathrm{}}$ for E ⊥ C. These results suggest that the edge is set by vertical transitions, the transition being allowed for the polarization E ⊥ C but forbidden for E∥C. Absorption above the intrinsic threshold is apparently influenced by electron-hole interaction, as postulated by Elliott. In the actual edge region, absorption falls off exponentially with decreasing photon energy, the steepness at 300°K being 197 e${\mathrm{V}}^{-1\mathrm{}}$ for E∥C and 267 e${\mathrm{V}}^{-1\mathrm{}}$ for E ⊥ C. The steepness for each polarization increases by only 14% on cooling to 100°K.