Electron- and photon-induced conductivity in chalcogenide glasses

A comprehensive study of the effects of electron and photon beams on the electrical properties of rf-sputtered chalcogenide-glass films of composition Te40As35Si15Ge7P3 has been carried out. Optical results indicate that the material has a gap near 1.1 eV. Four major conclusions follow from a detailed investigation of the field and polarity dependence of the photocurrent: (1) the exponential increase of dark conductivity with electric field intensity is a carrier concentration rather than a mobility effect; (2) internal fields exist at molybdenum-chalcogenide junctions; (3) hole conduction dominates electron conduction at room temperature; (4) the chalcogenide bands bend up at the interface with molybdenum electrodes. Electron-beam-induced conductivity (EBIC) resulting from bombardment by 5–20-keV electrons has also been studied as a function of applied voltage on these films. A threshold energy of about 7 keV is necessary to obtain an EBIC signal, resulting from a schubweg of the order of 1000 Å and a film thickness of 1 μm. The photoconductivity and EBIC results are consistent and indicate that the product of mobility and lifetime for the carriers in these materials is approximately 2×10−10 cm2/V. This corresponds to carrier lifetimes of the order of 2×10−11 sec. The drift mobility is trap controlled and of the order of 2×10−5 cm2/V sec.