Effect of minor impurities on the electrical properties of Se and Se containing glasses

A number of selenium glasses doped with halogens (Cl, Br, I), in the range of few p.p.m. up to U at %, were prepared in an oxygen-free atmosphere by melt quenching. D.C. conductivity as a function of the temperature was measured and for the higher impurity concentration samples the measurement of the thermoelectric power, D.C. photoconductivity, electron spin resonance and optical absorption coefficient was also undertaken. Other supporting experiments included infrared spectrometry, differential scanning calorimetry, energy dispersive analysis of X-Rays and field effect. X-Ray diffraction was used to check the lack of long-range order in each sample. A general review of amorphous semiconductors is included with particular reference to their electronic and optical properties and the importance of defect states. Results demonstrate the large effect of halogens on conductivity and that the conduction remains p-type with no observable E.S.R. signal. Data obtained are compared with those available in the literature and discussed within the framework of the CFQ-Mott theory. Tentative interpretation of the results is made via a "dangling bonds model" assuming a single particle acceptor level. Additional complementary studies of a number of chalcogenide glasses doped with Br are also included. The effect of several other additives (Ag, Cu, Tl, Na, Sb, Al, Bi) on the D.C. conductivity and other properties of vitreous selenium is briefly investigated