Properties of Sputtered A-ge and A-ge:h Thin Films

Title of Thesis : Properties of sputtered a-Ge and a-Ge:H thin films Hanjin Cho, Master of Science in Electrical Engineering , 1987 Thesis directed by : Dr. Kenneth S. Sohn. The effect of the amorphous and glassy structure of amorphous germanium films on their electrical characteristics was investigated experimentally. The films were deposited onto silicon substrates using a modified MRC 8800 triode sputtering system. The Poole-Frenkel and Schottky mechanisms are discussed in detail and the shortcomings of the accepted picture of the former in amorphous materials are dealt with. It was concluded on the basis available evidence that the current flow in amorphous germanium favors the Poole-Frenkel mechanism at high fields. Amorphous hydrogenated germanium films which were deposited by bias sputtering were characterized by measuring the infrared absorption. The films have absorption peaks,as expected, at 1950 cm-1 and at 570 cm-1 due to GeH2 bonding and at 1880 cm-1 due to GeH bonding. A method was described for determining the optical constants of a thin film deposited on a nonabsorbing window using a single set of transmittances over an absorption band. The method depends on the fact that the phase shift of the transmitted radiation can be determined from the transmittance by a Kramers-Kronig transform. The transmittance data of a-Ge:H and sputtered silicon nitride films were used to calculate their optical constants by this method. In a-Ge:H films, the value of the calculated refractive index in the k=0 region was not reasonable. However, for Si 3N4 films, the calculated absorption coefficient was consistent with the experimental results. PROPERTIES OF SPUTTERED a-Ge and a-Ge:H THIN FILMS