GROWTH AND NEAR-ULTRAVIOLET OPTICAL-ABSORPTION CHARACTERISTICS OF SPUTTER DEPOSITED NOMINAL GERMANIA

Films were grown on unheated 〈111〉-cut silicon and fused silica substrates by reactive sputter deposition using a germanium target and Ar/O2 discharges operated at 100-400 W rf forward power. Ge(O) and nominal germania phases were identified on the basis of infrared absorption spectra. The regions of discharge power-sputtering gas O2 content space in which Ge(O) and nominal germania phases were formed were determined. The Ge(O)-nominal germania phase boundary shifted to higher gas O2 content with increasing discharge power. Nominal germania growth was concurrent with an abrupt decrease in growth rate, explained in terms of germanium target surface oxidation. Within the range of power density used in this study, 0.8-3.2 W/cm2, near-ultraviolet (E = 4.63-6.37 eV) absorption characteristics of nominal germania grown on fused silica were independent of gas O2 content and dependent upon discharge power. The results are compared with recent studies of (1) films grown at the same power but higher power density, and (2) bulk fused germania glass. © 1990.