Heavy-ion elastic-recoil detection analysis of doped-silica films for integrated photonics

Photosensitive silica films, in which a permanent refractive index change is induced by exposure to ultra-violet (UV) light, are of interest for the fabrication of integrated photonic devices and circuits. Such films, consisting of Ge- and Sn-doped silica, are being fabricated at the Australian National University (ANU) by a plasma assisted deposition technique known as Helicon Assisted Reactive Evaporation (HARE). The initial refractive index of these films is related to their stoichiometry and can be altered further by controlled exposure to UV light . Contaminants introduced into the films during deposition can degrade their optical properties and are therefore also of interest. Hydrogen is of particular concern as it causes optical absorption in the wavelength range of interest for communications applications (1.3-1.5μm). High-energy heavy ion elastic recoil detection (ERD) analysis enables the detection of a broad range of elements with almost constant sensitivity. A variety of recoil detection systems have been developed for this purpose, including time-of-flight systems, magnetic spectrometers, and quadrupole spectrometers. However, these are often restricted to small acceptance solid angles. Beam-induced sample modification, such as hydrogen release, can therefore be a serious limitation. The use of a position sensitive gas ionization detector overcomes these limitations for a range of import ant applications by operating with a large solid angle and correcting the kinematic energy spread of the ions over large acceptance angles to provide ≤1% energy resolution. In this study, heavy-ion ERD employing a novel position sensitive gas ionization detector is used to characterize the composition, thickness, uniformity and hydrogen content of Ge- and Sn- doped silica films. The technique is shown to provide this information in a single measurement