Compact hydrogenated amorphous germanium films by ion-beam sputtering deposition

We explore reactive ion-beam sputtering deposition (IBSD) for the growth of a-Ge:H films. It is shown that compact a-Ge:H films can be obtained by IBSD at substrate temperatures between 180°C and 220°C by minimizing the ion bombardment of the growth surface. The infrared (IR) spectra of the best materials, as far as device applications are concerned, so-far obtained show no poly-hydride nor surface-like contributions to the Ge–H dipole vibration bands. Positron annihilation (PA) spectroscopy studies of these samples reveal smaller valence (S) parameters and larger core (W) parameters as compared with the films grown under less-favorable conditions, which indicate a relatively smaller concentration of the largest voids, the annihilation process being controlled mainly by trapping at small vacancy clusters or monovacancies. Similar IR and PA measurements on in situ ion-bombarded IBSD and RF-sputtered samples indicate that ion irradiation is a main factor in large void formation.