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 degrees C and 220 degrees 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. (C) 2000 Elsevier Science B.V. All rights reserved.