Investigation of ion-bombardment effects on the formation of voids during deposition of a-Ge : H

In this work, positron annihilation (PA) and infra-red (IR) spectroscopies are combined to obtain information on the H bonding and the void size distr ibution as a function of deposition parameters (substrate temperature and i on-bombardment) during reactive ion-beam sputtering deposition (IBSD) for t he growth of a-Ge : H films. For a-Ge:H films obtained at substrate tempera tures between 180 degrees C and 260 degrees C without ion bombardment of th e growth surface, PA studies reveal low-value valence (S) parameters and hi gh core (W) parameters as compared with films grown under less-favorable co nditions. These data indicate a relatively low concentration of large voids , the annihilation process being controlled mainly by trapping at vacancies . IR and PA measurements on IBSD samples subjected to in-situ ion-bombardme nt during growth indicate ion irradiation of the growth surface as a major factor responsible for large void formation. It can thus be concluded that rather compact a-Ge:H films can be obtained by IBSD at substrate temperatur es between 180 degrees C and 260 degrees C, by minimizing the ion bombardme nt of the growth surface. (C) 1999 Elsevier Science B.V. All rights reserve d.