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 distribution as a function of deposition parameters (substrate temperature and ion-bombardment) during reactive ion-beam sputtering deposition (IBSD) for the growth of a-Ge:H films. For a-Ge:H films obtained at substrate temperatures between 180°C and 260°C without ion bombardment of the growth surface, PA studies reveal low-value valence (S) parameters and high core (W) parameters as compared with films grown under less-favorable conditions. 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-bombardment 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 temperatures between 180°C and 260°C, by minimizing the ion bombardment of the growth surface.