The effect of main-ion-beam parameters on some properties of a-Si:H prepared by ion-beam-assisted reactive evaporation

Abstract

This paper reports the effect of the ion-beam-source parameters on the properties of a-Si:H deposited by ion-beam-assisted reactive evaporation with silane as the feedthrough gas. It is observed that the hydrogen concentration (CH) in the resulting film is determined mainly by the ion-beam intensity at the substrate for a fixed substrate temperature (about 60 °C), a fixed silane partial pressure (2 × 10−4 Torr (1 Torr = 133.3 Pa)) and a fixed deposition rate (8 nm min−1). As CH increases from 15 to 34 at.% in films containing 3 at.% carbon, the SiH stretching mode in the IR absorption spectrum shifts from 2000 to 2055 cm−1. The ratio of the photoconductivity to dark conductivity depends not only on the incident ion density (or CH), but also on the ion-beam energy. Near an ion energy of 200 eV and a CH of 24 at.%, this ratio goes through a maximum (~1 × 105). Electron-diffraction patterns show that the films are amorphous, and microscopic observations by transmission electron microscopy illustrate that when suitable ion-beam parameters are used, the porosity of the films is reduced.