The influence of hydrogen and argon pressure on composition and optoelectronic properties of sputtered a-Si 1− xGe x:H ( x ≈ 0.4)

Abstract

The composition and the defect density of a-Si 1− x Ge x :H films ( x ≈ 0.4) prepared by magnetron sputtering of a composite target under varying hydrogen and argon partial pressure were investigated by Rutherford backscattering spectrometry (RBS), elastic recoil detection (ERD), infrared spectroscopy, electron spin resonance (ESR) and photothermal deflection spectroscopy (PDS). The incorporation of hydrogen is well described by Moustakas' empirical relation and results in preferential SiH bonding and preferential plasma etching of Si during the film growth. By contrast with sputtered a-Si:H and a-Ge:H where good agreement of the data is observed, the hydrogen concentration of the alloy determined by ERD and IR spectroscopy differs by a factor of two. Hydrogenation lowers the film's spin density to typically 3 × 10 18 cm −3 which is about a factor of ten above the value obtained from PDS measurements. The optical properties static refractive index and Tauc gap vary linearly with the films hydrogen content in the range of 3.8-3.4 and 1.2 eV–1.55 eV, respectively. Hydrogenation causes a decreases of the dark conductivity from 10 −6 (Ω cm) −1 to a minimum of 10 −10 (Ω cm) −1 and an increase of the normalized photoconductivity to a maximum of ημτ = 5 × 10 −8 cm 2/V.