On the Structural and Optical Properties of Sputtered Hydrogenated Amorphous Silicon Thin Films

TL;DR

This study investigates how hydrogen partial pressure and thermal annealing affect the structural and optical properties of hydrogenated amorphous silicon thin films prepared by sputtering, revealing optimal conditions for improved film quality.

Contribution

It provides new insights into the effects of hydrogen pressure and annealing on the optical and structural characteristics of a-Si:H films, using grazing X-ray reflectometry.

Findings

Low hydrogen pressures saturate dangling bonds, high pressures create defects.

Thermal annealing improves structural quality.

Hydrogen protects against oxidation initially, but not after prolonged ambient exposure.

Abstract

The present work is essentially focused on the study of optical and structural properties of hydrogenated amorphous silicon thin films (a-Si:H) prepared by radio-frequency cathodic sputtering. We examine separately the influence of hydrogen partial pressure during film deposition, and the effect of post-deposition thermal annealings on the main optical characteristics of the layers such as refraction index, optical gap and Urbach energy. Using the grazing X-rays reflectometry technique, thin film structural properties are examined immediately after films deposition as well as after surface oxidation or annealing. We show that low hydrogen pressures allow a saturation of dangling bonds in the layers, while high doses lead to the creation of new defects. We show also that thermal annealing under moderate temperatures improves the structural quality of the deposited layers. For the films examined just after deposition, the role of hydrogen appears in the increase of their density. For those analysed after a short stay in the ambient, hydrogen plays a protective role against the oxidation of their surfaces. This role disappears for a long time stay in the ambient. Keywords Amorphous silicon, Grazing incidence X-rays, Hydrogen, Optical properties, Penetration depth, Reflectometry, Thermal annealing, Thin films. PACS Numbers 61.10.K - 61.43.D - 68.55.JK - 68.55.81.15.A