Effects of hydrogen pressure on hydrogenated amorphous silicon thin films prepared by low-temperature reactive pulsed laser deposition

Abstract

We deposit intrinsic hydrogenated amorphous silicon (a-Si:H) thin films by reactive pulsed laser deposition, for various hydrogen pressures in the 0-20 Pa range, at a low deposition temperature of 120C, and investigate the hydrogen incorporation, structural, optical, and electrical properties of the films, as a function of the ambient hydrogen pressure. The film thickness decreases linearly as the hydrogen pressure increases. The hydrogen content of the films is determined by infrared spectroscopy and the optical bandgap from UV-Vis-NIR transmittance and reflectance measurements. Electric measurements yield the dark conductivity of the films. The hydrogen concentration of the films lies in the 10^21-10^22 cm^(-3) range and increases with the hydrogen pressure until the latter reaches 15 Pa, beyond which the hydrogen concentration decreases. The optical bandgap and dark conductivity follow the hydrogen concentration variation of the films. The dark conductivity lies in the 10^(-9)-10^(-10) S/cm range. An unusually wide optical bandgap of 2.2-2.6 eV is observed.