Optical and electrical properties of doped amorphous silicon suboxides

Abstract

In this work we investigate the effects of thermal annealing on the optical and electrical properties of doped amorphous silicon suboxide $(a\ensuremath{-}{\mathrm{SiO}}_{x}:\mathrm{H})$ samples prepared by plasma-enhanced chemical-vapor deposition. Efficient p- and n-type doping is possible up to a concentration of 10 at. % oxygen. Structural properties of the films are deduced from hydrogen evolution measurements and infrared spectroscopy. Changes in the microscopic structure of the amorphous network upon thermal annealing at low annealing temperatures cause a dopant activation of the p-type samples. The resulting increase of the dark conductivity becomes less pronounced for increasing oxygen content of the films, but still comprises almost two orders of magnitude for samples with 9 at. % oxygen. N-type suboxides do not show such doping activation upon thermal annealing. Thermal annealing at higher temperatures leads to an effusion of hydrogen, reducing the optical band gap ${E}_{04}$ of the samples. The dependence of ${E}_{04}$ on the hydrogen content for amorphous suboxides with different oxygen content is investigated and found to be similar to that of amorphous silicon.