Amorphous GexSi1−xOy sputtered thin films for integrated sensor applications

Abstract

In this work, we analyze the electrical behavior of amorphous GexSi1−xOy thin films to be used as sensitive layers in integrated bolometers. The GexSi1−xOy films were grown by reactive sputtering of a Ge0.85Si0.15 target using a mixture of argon and oxygen. The films were characterized by measuring the composition, the optical gap, the resistivity, and the activation energy of the electrical conductivity. We analyzed the effects of the sputter gas composition, the rf power applied to the target, and the bias voltage applied to the substrate on the properties of the films. A homogeneous amorphous semiconductor was obtained, in which oxygen is bonded to both silicon and germanium atoms. The optical gap, the resistivity, and the activation energy of the resistivity increase monotonically with the total oxygen content of the films. The application of a bias voltage to the substrate causes slight compositional changes in the films and modifies the band structure of the amorphous semiconductor. As a consequence, the electrical resistivity and the activation energy are reduced with increasing bias. Under optimum experimental conditions, GexSi1−xOy layers with moderate electrical resistivities around 104 Ω cm and thermal coefficients as high as 5% K−1 have been obtained.