Ge : Si : O evaporated alloys as a thermosensitive layer for large area bolometers

A study of the composition and properties of amorphous Ge:Si:O thin films d eposited at low temperature by reactive coevaporation is presented. Films w ith various compositions are obtained by separately controlling the evapora tion rates of germanium and silicon. The composition of films is measured b y combining Rutherford backscattering spectrometry (RBS), nuclear reaction analysis (NRA) and energy dispersive X-ray analysis (EDX) techniques. Films are characterized by FTIR absorption spectroscopy, VIS-NIR transmittance a nd temperature behaviour of the electrical resistivity. The analysis of all experimental data shows that oxygen incorporation depends on the silicon c ontent in the films. Oxygen atoms appear mainly bonded to silicon and not t o germanium. An uniformed distribution rather than a cluster structure of s ilicon oxide into a germanium matrix is suggested. Both optical band gap en ergy and thermal coefficient of the resistivity vary with composition of fi lms. Preliminary studies of thin films with similar composition obtained us ing reactive sputtering from a composite target evince the coexistence of S i-O and Ge-O bonds. (C) 1999 Elsevier Science S.A. All rights reserved.