Transition from amorphous semiconductor to amorphous insulator in hydrogenated carbon-germanium films investigated by IR spectroscopy

Thin a-GeXC1−X:H plasma polymerized films, depending on deposition conditions, can be produced in two very different structures, namely amorphous semiconductor and amorphous insulator. The transition from amorphous insulator to amorphous semiconductor is related to the formation of germanium nanoclusters due to ions bombarding the surface of the growing material. This paper concentrates on investigations of the transition by means of IR spectroscopy. To this end a quantitative analysis of IR spectra obtained for thin films deposited on silicon substrate has been described and used for estimation of hydrogen atom concentration and bonding in the investigated material. It was found that the probability that a given H atom is bonded to a germanium or to a carbon atom is almost the same. This conclusion is true both for a-S and a-I films. The average concentration of hydrogen in the investigated material was found to be about 2.4-3.4 × 1022 cm−2 which means that there are two times more atoms of the carbon family than hydrogen atoms in the film structure.