Electrical properties of amorphous chalcogenide/silicon heterojunctions modified by ion implantation

Abstract

Doping of amorphous chalcogenide films of rather dissimilar bonding type and resistivity, namely, Ga-La-S, GeTe, and Ge-Sb-Te by means of ion implantation of bismuth is considered. To characterize defects induced by ion-beam implantation space-charge-limited conduction and capacitance-voltage characteristics of amorphous chalcogenide/silicon heterojunctions are investigated. It is shown that ion implantation introduces substantial defect densities in the films and their interfaces with silicon. This comes along with a gradual decrease in the resistivity and the thermopower coefficient. It is shown that conductivity in GeTe and Ge-Sb-Te films is consistent with two-type carrier conduction model. It is anticipated that ion implantation renders electrons to become less localized than holes leading to electron conductivity in certain cases as, for example, in GeTe. The modification of electronic properties which stems from the ion-solid interaction processes results in the modification of the composition of the films as identified by elemental analyses with the help of Rutherford Backscattering Spectrometry. At the same time, much higher interface trap densities are observed in the implanted chalcogenide/silicon interfaces. In terms of interface trap built-up, ion implantation influences Ge-Sb-Te and Ga-La-S interfaces with silicon distinctly different. Much higher density of acceptor-like interface trap is observed in Ga-La-S/Si interfaces suggesting the ion-beam induced interface traps are not solely due to silicon dangling bond defect.

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ORCID for D.W. Hewak: orcid.org/0000-0002-2093-5773

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