ELECTRONIC CONDUCTION IN ION IMPLANATED AMORPHOUS CARBON THIN FILMS

Abstract

The electronic conduction mechanism occuring in amorphous thin films is quite complicated. In amorphous carbon films it is further exacerbated by the rich diversity of its microstructure as well as the large number of gap states present in the films. One of the main reasons for the tunability of the optical band gaps of these films not being exploited in active devices, has been the inability firstly to reduce the gap states to an acceptable level, and secondly finding suitable dopants that are electrically active at room temperature. The large number of gap states in the films further exacerbates its problems by not allowing suitable barriers (eg. Schottky) to be formed on to the amorphous carbon films. In this paper we hope to first divide the amorphous carbon thin films into two main categories. Namely, diamond-like carbon films which have a high precentage of C-C sp 3 bonding, and polymer-like carbon films that also have a high percentage of sp 3 bonding which is a mixture of C-C and C-H bonds, and have a high percentage of hydrogen as well as large optical band gaps. Recent results based on ion implantation using ions such as N, B, C will be contrasted to in-situ dopant incorporation via a gaseous source., and is shown to be a very powerful technique of modifying the conduction properties. It will be shown that in the diamond-like films the conduction properties are usually controlled via Poole-Frenkel type defect conduction, while for the polymer-like films it is more a space charge based bulk and possibly, barrier controlled process. But, due to the large band gaps of these films it is difficult to distinguish between the bulk effects and the barrier effects.