C/sub 60//a-C superlattice structures for solar cell applications

C/sub 60//amorphous carbon (a-C) superlattice structures were fabricated by shutter controlled molecular beam deposition. A-C layers were transformed from C/sub 60/ by nitrogen ion bombardment. The dark and photo conductivity of C/sub 60//a-C superlattice structures were measured by gap-cell structure. The resulted films show high resistivity, and the photosensitivity ratio ranged from 9/spl sim/16. It is thought that such low photosensitivity is caused by high defect density of 2.7/spl times/10/sup 21/ cm/sup -3/ in the a-C layers. Use of hydrogen plasma in C/sub 60/ amorphization process, instead of nitrogen, reduces the spin defect density in two orders of magnitude. Hydrogen atoms effectively reduce the defect density of a-C films by etching the weak carbon bond structures and/or passivating the dangling bonds.