Post Annealing Studies of C 60 Ion Implanted Thin Films
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Post Annealing Studies Of C60 Ion Implanted Thin Films Nethaji Dharmarasu, Kannan L. Narayanan, Nabuaki Kojima, Yoshio Ohshita and Masafumi Yamaguchi, TOYOTA TECHNOLOGICAL INSTITUTE, 2-12-1 HISAKATA, TEMPAKU, NAGOYA 4688511, JAPAN ABSTRACT Physical properties of multiple-energy B-ion implanted C60 thin films were investigated for various doses. Fourier Transform Infra-red Spectroscopy (FTIR) results indicate the structural transformation of C60 to amorphous carbon phase during implantation. The conductivity type of the implanted films is found to be p-type and the conductivity measurements reveal a dramatic increase in the conductivity with ion implantation. Temperature dependent conductivity shows the semiconducting nature of the B-ion implanted films. The optical absorption coefficient and optical gap of the implanted films have been observed as a function of B-ion dose. Measurements on implanted films subjected to thermal annealing indicate the removal of the defects caused during the implantation. Ion implantation-induced defects are found to partially annihilate with the annealing temperature. Electrical conductivity and optical gap are determined in the post-implanted films. The observation of the systematic increase in the conductivity of the annealed films is due to the removal of the defects and the formation of defect free boron impurity acceptor.
INTRODUCTION Recently ion implantation in carbon material has attained an enormous interest for its opto-electronic device applications. Investigation on C60 progressed rapidly in wide areas of science and technology because of its novel physical properties. Furthermore, as the band gap energy of C60 is around 1.6 eV to 1.8 eV it is a suitable material for the fabrication of solar cell. Since undoped C60 is a highly insulating n-type material, p-type formation and conductivity control of C60 are necessary for its photovoltaic applications. Doping can be achieved either by a chemical route or by physical means such as diffusion and ion implantation. Ion implantation effects in C60 thin films are reported by various researchers [1-3]. These investigations include the ion implantation induced polymerization and subsequent amorphization. Fu et al [4] have reported n-and p-doping into C60 films by ion implantation. In the present case the doping of C60 has been done by means of ion implantation as the depth distribution and doping density of C60 can easily be controlled by the ion energy and the ion dose, respectively. However various physical properties like optical, electrical and structural properties of the fullerene thin films will be modified due to ion implantation. There are few reports in the direction of its applications towards solar cells. The purpose of the present study is to investigate boron-ion implantation and thermal annealing effects in C60 and to increase the conductivity to increase the efficiency of a carbon-based solar cell.
R9.8.1/O14.8.1
EXPERIMENTAL DETAILS The C60 films were prepared on quartz and silicon substrates at a substrate tempe
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