Dark and photoconductivity of TBP doped n-type a-Si:H

Abstract

In the present paper dark and photoconductivity of n-type a-Si:H films, obtained by using tertiarybutylphosphine (TBP) as dopant instead of phosphine, which is difficult to handle because of its high toxicity and pyrophoricity, have been reported. The films were obtained by adding TBP vapor to Silane gas in ratio varying from 10 −1% to 2% in an rf glow discharge process using He as carrier gas. The activation energy and pre-exponential factor have been determined as a function of TBP/SiH 4 gas phase ratio by measuring the conductivity as a function of temperature. The conductivity is found to be singly activated in the temperature range 350 to 450 K for samples having TBP/SiH 4 ratio as 1% and 2%. In the present work the activation energy is found to increase from 0.21 to 0.37 eV as the TBP/SiH 4 ratio increases from 10 −1% to 2%. The optical bandgap (1.98 eV) has been found to be constant for samples with different TBP/SiH 4 ratio. Intensity variation of photoconductivity indicates bimolecular recombination to be the dominant mechanism. Photosensitivity is found to decrease with in TBP/SiH 4 ratio.