DARK AND PHOTOCONDUCTIVITY OF TBP DOPED N-TYPE A-SI-H

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 a nd pyrophoricity, have been reported. The films were obtained by addin g 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/ SiH4 gas phase ratio by measuring the conductivity as a function of te mperature. The conductivity is found to be singly activated in the tem perature range 350 to 450 K for samples having TBP/SiH4 ratio as 1% an d 2%. In the present work the activation energy is found to increase f rom 0.21 to 0.37 eV as the TBP/SiH4 ratio increases from 10(-1)% to 2% . The optical bandgap (1.98 eV) has been found to be constant for samp les with different TBP/SiH4 ratio. Intensity variation of photoconduct ivity indicates bimolecular recombination to be the dominant mechanism . Photosensitivity is found to decrease with increase in TBP/SiH4 rati o.