Study of photoconductivity in TBP doped n-type hydrogenated amorphous silicon using Argon as carrier gas

摘要

In the present paper, photoconductivity, sigma(ph), of n-type a-Si:H films, obtained by using tertiarybutylphosphine (TBP) as a dopant are reported. The films were obtained by adding TBP vapour to silane (SiH4) gas in ratios varying from 10(-3)% to 3% in an rf glow discharge (plasma lab mu P) process using Ar as the carrier gas. Room temperature photoconductivity is found to initially increase with dopant concentration, is a maximum for TBP/SiH4 ratio near 10(-2)% and decreases as the TBP/SiH4 ratio is increased from 10(-1)% to 3%. A correlation is found to exist between photoconductivity and position of the dark Fermi level. Photosensitivity is found to increase as the TBP/SiH4 ratio increases from 10(-3)% to 10(-2)% and decrease as the dopant concentration is increased to 1%, but for a heavily doped sample (TBP/SiH4 = 3%) the photosensitivity is found to increase again. The temperature variation of photoconductivity is measured over the temperature range 190 to 400 K. The intensity dependence of the photoconductivity indicates the existence of bimolecular recombination. The spectral response of the photoconductivity is qualitatively similar for different doping ratios. A peak is observed at an energy of 2.0 eV for all the samples. (C) 1998 Elsevier Science B.V. All rights reserved. [References: 17]