OPTICAL-PROPERTIES OF HYDROGENATED AMORPHOUS-SILICON FILMS DOPED WITHFLUORINATED GASES

Doped amorphous silicon films were prepared by plasma-enhanced chemica l vapour deposition of silane and hydrogen mixtures, using phosphorus pentafluoride (PF5) and boron trifluoride (BF3) as dopant precursors. The films were studied by UV-vis spectroscopy and their photo and dark conductivity were measured, the latter as a function of temperature. The optical gap of the n-type samples, doped with PF5, diminished as t he concentration of this gas in the plasma was increased. However, the optical gap of p-type samples, doped with BF3, did not show any appre ciable optical gap decrease as the concentration of BF3 was varied fro m 0.04% to 4.7%. The dark conductivity of the p-type films at these ex tremes of the doping range were 7.6 X 10(-10) and 3.5 X 10(-1) Ohm(-1) cm(-1), respectively.