OXYGEN ADSORPTION-DESORPTION EFFECT ON THE ELECTRICAL-PROPERTIES OF A-SI-H LAYERS

Oxygen interaction with hydrogenated amorphous silicon a-Si:H thin fil ms is studied using conductance measurements and X-ray photoelectron s pectroscopy (XPS) analysis. Oxygen adsorption on an a-Si:H surface at 160 degrees C gives a reversible variation of the conductance, The bef ore-adsorption conductance value is restored after desorption at 220 d egrees C. XPS analysis of the film surface shows the presence of a thi ck film (similar to 10 Angstrom) of silicon bonded to 1, 2, 3 or 4 oxy gen. These results are explained by the effect of a negative charge in duced at the surface. This charge depends on the equilibrium between t he different oxidation states of the amorphous silicon surface detecte d by XPS measurements.