Energy-resolved photon flux dependence of the steady state photoconductivity in hydrogenated amorphous silicon: Implications for the constant photocurrent method

SCHMIDT, J.A.; KOROPECKI, R.R.; ARCE, R.D.; RUBINELLI, F.A.; BUITRAGO, R.H.

THIN SOLID FILMS

ELSEVIER SCIENCE SA

Año: 2000 vol. 376 p. 267 - 274

0040-6090

We have studied the photon flux dependence of the steady state photoconductivity in intrinsic and lightly boron-doped hydrogenated amorphous silicon samples illuminated with monochromatic light of sub-bandgap energy. We also report measurements of the sub-bandgap absorption coefficient carried out by using the dc constant photocurrent method (CPM) under different constant values of the photocurrent. We show that the exponent of the power law relation between the photocurrent and the photon flux (which we name λ) depends on the photon energy. This result contradicts one basic hypothesis of the CPM. As a consequence of this fact, the absorption coefficient measured with the CPM is dependent on the constant photocurrent chosen to perform the measurement. Computer simulations based on a complete model for the absorption process reproduce both of these experimental results. We conclude that this model can be used to handle CPM data in order to obtain the actual sub-gap absorption spectra.