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

• Published in: Thin solid films 2000-11, Vol.376 (1), p.267-274
• Main Authors: Schmidt, J.A., Koropecki, R.R., Arce, R.D., Rubinelli, F.A., Buitrago, R.H.
• Format: Article
• Language: English
• Subjects: Amorphous materials; Amorphous semiconductors; glasses; Amorphous semiconductors; glasses; nanocrystalline materials; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electronic transport phenomena in thin films and low-dimensional structures; Exact sciences and technology; Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity); Optical constants: refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity; Optical properties; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of bulk materials and thin films; Optical properties of specific thin films; Photoconduction and photovoltaic effects; Photoconduction and photovoltaic effects; photodielectric effects; Photocurrent spectroscopy; Physics; Silicon
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/S0040-6090(00)01193-7

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.