It proves difficult to obtain a set of protocrystalline silicon materials with different characteristics from the same deposition chamber to study the exact nature of these transition region materials. Hot-wire deposited protocrystalline silicon was thus isochronically annealed at different temperatures to investigate the bonded hydrogen configurations and structural disorder. Modeling of optical reflection and transmission spectra with Scout (R) yielded the optical parameters and infrared spectroscopy confirms that bonded hydrogen remains in the material, with the exception of a longer anneal of six hours at 520 degrees C. Sub bandgap absorption as inferred from photothermal deflection spectroscopy was related to these characteristics. (C) 2011 Elsevier B.V. All rights reserved.