Electronic and optical properties of hot-wire-deposited microcrystalline silicon

We conducted a study on undoped and doped hydrogenated microcrystalline silicon (mu c-Si) samples deposited by hot-wire chemical vapor deposition for determination of the structural, electronic and optical properties. Light scattering, investigated by total and specular transmission and reflection, as well as angular resolved measurements, results mainly from the surface but with an intrinsic contribution from the interior. The optical properties resemble that of monocrystalline Si: the refractive index in the visible, the reflectance peaks in the near ultraviolet which may only appear after surface polishing, and the absorption coefficient which is larger than in monocrystalline silicon and varies with sample thicknesses. Depending on the doping level, the dark conductivity prefactor and activation energy exhibit either normal or anti-Meyer-Neldel rule behavior. The mobility-lifetime product from steady state photoconductivity strongly depends on the position of the Fermi energy with a minimum for low p-type doping, suggesting the importance of information on the Fermi energy if the mobility-lifetime product is given as an indicator for material quality of microcrystalline Si. (C) 1998 Elsevier Science B.V. All rights reserved.