The role of hydrogen dilution of silane and phosphorus doping on hydrogenated microcrystalline silicon (μc-Si:H) films prepared by hot-wire chemical vapor deposition (HW-CVD) technique

The electrical, structural and optical properties of undoped and phosphorus doped muc-Si:H films prepared by a HW-CVD technique have been studied. The hydrogen (H-2) dilution of silane has been varied carefully to produce undoped muc-Si:H films. The amorphous-to-microcrystalline transition was observed for a hydrogen dilution ratio >0.75. The phosphorus doped muc-Si:H films were deposited by varying the phosphine (PH3) gas flow rate. The structural properties of these films have been investigated by Raman spectroscopy, low angle X-ray diffraction spectroscopy and Fourier transform infrared vibrational spectroscopy. Electrical characterization has been carried out by dark conductivity and charge carrier activation energy measurements. The phosphorus doped muc-Si:H films showed that the addition of PH3 to the source gases promotes the growth of crystallinity. The increase in crystallite size and crystalline volume fraction with the addition of PH3 to the source gases indicates that it enhances the crystallization of the muc-Si:H film. Low angle XRD studies shows that the PH3 doped muc-Si:H does not show any preferential orientation crystallites. For optimized deposition conditions PH3 doped muc-Si:H films with high dark conductivity (0.4 S/cm), low activation energy (0.03 eV) and high band gap (1.82 eV) were obtained with a high deposition rate (13 Angstrom /s). However, for these optimized conditions, the hydrogen content was relatively large (8.3 at.%). (C) 2001 Elsevier Science B.V. All rights reserved.