Doped Polycrystalline Silicon Thin Films Deposited on Glass from Trichlorosilane**

Abstract

Atmospheric pressure (AP) thermal CVD is used to deposit thin poly-Si films on glass substrates. Also produced are heterojunction solar cells carrying out the deposition on c-Si wafers. A batch-type hot-wall reactor, employing SiHCl₃ as a precursor, H₂ as a carrier and reaction gas, BBr₃ as a p-type doping agent, and PCl₃ as a n-type doping agent, is used. The films obtained are homogeneous and well-adhered to the substrate. Samples are structurally characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), reflectance spectroscopy in the UV-vis region, X-ray diffraction (XRD), and Raman spectroscopy (RS). The electrical characterization includes conductivity measurements as a function of temperature, and Hall effect measurements. For the p-doped samples, XRD reveals a strong (220) preferential orientation of the films, while the n-doped samples lack columnar structure or preferential orientation. RS and UV-reflectance confirm a high crystalline fraction. Dark conductivity measurements as a function of temperature show that the films can be grown intrinsic, p-type or n-type. Activation energies between 0.61 and ∼0 eV are obtained, with reasonable values for the carrier mobilities. For the solar cells, relatively high values of V_OC(∼507 mV) and J_SC (∼29.6 mA cm⁻²) are measured. In conclusion, these results demonstrate the feasibility of directly depositing doped poly-Si thin films on glass and c-Si substrates at intermediate temperatures, with interesting characteristics for photovoltaic applications.