Boron-Doped Polycrystalline Silicon Thin Films Deposited by CVD on Glass Substrates

Abstract

In this work, we use atmospheric pressure thermal chemical vapour deposition (AP-CVD) to deposit thin poly-Si films on glass substrates. The CVD reactor is a batch-type hot-wall reactor, employing SiHCl3 as a precursor, BBr3 as a doping agent and H2 as a carrier and reaction gas. We use a temperature of 850 ºC, and a commercial aluminosilicate float glass as a substrate. The films that we obtain are homogeneous and well adhered to the substrate. Scanning electron microscopy (SEM) is used to observe the surface and the cross-section of the samples. We find a columnar structure suitable for the electrical conduction in photovoltaic cells. X-ray diffraction reveals a strong (2 2 0) preferential orientation of the films, which is indicative of a low density of intra-grain defects. Dark conductivity measurements as a function of temperature show that the films can be grown intrinsic, slightly ptype or highly p-type. Activation energies between 0.61 and 0.03 eV have been obtained. In conclusion, our results demonstrate the feasibility of directly depositing doped poly-Si thin films on glass substrates at intermediate temperatures, with characteristics that make them appropriate for photovoltaic applications.