Characterization of thin polycrystalline silicon films deposited on glass by CVD

Abstract

We deposited polycrystalline silicon (poly-Si) thin films on commercial float glass by chemical vapour deposition from trichlorosilane at temperatures between 735 and 870 • C. The structural properties of the films were evaluated by means of scanning electron microscopy, x-ray diffraction, atomic force microscopy, reflectance in the ultraviolet region and Raman spectroscopy. The electrical characterization involved measurements of dark conductivity and photoconductivity as a function of temperature, Hall effect, ambipolar diffusion length from the steady-state photocarrier grating technique and density of defects by means of modulated photoconductivity. By using boron tribromide as a doping agent, degrees of doping ranging from intrinsic to clearly p-doped were obtained. The process, the reactants and the substrate used are of low cost, and proved to be adequate for direct poly-Si deposition, giving films of good structural and electrical properties.

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

“…The result is shown in Figure (blue diamonds, right scale). The intrinsic samples are in compressive stress (around −200 MPa), as we have found previously . The less‐doped samples are in tensile stress, the value for the least‐doped sample (245 MPa) being the highest of the series of samples.…”

“…The average grain size is about 190 nm, independent of the BBr 3 concentration. Within the doping range of our experiments, this average grain size is lower than that of undoped samples (around 270 nm) deposited with the same procedure and the same parameters . This means that the addition of boron increases the nucleation rate.…”

“…In previous works, we have shown that intrinsic poly‐Si layers, exhibiting good structural and optical properties, can be deposited by APCVD on glass substrates . The next step towards the production of solar cells is the deposition of doped layers.…”

Density and mobility effects of the majority carriers in organic semiconductors under light excitation

“…Despite this drawback, the analysis of the MPC data can provide important parameters (Table I) of the above inhomogeneous materials, such as average trap distributions and attempt to escape frequencies, which are in agreement with those obtained by other techniques. [33][34][35] In addition, we have found that the MPC measurements of pentacene films are compatible with the fact that the majority carriers from an effective transport path interact via trapping and thermal release with broad trap distributions. 24 The notion of the effective transport path of the majority carriers deals with either transport in the delocalized states or transport by hopping.…”