In this paper we present new results on doped c-Si:H thin films deposited by Hot-Wire Chemical Vapour Deposition (HWCVD) in the very low temperature range (125-275 ºC). The doped layers were obtained by the addition of diborane or phosphine in the gas phase during deposition. The incorporation of boron and phosphorus in the films and their influence on the crystalline fraction are studied by Secondary Ion Mass Spectrometry and Raman Spectroscopy respectively. Good electrical transport properties were obtained in this deposition regime, with best dark conductivities of 2.6 S/cm and 9.8 S/cm for the p-and n-doped films respectively. The effect of the hydrogen dilution and the layer thickness on the electrical properties are also studied. Some technological conclusions referred to cross contamination could be deduced from the nominally undoped samples obtained in the same chamber after p-and n-type heavily doped layers.

Abstract:We have investigated doped and undoped layers of microcrystalline silicon prepared by hot wire chemical vapour deposition optically, electrically and by means of transmission electron microscopy. Beside needlelike crystals grown perpendicular to the substrate's surface all of the layers contained a noncrystalline phase with a volume fraction between 4% and 25%. A high oxygen content of several per cent in the porous phase was detected by electron energy loss spectrometry. Deep level transient spectroscopy of the crystals suggests that the concentration of electrically active defects is less than 1% of the undoped background concentration of typically 10 17 cm -3 . Frequency dependent measurements of the conductance and capacitance perpendicular to the substrate surface showed that a hopping process takes place within the noncrystalline phase parallel to the conduction in the crystals. The parasitic contribution to the electrical circuit arising from the porous phase is believed to be an important loss mechanism in the output of a pin-structured photovoltaic solar cell deposited by hot wire CVD.

Polysilicon Thin Film Transistors (TFT) are of great interest in the field of large area microelectronics, especially because of their application as active elements in Flat Panel Displays. Different deposition techniques are in tough competition with the objective to obtain device-quality polysilicon thin films at low temperature. In this paper we present the preliminary results obtained with the fabrication of TFT deposited by Hot Wire Chemical Vapor Deposition (HWCVD). Some results concerned with the structural characterization of the material and electrical performance of the device are presented.

Hydrogenated microcrystalline silicon films obtained at low temperature (150ºC-280ºC) by hot-wire chemical vapour deposition at two different process pressures were measured by Raman spectroscopy, X-ray diffraction spectroscopy and photothermal deflection spectroscopy.A high crystalline fraction (> 90%) with a low subgap optical absortion (10 cm -1 at 0.8 eV) were obtained in films deposited at high growth rates (>0.8 nm/s). These films were incorporated in nchannel thin film transistors and their electrical properties were measured. The saturation mobility found was 0.72  0.05 cm 2 /V·s and the threshold voltage around 0.2 eV. The dependence of their conductance activation energies on gate voltages were related to the properties of the material.

Abstract:Work function measurements on cross sectioned microcrystalline pin silicon solar cells deposited by Hot−Wire CVD are presented. The experiment is realized by combining a modified Kelvin probe experiment and a scanning force microscope. The measured surface potential revealed that the built−in electric drift field is weak in the middle of the compensated intrinsic layer. A graded donor distribution and a constant boron compensation have to be assumed within the intrinsic layer in order to obtain coincidence of the measurements and simulations. The microcrystalline p−silicon layer and the n−type transparent conducting oxide form a reverse polarized diode in series with the pin diode.