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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.

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.

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