Investigation of defect formation and electronic transport in microcrystalline silicon deposited by hot-wire CVD

We have investigated doped and undoped layers of microcrystalline silicon p repared by hot-wire chemical vapour deposition optically, electrically and by means of transmission electron microscopy. Besides needle-like 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 o xygen content of several per cent in the porous phase was detected by elect ron energy loss spectrometry. Deep-level transient spectroscopy of the crys tals 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 perpe ndicular 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 por ous phase is believed to be an important loss mechanism in the output of a pin-structured photovoltaic solar cell deposited by hot-wire CVD. (C) 1999 Elsevier Science B.V. All rights reserved.