Influence of pulse thermal annealing on photoelectrical properties of locally grown polycrystalline silicon films

Abstract

It is known that electroforming of the polycrystalline silicon films (PSF) by current pulses gives rise to the memory effects of anomalous photovoltage (APV) and negative capacitance [1][2][3]. In this case the I-V characteristics (IVC) of PSF, almost symmetrical in respect to the polarity of the applied voltage, become diode-like after the electroforming.The mechanism of asymmetry induction in IVC of PSF, suggested in [4], assumes that a thermal breakdown in the current direction occurs in one of the two barrier layers at the opposite grain boundaries, namely, in the one which at a given polarity of the forming voltage is under a reverse bias.The APV effect in PSF is of interest from the viewpoint of design of planar solar cells not requiring additional p-n junctions and having a high conversion factor.However, electroforming of each separate cell by current pulses is time-consuming and is not efficient for mass production.In this work, we studied the possibility of PSF formation by pulse thermal annealing (PTA) with the help of IR radiation using the ITO-18MV system described in [5].The PSF under study were grown together with ntype epitaxial films (thickness 5 µm, concentration of phosphorus dopants 10 15 cm -3 ) on locally masked substrate KDB-10 (boron-doped silicon, 10 Ohm cm) using the technology described in [6]. Samples were the resistors of rectangular shape with linear dimensions 400×40 µm 2 and contact area 100×100 µm 2 . The contact regions were additionally doped by diffusion of phosphorus atoms in order to create Ohmic contacts.