Silicon surface passivation by Al2O3: Recombination parameters and inversion layer solar cells

The interface between p- and n-type FZ-Si and an amorphous aluminum oxide (Al2O3) surface passivation layer deposited by plasma-assisted atomic layer deposition (ALD) was investigated by frequency-dependent conductance measurements. The hole capture cross section in the lower half of the bandgap, sigma(p) = (4 +/- 3)x10(-16) cm(2), was found to be independent of energy. The electron capture cross section n in the upper half of the bandgap decreases from sigma(n) = (7 +/- 4)x10(-15) cm(2) at midgap over two orders of magnitude towards the conduction band edge. Numerical simulations of the effective surface recombination velocity based on these recombination parameters show a good agreement with experimental surface recombination velocities for a wide range of excess carrier and surface charge densities. Carrier transport in the inversion layer formed at the n-Si/Al2O3 interface was investigated yielding a sheet resistance of 15 k Omega/square, which was reduced to 6 k Omega/square for a surface charge density of -2x10(13) cm(-2) obtained by corona charging. The applicability of Al2O3 inversion layers as emitters in n-type inversion layer solar cells was demonstrated by short circuit current densities of up to 25 mA/cm(2), which show a pronounced dependence on surface charge density. (C) 2012 Published by Elsevier Ltd. Selection and peer-review under responsibility of the scientific committee of the SiliconPV 2012 conference.