Control of surface recombination of Si wafers by an external electrode

A transparent electrode was placed close to a Si wafer, and a negative or positive voltage up to 2kV was applied to the electrode with respect to the wafer. The wafer was irradiated through the electrode with a pulsed laser, and the decay of the excess carriers was monitored by the microwave reflectance photoconductivity decay (mu-PCD) method. The carrier lifetime of p- and n-type as-polished wafers was increased by a factor of 3 by application of a 2 kV negative voltage to the electrode. This showed that the surface recombination velocity was controlled by the external electrode. A different tendency was observed for the oxidized wafers, and these results were explained by considering the surface charge and the surface state.