Bulk carrier lifetime measurement by the microwave reflectance photoconductivity decay method with external surface electric field

We attempted to measure the bulk carrier recombination lifetime of Si wafers by the microwave reflectance photoconductivity decay (PCD) method. Voltage was applied between an external electrode and a Si wafer to suppress surface recombination. Before the measurement, the surface state density was reduced by a chemical treatment using NH4OH–H2O2–H2O and diluted HF solutions. Carrier lifetime as long as 1 ms was measured by the present method for a wafer with a bare surface. Comparison with results for oxidized wafers show that the present method can suppress surface recombination more effectively than thermal oxidation, which has been often used for surface passivation in PCD measurements.