Analytical Estimation of Effective Lifetimes of Minority Carriers Injected with Laser Pulse into Dry-Oxidized p-Type Silicon Wafer

Effective lifetimes measured with the microwave-detected photoconductive decay method are often unexpectedly short compared with those obtained with the conventional photoconductive decay method, particularly when photocarriers stored in space-charge layers at the surfaces of specimen wafers are negligible compared with those remaining in the specimen volume. On numerically resolving the continuity equation for excess photocarriers, it has been found that the short effective lifetimes are caused mainly by the surface electric fields of the specimens and partly by the relatively short wavelength (905 nm) of the photocarrier-generating laser beam. The comparatively short pulse width (150 ns) of the beam must also be a cause.