Abstract
A new diagnostic technique can be used to measure simultaneously the excess free-carrier lifetime τ and the diffusion length L with spatial resolution in semiconductor samples. The technique uses pulses of above-band-edge light to generate carriers near the sample surface. The carrier density evolution into the bulk is measured by means of the free-carrier absorption of an ir laser beam. Computer fitting the time variation of the absorption at any beam position to the carrier transport equation yields τ and L, enabling the diffusion coefficient D = L2/τ to be evaluated. Using 104-W/cm2 injection light and a 3.39-μm laser probe on a 1500-Ω cm silicon sample yielded bulk values in good agreement with calculated and independently measured values.
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