Lifetime measurements on silicon-on-insulator wafers

We report noncontact measurements of the effective minority carrier lifetime in the superficial silicon layer of silicon-on-insulator wafers. The carriers are excited by a pulse of short-wavelength photons (λ≤350 nm), all of which are absorbed in the first 500 Å of the silicon layer. The carriers are detected by the change in microwave reflectance in a resonant circuit to which the wafer is coupled. The results obtained vary from ∼3 μs for a three year old separation by implanted oxygen (SIMOX) wafer to ∼25 μs for current vendor SIMOX and bond-etchback samples. The variation in free surface recombination velocity is eliminated by HF passivating the samples prior to measurement.