Relative sensitivity of photomodulated reflectance and photothermal infrared radiometry to thermal and carrier plasma waves in semiconductorsIt is shown that the new photothermal technique of lock-in rate-window infrared radiometry is capable of completely separating out photoexcited free-carrier-wave and thermal-wave contributions to the photothermal signal from an n-type, Cr-doped Si wafer with a simple experimental procedure, and with superior temporal resolution in the determination of the electronic lifetime and thermal transport time constant.
A new noncontact technique for the determination of excess carrier lifetimes in semiconductors is presented. The technique employs a square laser pulse (hv > Eg) and measures the infrared photothermal radiometric response of the sample. By applying the photothermal rate-window concept, the excess photoexcited carrier bulk lifetime was measured with optimal signal-to-noise (S/N) ratio and simple, unambiguous interpretation from the maximum position of the rate-window signal. The technique has been applied to Au-, Fe-, and Cr-doped Czochralski silicon crystals. The experimental results from boxcar and lock-in rate-window methods were found to agree very well. The results are further mostly in agreement with those from the noncontact laser/microwave detection method.
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