An Apparatus for IFTOF Measurements

If the material exhibits slow polarization currents during switching, then the bridge technique fails, unless one uses an identical sample for the nuUing capacitance and employs a resistance ratio bridge. 

Photoexcitation was achieved by using a triggerable nitrogen gas laser (LGI-21). The laser output pulse was of duration 8ns at a wavelength of 337nm. 

The IFTOF technique requires the current mode of operation in which the various Resistance-capacity product (RC) time constants in the bridge are much smaller than the transit time tj. If the resistance Ri is larger than Rj, then the signal across the amplifier will be simply Rj i(t), where i(t) is the transient photocurrent. 

In the current apparatus, the TOF signal was displayed on a 400-MHz analog oscilloscope. The waveform from the screen was coupled into an IBM personal computer for data analysis and storage. In general, TOF experiments are carried out under single-shot measurements, which means that the single-event bandwidth of the oscilloscope must be much larger than l/t-p. 

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