TIME-RESOLVED AND ENERGY-RESOLVED EMISSION-SPECTROSCOPY USING A STEP-SCAN FT SPECTROMETER COMBINED WITH CORRELATIONAL ANALYSIS TECHNIQUES

decay of photoluminescence emission signals on the time scale from mic roseconds to seconds can be measured with superior dynamics and signal -to-noise ratio by a new method which makes use of correlation analysi s with pseudorandom binary sequences. Instead of excitation of the sam ple by one short laser pulse for each decay cycle (which results in lo w average emission intensity), the sample Is pumped with a continuous- wave laser modulated by a pseudorandom sequence with delta-function-li ke autocorrelation properties. Therefore, on the time average half of the exciting laser power pumps the sample, and the resulting high emis sion intensity allows recording of photoluminescence decays over as ma ny as four orders of magnitude within measurement times of 10 min. Whe n this technique is combined with a step-scan Fourier transform spectr ometer, both time and energy resolution can be obtained simultaneously , For each interferometer step, the sample response to the excitation sequence is recorded, later autocorrelated digitally, and combined to interferograms for each time step, and finally Fourier transformed, Wi th this technique, time-resolved high-sensitivity spectra can be recor ded in the NIR, where only detectors with relatively poor detectivity (D) are available, and in the visible spectral range. Preliminary res ults obtained from relatively slow emission processes at defects in se miconductors are presented, which show decay constants on microsecond to millisecond scales.