A correlation method for semiconductor transient signal measurements

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Abstract
A wide variety of experiments in semiconductor physics involve the observation of a particular class of time-dependent transient signals; namely, decaying exponentials. Such signals are characteristic of systems relaxing back to equilibrium following an abrupt change in the populations of carriers occupying the available states. The magnitudes of such signals indicate the density of states involved, while the decay time constants (as a function of temperature) provide information on the energy level of the states in question. As such, both the amplitudes and the time constants of such signals are of physical interest. The problem of processing such signals has been examined using the theory of linear filtering and as a result a special purpose signal processor has been developed. This processor performs a continuous real-time cross correlation between the experimental signals and an appropriately synchronized locally generated exponential waveform. The resulting system has been used to process signals from transient space-charge measurements on reverse-biased gold-doped silicon junction diodes, providing both correlation spectra that yield energy levels and also trap profiles that expose the spatial distribution of the gold inside the junctions.