D5 DLTS (Deep Level Transient Spectroscopy)

Topic

A filling pulse applied to this junction—the experimental method described by this model—temporarily fills deep-level states within the junction's depletion region with charge carriers. Upon the conclusion of the pulse, as the junction relaxes, a capacitance transient is produced: the deep-level states, having been filled with carriers, subsequently release them over time. This progressive emission of charge carriers causes the junction's capacitance—measured over that period—to relax from the value induced by the filling pulse back to the steady-state value it held beforehand. If these deep-level states release the carriers more rapidly following the pulse, the capacitance transient consequently relaxes more quickly toward that steady-state value.

By measuring this capacitance transient at various junction temperatures and applying an Arrhenius analysis to the relaxation rate at each temperature, one can determine the thermal emission rate at which the deep-level states release their carriers: at higher junction temperatures, the deep-level states release carriers more readily, and the capacitance transient consequently relaxes more rapidly toward its steady-state value. Thus, a higher junction temperature results in a higher thermal emission rate for these deep-level states, as indicated by the Arrhenius analysis. Thus, this model—utilizing the capacitance transient and thermal emission rate with which it began—derives both the activation energy and the capture cross-section of these deep levels (which are described in greater detail by another model in this set) from the Arrhenius plot generated by measuring the thermal emission rate at various junction temperatures: the slope of this Arrhenius plot reveals the activation energy—the energy a charge carrier trapped in one of these deep levels requires to be thermally re-emitted—while the y-intercept of the same plot reveals the capture cross-section, representing the ease with which one of these deep levels recaptures a free charge carrier. Consequently, if these deep levels exhibit a higher activation energy, the Arrhenius plot displays a steeper slope, and the thermal emission rate of these deep levels—at a given junction temperature—is correspondingly lower.

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