Energetically distributed trapping states

In principle the situation seems to be similar for energetically distributed traps with Gaussian or exponential density of states. But especially in the case of an exponential trap density of states in the gap with the maximum at a distance Eq above the valence band edge... 

In Fig. 2.7, the TSDC observed in As Sei- for As content 8-15 at.% was shown. A peak at 210K dominates in the depolarization curve. In addition, a peak at 244 K and a shoulder at 197 K are discemable. Release of carriers from shallow states and subsequent trapping on relatively deeper ones transform the TSDC into curves 3 and 4 (Fig. 2.7). Activation energy determined for peaks with 210K and 244K is iit2 = 0.35 eV and Fts = 0.45 eV, respectively. These states are energetically distributed A t2 = 0.05 eV and AFto = 0.1 eV, respectively. 

The energetic distribution and activity of such trap states is not known, and will be a function of film composition and morphology and chemical environment. 

Figure 15. Energetics of the charge recombination following electron injection (/ i) from a dye excited state S into the conduction band of a semiconductor. Thermalization and/or trapping of injected electrons (Mh) takes place prior to the interfacial electron back transfer to the dye oxidized state S (/cb). The reaction free energy associated to the latter process depends upon the population of the electronic states in the solid and can be distributed over a broad range of values. Numerical potential data shown are those of the c/s-[Ru (dcbpy)2(NCS)2] Ti02 system.

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