Trap Recharging Mechanism

But at the same time the mobility was redueed by about one order of magnitude by the purifieation. Reduetion of the hysteresis does not neeessarily mean that impurity indueed traps must be eausal for the hysteresis. The relative stability of polarons and bipolarons depend also on the presenee of impurities and ean be modified in this manner. Also for the eapaeitor with pentaeene, prepared from a soluble preeursor, the hysteresis is rather small. For sueh small moleeules one ean rule out a bipolaron meehanism, and apparently neither traps nor mobile ions lead to hysteresis. 

As aheady mentioned, trap reeharging alone ean in prineiple lead to hysteresis [10]. But the shape of the simulated CV eurves deviated signifieantly from the observed ones. The meehanism of trap reeharging will be analysed ftirther below in Seetion 16.4. In Seetion 16.6 proeesses will be eonsidered in whieh doubly eharged states on the polymer ehains are involved. But first the equilibrium will by newly analysed. 

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Numerical simulations on the trap recharging mechanism in MIS capacitors and transistors indicate that energetically distributed traps in particular can lead to hysteresis in these devices. On the other hand, the form of the simulated hysteresis deviates from the observed one and extreme parameter values are needed either for the total trap concentration or for the product from capture cross section and thermal velocity. We conclude that it is more likely that trap recharging can modify a hysteresis caused by another mechanism than being the main origin of the hysteresis. 

In Section 16.4 we come back to hysteresis effects by trap recharging. We have shown in Ref [10] that this mechanism can lead to hysteresis in quasistatic CF-curves of organic MIS capacitors. However, the form of the curves was qualitatively different from the observed ones. This analysis is extended... 

Several mechanisms for the hysteresis effeets have been proposed in the literature, in most cases as verbal statements without mathematical formulation and numerical evaluation. Typical statements are that trap recharging or mobile ions are likely to cause the hysteresis. Additionally we have proposed that formation and dissociation of bipolarons in the accumulation layer can cause this effeet. 

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