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Charge carrier trapping states in thin evaporated and Langmuir-Blodgett organic films

✍ Scribed by I. Muzikante; E. Fonavs; E. A. Silinsh


Publisher
John Wiley and Sons
Year
1996
Tongue
English
Weight
380 KB
Volume
6
Category
Article
ISSN
1616-301X

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✦ Synopsis


Thermally modulated space-charge-limited current (TM-SCLC) and conventional SCLC methods have been used to determine the energy parameters of the local charge trapping states for three heterocyclic organic compounds in two different structural statesas thin vacuum-evaporated layers and Langmuir-Blodgett (LB) multilayer films. The TM-SCLC method provides higher resolution and accuracy of trap depth (Et) determination with error not greater than f 0.02 eV. In sandwich-type samples Melorganic IayerlMe of metal-free phthalocyanine (a-H,Pc), five sets of hole trapping states are determined in the energy range from 0.55 to 0.07 eV; for dimethylamino-benzylidene indandione-1,3 (DMABI) samples also, five sets of trapping states are detected in the 0.5-0.28 eV range; however, for indandione pyridinium betaine-l,3 (IPB) samples, only a very shallow set of traps at €, = kT emerged. In the case of evaporated layers the conductivity activation energy (En) dependence on voltage energy (U), En = €. ( U), decreases in a step-like manner, every step giving the trap depth Et of the corresponding set of trapping states. In the case of LB multilayers of vanadyl phthalocyanine (VOPc) and IPB films the En = €, ( U) dependences are of complex, oscillatorytype character, possibly caused by a spatially non-uniform trap distribution in the bulk of the sample.


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