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  • The drift-diffusion interpretation of the electron current within the organic semiconductor characterized by the bulk single energy trap level
    Cvikl, Bruno
    The closed solution for the internal electric field and the total charge density derived in the drift-diffusion approximation for the model of a singlelayer organic semiconductor structure ... characterized by the bulk shallow single trap-charge energy level is presented. The solutions for two examples of electric field boundary conditions are tested on room temperature current density-voltage data of the electron conducting aluminumžtris(8-hydroxyquinoline aluminumžcalcium structure šW. Brütting et al., Synth. Met. 122, 99 (2001)đ for which jexpšproportionalđVa3.4, within theinterval of bias 0.4 V<=Va<=7. In each case investigated the apparent electron mobility determined at given bias is distributed within a given, finite interval of values. The bias dependence of the logarithm of their lowerlimit, i.e., their minimum values, is found to be in each case, to a goodapproximation, proportional to the square root of the applied electric field. On account of the bias dependence as incorporated in the minimum value of the apparent electron mobility the spatial distribution of the organic bulkelectric field as well as the total charge density turn out to be bias independent. The first case investigated is based on the boundary condition ofzero electric field at the electron injection interface. It is shown that for minimum valued apparent mobilities, the strong but finite accumulation of electrons close to the anode is obtained, which characterize the inverted space charge limited current (SCLC) effect. The second example refers to the internal electric field allowing for self-adjustment of its boundary values. The total electron charge density is than found typically to be of U shape, which may, depending on the parameters, peak at both or at either Alq3 boundary. It is this example in which the proper SCLC effect is consequently predicted. In each of the above two cases, the calculations predict the minimum values of the electron apparent mobility, which substantially exceed the corresponding published measurements. For this reason the effect of the drift term alone is additionally investigated. On the basis of the published empirical electron mobilities and the diffusion term revoked, it is shown thatthe steady state electron current density within the AlžAlq3 (97 nm)žCa single layer organic structure may well be pictured within the drift-only interpretation of the charge carriers within the Alq3 organic characterized bythe single (shallow) trap energy level. In order to arrive at this result, it is necessary that the nonzero electric field, calculated to exist at the electron injecting Alq3žCa boundary, is to be appropriately accounted for in the computation
    Source: Journal of applied physics. - ISSN 0021-8979 (Iss. 2, Vol. 107, 2010, str. 023710-1-023710-9)
    Type of material - article, component part
    Publish date - 2010
    Language - english
    COBISS.SI-ID - 23363879

source: Journal of applied physics. - ISSN 0021-8979 (Iss. 2, Vol. 107, 2010, str. 023710-1-023710-9)
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