Space-charge-limited conductivity

The results of several studies were interpreted by the Poole-Erenkel mechanism of field-assisted release of electrons from traps in the bulk of the oxide. In other studies, the Schottky mechanism of electron flow controlled by a thermionic emission over a field-lowered barrier at the counter electrode oxide interface was used to explain the conduction process. Some results suggested a space charge-limited conduction mechanism operates. The general lack of agreement between the results of various studies has been summari2ed (57). 

Wolf U, Barth S, Bassler H (1999) Electrode versus space-charge-limited conduction in organic light-emitting diodes. Appl Phys Lett 75 2035... 

A.J. Campbell, D.D.C. Bradley, D.G. Lidzey, Space-charge limited conduction with traps in poly(phenylene vinylene) light emitting diodes, J. Appl. Phys. 82 (1997) 6326-6342 ... 

Impurities which act as traps for charge carriers can be detected from the space-charge limited conductivity or from measurements of charge-carrier mobUity in favourable cases, and their concentrations can be determined, but not their identities (see Sect. 8.5.5). 

J. S. Bonham and D. H. Jarvis, A new approach to space- charge-limited conduction theory, Aust. J. Chem., 1977, 30, 705 J. S. Bonham and D. H. Jarvis, Theory of space-charge-limit current with one blocking electrode, Aust. J. Chem., 1978, 31, 2103 J. S. Bonham, Space-charge-limited current theory for a spatially non-uniform trap distribution, Aust. J. Chem., 1978, 57,2117. 

Important electrical informations about OLEDs, such as charge transport, charge injection, carrier mobility, etc., can be obtained from bias-dependent impedance spectroscopy, which in turn provides insight into the operating mechanisms of the OLED [14,15,73,75 78]. Campbell et al. reported electrical measurements of a PLED with a 50-nm-thick emissive layer [75], Marai et al. studied electrical measurement of capacitance-voltage and impedance frequency of ITO/l,4-Mv-(9-anthrylvinyl)-benzene/Al OLED under different bias voltage conditions [76], They found that the current is space-charge limited with traps and the conductivity exhibits power-law frequency dependence. 

The equation which describes the conduction for space charge-limited current in the case of a trap-free solid [32,120] is the Mott-Gurney equation [121]... 

S.C. Jain, W. Geens, A. Mehra, V. Kumar, T. Aernouts, J. Poortmans, R. Mertens, Injection- and space charge limited-currents in doped conducting organic materials,. /. Appl. Phys. 89 (2001) 3804-3810. 

Almost by definition, an electronic device has at least two contacts. Here we consider a single one therefore, it is assumed that the bulk conductivity of the material and the distance between contacts are large enough, so that over most of that distance the material s energy levels are not influenced by the contacts. This is not true in the case of space-charge-limited currents [215], especially in double injection, a situation that may occur in CP LEDs (see Section V.C). 

Fig. 6.31. Conductivity data for a p -p-p device. A is the annealed state, B is after a current has flowed for 24 hours, and P is after prolonged illumination. The reduction in space charge limited current is attributed to defect formation (Kruhler et at. 1984).

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