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Modeling the low-voltage regime of organic diodes: Origin of the ideality factor
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Image of FIG. 1.
FIG. 1.

Energy diagram of an MIM diode. is the diffusion (or built-in) potential, which amounts to the difference between the work function of the anode and that of the cathode. is the potential applied to the anode, with the cathode being connected to ground. From left to right: reverse-biased, thermal-equilibrium, flat-band, and forward-biased condition. The arrows symbolize the various regimes of the diode. From left to right: reverse bias, injection-limited forward bias, and bulk-limited forward bias regime.

Image of FIG. 2.
FIG. 2.

Calculated potential profiles in a 200-nm-thick MIM diode with three values for the anode hole barrier: 0.1, 0.2, and 0.3 eV. The respective cathode barriers are 0.7, 0.8, and 0.9 eV.

Image of FIG. 3.
FIG. 3.

Calculated potential profiles in an MIM diode without and with a distribution of traps. The parameters used for the calculation are listed in Table I .

Image of FIG. 4.
FIG. 4.

Comparison between the simulated and analytical curves.

Image of FIG. 5.
FIG. 5.

Simulated curves with various doping concentrations in pentacene. This result points out that the assumption of zero doping is applicable as long as the dopant density lies below the injected carrier density at the anode.

Image of FIG. 6.
FIG. 6.

Effect of an exponential trap distribution on the potential profile as estimated by simulation with the same parameters as for the analytical model in Fig. 3 .

Image of FIG. 7.
FIG. 7.

Effect of an exponential distribution of traps on the characteristics of an organic diode. The traps result in a deviation of the forward current at low biases from the exponential growth, which can be interpreted in terms of an ideality factor. Ideality factor becomes higher with increasing .

Image of FIG. 8.
FIG. 8.

data in the bulk-limited regime (2 to 8 V) plotted in log-log scale together with the best-fit simulation and the prediction of Mark-Helfrich’s model (trap-limited SCLC).

Image of FIG. 9.
FIG. 9.

Measured curve of a pentacene diode. The inset shows the structure on a glass substrate. The Au bottom electrode serves as the injecting contact (anode), and the Al top electrode is the blocking contact (cathode). The active area of the device is 4 × 10−4 cm2. The best simulation is also shown.


Generic image for table
Table I.

Parameters used for the analytical calculations.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Modeling the low-voltage regime of organic diodes: Origin of the ideality factor