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Rectifying behavior realized without p-n junction


By
Wenzhe Guo

June 26, 2017 - Posted in Discussion
Rectifier is used to convert the alternating current (AC) to direct current (DC), due to rectifying behavior that current increases sharply in the condition of forward bias, whereas little current flows in the reverse bias, as shown in Figure 1[1]. At present, solid-state electronic devices with rectifying behavior are mostly achieved by the incorporation of conventional p-n junction that requires doping technology. However, without doping technology to form p-n diode, the rectifying behavior still could come out of electronic devices, like magnetic tunnel junction, molecule diode.

WZ1.jpg
Figure 1. Current-voltage characteristics of rectifier

Magnetic tunnel junction (MTJ):
MTJ is formed with a barrier like thin insulator functionalized by magnetoresistive effect sandwiched by two ferromagnet conducting layers, where electrons could travel through one ferromagnet into the other by quantum tunnel process. H. Cheng and his coworkers proposed the realization of a tunnel diode based on magnetic tunnel junction Ag/MgO/SrRuO3, which shows good rectifying performance in a wide bias range [2].
Molecule diode:
A single-molecule rectifier was proposed consisting of a molecule attached to two conductive electrodes composed of a π-donor and π-acceptor moiety separated by an σ-bonded bridge, shown in Figure 2a[3]. Under an applied bias, the molecule is far from equilibrium conditions, potentially resulting in significant electronic and structural reconfiguration. To realize rectification, one approach could be by controlling the non-symmetry of the molecule. The rectifying behavior is caused by a molecule structure where the energy levels of the molecule within different sections of the molecule are affected variously by a bias, resulting in a higher current density in one direction. Figure 2b and c show the energy band diagram of a device with non-symmetric contacts in positive and negative bias conditions, respectively.

WZ2.jpgFigure 2. Energy-band diagram of molecule diode. a) Aviram-Ratner configuration, b) Positive and c) negative bias conditions.

Reference
[1] Rectifier, Wikipedia. https://en.wikipedia.org/wiki/Rectifier
[2] H. Cheng, et al., Rectifying behavior of Ag/MgO/SrRuO3 tunnel junction: First principles modeling of tunnel diode, IEEE, 2012.
[3] D. Jane. Molecular electronics: Rectifying current behaviours, Nature Chemistry 1, 2009: 601 - 603.
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