| Abstract |
Nonlinear drift conduction under a trap-density gradient is mathematically formulated. Semianalytical and numerical solutions demonstrate bulk-induced unidirectional current flow, i.e., rectification.... The present theory is in excellent agreement with various experimental J−V characteristics (J: current density and V: applied voltage). At low V, the J−V characteristics are ohmic and bidirectional. As the injection increases, the J−V characteristics become nonlinear and exhibit unidirectionality under proper conditions. The major requirements for a large unidirectionality are the trap-density gradient G⪢1, an intermediate V, and not too large trap-filling factor Θ, which requires the presence of acceptorlike traps. The unidirectional J−V characteristics due to the difference in trap-filled-to-trap-free-limit voltage V_TFL for forward and reverse bias markedly resemble the standard rectification. In addition, the trap-density gradient yields a positive T dependence of resistance for a proper set of parameters, evident J∝V^1.5 characteristics, and a photovoltaic effect. The present results suggest that bulk conduction under trap-density gradient explains fractions of resistance switching and rectification phenomena. The semianalytical solutions are verified by numerical solutions and comparison with experiments. In particular, semianalytical solutions for shallow-trap case excellently fit the experimental data by three parameters in practice: two scaling factors and G.show more
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PhysRevB_81_195210_2010