Abstract
The electronic transport in low-dimensional materials is controlled by quantum coherence and non-equilibrium statistics. The scope of the present investigation is to search for the origins of negative-differential resistance (NDR) behavior in N-doped ultra-narrow zigzag-edge ZnO nano-ribbons (ZnO-NRs). A state-of-the-art technique, based on a combination of density-functional theory (DFT) and non-equilibrium Green’s function (NEGF) formalism, is employed to probe the electronic and transport properties. The effect of location of N dopant, with respect to the NR edges, on IV-curve and NDR is tested and three different positions for N-atom are considered: (i) at the oxygen-rich edge; (ii) at the center; and (iii) at the Zn-rich edge. The results show that both resistance and top-to-valley current ratio (TVCR) reduce when N-atom is displaced from O-rich edge to center to Zn-rich edge, respectively. After an analysis based on the calculations of transmission coefficient versus bias, band structures, and charge-density plots of HOMO/LUMO states, one is able to draw a conclusion about the origins of NDR. The unpaired electron of N dopant is causing the curdling/localization of wave-function, which in turn causes strong back-scattering and suppression of conductive channels. These effects manifest themselves in the drawback of electric current (or so called NDR). The relevance of NDR for applications in nano-electronic devices (e.g., switches, rectifiers, amplifiers, gas sensing) is further discussed.
Highlights
Research on zinc oxide (ZnO) commenced as early as 19351, earlier than research on many semiconductors, only the recent few decades have witnessed several breakthroughs paving the way for revolutionary applications that exploit the multifunctional properties of ZnO and making it highly competitive in the market[2,3,4]
The present investigation focuses on ZnO nanoribbons (ZnO-NR) and their applications in nano-electronics, especially as N-doping is found to yield negative differential resistance (NDR) behavior at low bias
In the arena of gas-sensing applications, in our recent work[65], we reported that NDR in ZnO-NR:N can play a major role in inducing high selectivity toward detecting H2 molecules
Summary
Research on zinc oxide (ZnO) commenced as early as 19351, earlier than research on many semiconductors, only the recent few decades have witnessed several breakthroughs paving the way for revolutionary applications that exploit the multifunctional properties of ZnO and making it highly competitive in the market[2,3,4]. As a matter of fact, nanorods possess special characteristics completely different from the bulk ones[13] Such properties make them suitable for even broader range of applications for instance in: (a) nano-electronics: ZnO nanorods are utilized as extended gate in MOSFET14, and logical circuits[15]; (b) nano-photonics: ZnO nanorod arrays were used as photonic crystals[16], as light waveguide[17], as LED18, as radiation detector[19] and in dye-sensitized solar cells[20]; (c) biomedicine: ZnO nanorods and nanoparticles are utilized in biological and biomedical application (diagnosis and therapy) as to possess high radiative efficiency and least toxicity[21,22]; (d) Spintronics: Magnetic studies showed that Co-doped ZnO nanorods exhibited room-temperature ferromagnetism with a magnetization increasing with Co content[23]; (e) Gas-sensing: www.nature.com/scientificreports/. J.B (Ian) Gunn further discovered the Gunn’s effect in 1962, when he observed random noise-like oscillations, validated by the existence of NDR, after applying a bias on n-type GaAs samples and crossing a certain threshold[36]
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