| Apr 10, 2020 |
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(Nanowerk News) Single electron pumping devices with high efficiency and controllability at room temperature play an essential role in implement spin-based quantum computing and quantum information processing.
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In a recent study, which was published in Science China Physics, Mechanics & Astronomy (“Single-electron pumping in a ZnO single-nanobelt quantum dot transistor”), single-electron transistors (SETs) based on single indium-doped ZnO nanobelt (NB) were built by Xiulai Xu, et al., scientists at the Institute of Physics, Chinese Academy of Sciences.
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Clear Coulomb oscillations in the SETs were observed at 4.2 K. Single- and double-electron pumping was also achieved by using a back-gated AC signal for different pumping voltages.
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| Conductance oscillations in the ZnO NB SET at 4.2 K: (a) with uniform Coulomb gap; (b) with non-uniform Coulomb gap; contour plots of differential trans-conductance at 4.2 K; (c) for single-tunneling quantum dots; (d) for multi-tunneling junctions. (© Science China Press) (click on image to enlarge)
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Diluted magnetic semiconductors (DMSs), which possess both magnetic and semiconductor properties, was found that the magnetic properties in host materials could be formed by introducing small portions of magnetic materials and that their optoelectronic transport properties did not concurrently degrade.
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The researchers stated: “Many DMSs, such as indium-doped Mn5Ge3 and (Ga, Mn)As, have been used for precise spin injection and detection purposes. However, the low Curie temperatures, caused by narrow bandgap, limit their application at room temperature. Therefore, wide bandgap semiconductor materials such as ZnO doped with transition metals are highly desirable.”
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The doping of transition metals in ZnO can improve its ferromagnetic properties, which are advantageous for future applications in spintronics. Among these ZnO materials, they pointed out, “ZnO nanobelts (NBs) are attractive candidates for optoelectronic and nanoscale electronic applications because of the direct wide bandgap (3.37 eV), high exciton binding energy at room temperature (60 meV), and large surface-to-volume ratio.”
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Being highly charge sensitive, single-electron transistors (SETs) are ideal for studying quantum effects such as Coulomb blockade, tunneling, and single-electron pumping and have shown vast applications in charge detection, thermometry, single-spin detection, single-photon detection, and so on.
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According to the researchers, single-electron tunneling-based devices such as SETs and single-electron pumps have been investigated using metal, semiconducting materials, and DMSs [(Ga, Mn)As-based SETs] for spin storage and single-electron charging.
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However, only a few studies on ZnO NB SETs have been conducted, and there has been no research into the advantages for single-electron spin control of single-electron pumping in ZnO quantum dots.
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| Single- and double-electron pumping in ZnO quantum dot: (a) for pump voltage of 3 V and (c) for pump voltage of 2.7 V, respectively. Pumping current as a function of pulse frequency for various bias voltage: for pump voltages of (b) 3 V and (d) 2.7 V. (© Science China Press) (click on image to enlarge)
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In the study, SETs based on single indium-doped ZnO NB were built. Strong Coulomb oscillations were observed at 4.2 K. “Periodic and non-periodic Coulomb diamonds observed were attributed to the presence of single uniform quantum dots and multi-quantum dots, respectively. The charging energy values were 4 and 5 meV in the case of the single and multi-dots systems, respectively, and the corresponding diameters of the quantum dots were approximately 86 and 70 nm,” they explained.
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Single- and double-electron pumping was also achieved by using a back-gated AC signal for different pumping voltages. The realization of controlled single- and double-electron pumping in ZnO quantum dots with the simplest configuration was a significant step toward understanding the coherent properties of electron spin in quantum dots for future applications.
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The results indicate that ZnO NBs are promising candidates for single-electron spin detection, which is useful for quantum computing and quantum information. Furthermore, the simple configuration of the device used in the study will make it more compatible with standard Si technology in the future.
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