Single-Electron Transport in Colloidal Quantum Dots of Narrow-Gap Semiconductors
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-Electron Transport in Colloidal Quantum Dots of Narrow-Gap Semiconductors N. D. Zhukova*, M. V. Gavrikovb, and D. V. Kryl’skiic a NPP
Volga LLC, Saratov, 410033 Russia Saratov State University, Saratov, 410012 Russia c Research Institute of Applied Acoustics, Dubna, Moscow oblast, 141981 Russia *e-mail: [email protected] b
Received April 24, 2019; revised June 6, 2020; accepted June 7, 2020
Abstract—Single-electron transport in a planar structure of InSb, PbS, and CdSe semiconductor colloidal quantum dots has been studied by scanning tunneling microscopy. Current dips similar to the Coulomb gap have been observed in the I–V characteristics. The qualitative and numerical comparative estimates suggest that a structure consisting of a set of quantum dots exhibits single-electron transport and a phenomenon similar to the Coulomb blockade. The white light illumination of the sample during the measurements of the I–V characteristics breaks the Coulomb blockade and one can expect that a device element based on such a structure will respond to individual photons. In the Coulomb gap region, current oscillations at terahertz frequencies can occur. Keywords: colloidal quantum dot, single-electron transport, electron emission, Coulomb blockade, Coulomb gap. DOI: 10.1134/S106378502009014X
Single electronics is a promising field of microand nanoelectronics [1, 2]. In this direction, the main phenomenon under study is single-electron transport, which represents a sequential electron–electron tunnel hopping through a quantum-dimensional structure, e.g., a quantum dot (QD), or the electron flight in it with a certain time delay. In the latter case, under certain conditions, the next flying electron can be blocked by the previous one, which is called the “Coulomb blockade.” In this case, a dip (current instability) region is formed in the I–V characteristic, which is referred to as a “Coulomb gap” in the literature. In QDs, the quantum states of an electron occur due to its resonant motion (the standing wave function) under size limitation conditions in certain directions of the wave vector (Brillouin) zone. In this case, the QD size should be smaller than electron de Broglie wavelength Λ = h(2mE)–1/2 (h is the Planck’s constant, m is the electron effective mass, and E is the electron kinetic energy). Under these conditions, the Coulomb selection of real electronic states is implemented when a QD contains one or several (conditionally free) conduction electrons. In metal nanoparticles, these conditions are met by freezing at temperatures up to that of liquid helium [1]. In semiconductor QDs, the processes can be observed at high temperatures due to the extreme smallness of the intrinsic conduction electron density and volume.
In practice, the main investigations of single-electron transport in semiconductors are carried out on quantum-dimensional structures of silicon as the basic material of microelectronics [2, 3]. However, for the phenomena discussed here, silicon cannot be preferred because of the extreme smallness (~1 nm)
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