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Proceedings Paper

Time-dependent analysis of electron-wave directional couplers
Author(s): T. Singh; G. Qian; Marc M. Cahay
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Paper Abstract

Recently several proposals of quantum interference devices have appeared based on the close proximity of two coupled electron waveguides. The steady-state analysis of these new electron-wave directional couplers indicates that these devices are feasible using current fabrication technology, and could be used as basic switches in high-performance digital circuit at low enough temperature. In order to investigate the potential high-frequency applications of these newly proposed electron directional couplers, we have studied the transfer of wavepackets between parallel quantum wells using a block alternating direction implicit technique to solve the two dimensional time-dependent Schrodinger equation following the scalar ADI scheme of Douglas and Gunn. While injecting a wavepacket in one well, we show that only a partial transfer between wells (varying with incident kinetic energy) is reached even for perfectly symmetric double-quantum wells (in the direction of growth). This contrasts with the 100% probability of transfer predicted using the steady state coupled mode theory. The length and time scales for maximum transfer are found to be around a few thousand angstroms and in the sub-picosecond regime, respectively. In the presence of an external magnetic field Byields parallel to the interfaces of the double quantum well, the probability of transfer between wells can be partially reduced with a magnetic field of few Teslas. We also illustrate the more efficient possibility of tuning the probability of transfer between wells using an external gate voltage as proposed by Dagli et al. Finally, the presence of a small amount of impurities in the direction coupler is found to have a relatively small influence on the probability of transfer of electron wavepackets between wells as long as the Fermi energy is large compared to the strength of the impurity potential. The probability of transfer between waveguides also varies with the actual impurity configuration.

Paper Details

Date Published: 3 September 1992
PDF: 11 pages
Proc. SPIE 1675, Quantum Well and Superlattice Physics IV, (3 September 1992); doi: 10.1117/12.137592
Show Author Affiliations
T. Singh, Univ. of Cincinnati (United States)
G. Qian, Univ. of Cincinnati (United States)
Marc M. Cahay, Univ. of Cincinnati (United States)

Published in SPIE Proceedings Vol. 1675:
Quantum Well and Superlattice Physics IV
Gottfried H. Doehler; Emil S. Koteles, Editor(s)

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