Phys. Rev. Applied 14, 044037 (2020) - Ultrafast Strain-Induced Charge Transport in Semiconductor Superlattices

Ultrafast Strain-Induced Charge Transport in Semiconductor Superlattices

F. Wang, C.L. Poyser, M.T. Greenaway, A.V. Akimov, R.P. Campion, A.J. Kent, T.M. Fromhold, and A.G. Balanov

Phys. Rev. Applied 14, 044037 – Published 20 October 2020

Abstract

We investigate the effect of hypersonic ( $> 1$ -GHz) acoustic phonon wave packets on electron transport in a semiconductor superlattice. Our quantum-mechanical simulations demonstrate that a gigahertz train of picosecond deformation-strain pulses propagating through a superlattice can generate current oscillations the frequency of which is many times higher than that of the strain pulse train, potentially reaching the terahertz regime. The shape and polarity of the calculated current pulses agree well with experimentally measured electric signals. The calculations also explain and accurately reproduce the measured variation of the induced-current-pulse magnitude with the strain-pulse amplitude and applied bias voltage. Our results open a route to developing acoustically driven semiconductor superlattices as sources of millimeter and submillimeter electromagnetic waves.

Received 27 March 2020
Revised 25 August 2020
Accepted 31 August 2020

DOI:https://doi.org/10.1103/PhysRevApplied.14.044037

Physics Subject Headings (PhySH)

Acoustic phonons Optoelectronics Quantum transport Strain

III-V semiconductors Superlattices

Schroedinger equation Terahertz techniques

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

F. Wang^1,2,*, C.L. Poyser², M.T. Greenaway ¹, A.V. Akimov ², R.P. Campion², A.J. Kent², T.M. Fromhold², and A.G. Balanov ¹

¹Department of Physics, Loughborough University, Loughborough LE11 3TU, United Kingdom
²School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom

^*f.wang@nottingham.ac.uk

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Vol. 14, Iss. 4 — October 2020

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Figure 1
(a) A schematic diagram of our device, which includes (toward the right) the weakly coupled SL, contacts and spacer layers. The optoelastic $Al$ film transducer (left) is deposited on the side of the $Ga As$ substrate opposite to the device. (b) The current-voltage characteristics, $I_{0} (V_{0})$ , of the device calculated numerically (open circles), approximated by a cubic polynomial (crosses) and measured experimentally (solid curve); the inset shows the numerically simulated time realization of strain pulses with a frequency of 46 GHz generated by the $Al$ film transducer, where $ϵ_{a}$ is the maximum strain within the train of pulses.
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Figure 2
(a)–(c) The time-dependent incremental current $δ I (t)$ calculated for $V_{0} =$ (a) $- 100 mV$ , (b) 0 mV, and (c) 100 mV, taking $ϵ_{a} = 1.5 \times 10^{- 4}$ . The gray curves show the signal and the colored curves are calculated using the moving-average method with a 12.5-GHz cutoff frequency. (d) The Fourier spectra $S$ of the (gray) signals in (a)–(c). The colors of the Fourier spectra correspond to those of the respective averaged signals in (a), (b), and (c). (e) Color maps: the evolution of the probability density ( $yellow = high$ ) of the acoustically driven electron wave packet calculated for $V_{0} = - 100$ mV, as in (a), shown enlarged in the lower right inset. The black curves show the averaged electron trajectory $⟨ x ⟩ (t)$ , revealing the drift and superimposed oscillations (inset) also seen in the wave-packet dynamics.
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Figure 3
Typical current pulses $δ I (t)$ calculated numerically (open circles, right axis) and experimentally measured (solid curves, left axis) for $V_{0} = + 100$ mV (red), $- 100 mV$ (green), and 0 (blue), $ϵ_{a} = 1.5 \times 10^{- 4}$ .
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Figure 4
The calculated (symbols, right axis) and measured (solid lines, left axis) variation of the current-pulse amplitude $δ I_{a}$ with applied bias $V_{0}$ (a) and strain-pulse amplitude $ϵ_{a}$ in the train (b). The open circles are the numerical calculations. The crosses are the values [divided by a factor of 20 in (a), and of $- 20$ in (b)] calculated from an analytical model developed to describe the response of the SL to irradiation by an electromagnetic wave [see the Appendix and Eq. (A2)].
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Figure 5
(a) The Fourier spectra, $S$ , of the $δ I (t)$ oscillations calculated for the SL with a monolayer barrier when $V_{0} = + 100$ mV (red), $- 100 mV$ (green), and 0 (blue), taking $ϵ_{a} = 1.5 \times 10^{- 4}$ . (b) The color map of the frequency up-conversion factor, $β$ , calculated as a function of the SL barrier width, $b$ , and period, $d$ . The value of $β$ is independent from $V_{0}$ . The black asterisk corresponds to the SL parameters in (a) and the yellow asterisk to those of the original SL considered earlier in the paper.
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Physical Review Applied

Ultrafast Strain-Induced Charge Transport in Semiconductor Superlattices

F. Wang, C.L. Poyser, M.T. Greenaway, A.V. Akimov, R.P. Campion, A.J. Kent, T.M. Fromhold, and A.G. Balanov

Phys. Rev. Applied 14, 044037 – Published 20 October 2020

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