Measurement of coherent tunneling between InGaAs quantum wells and InAs quantum dots using photoluminescence spectroscopy

Yu. I. Mazur, V. G. Dorogan, D. Guzun, E. Marega, Jr., G. J. Salamo, G. G. Tarasov, A. O. Govorov, P. Vasa, and C. Lienau

Phys. Rev. B 82, 155413 – Published 8 October 2010

Abstract

We present a spectroscopic manifestation of the intermediate coherent tunneling regime between a quantum-dot (QD) and a quantum-well (QW) layer. We observe a nontrivial dependence of the resonant QD photoluminescence excitation (PLE) signal as a function of dot-well barrier thickness. For thick barriers and resonant QW excitation, the photogenerated QD carrier density increases exponentially with increasing coupling strength. For separations of a few nanometers only, however, we observe an anomalous decrease in the PLE signal. This behavior is defined by subpicosecond resonant coherent tunneling dynamics between the QW and QD. Our results shed light on the intermediate coherent tunneling regime of relevance in a variety of functional nanostructures such as charge or spin injectors or photovoltaic devices.

Received 31 July 2010

DOI:https://doi.org/10.1103/PhysRevB.82.155413

Authors & Affiliations

Yu. I. Mazur^*, V. G. Dorogan, D. Guzun, E. Marega, Jr.^†, and G. J. Salamo

Department of Physics, University of Arkansas, 226 Physics Building, Fayetteville, Arkansas 72701, USA

G. G. Tarasov

Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, pr. Nauki 45, Kiev-03028, Ukraine

A. O. Govorov

Department of Physics and Astronomy, Ohio University, Athens, Ohio 45701, USA

P. Vasa and C. Lienau

Institut für Physik, Carl von Ossietzky Universität, 26111 Oldenburg, Germany

^*ymazur@uark.edu
^†On leave from Instituto de Física de São Carlos, USP, São Carlos 13560-970, SP, Brazil.

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Vol. 82, Iss. 15 — 15 October 2010

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Images

Figure 1
(Color online) (a) Schematic presentation of the hybrid ${In}_{0.13} {Ga}_{0.87} As$ QW/InAs QD structure; (b) energy scheme of the structure and transitions under investigation. Relaxation processes are shown as wavy arrows; optical transitions are depicted by straight arrows. The QW and QD density of states are shown by shadowed areas; PL (solid lines) and PLE spectra (open circles) measured in the hybrid InAs QDs/ ${In}_{0.13} {Ga}_{0.87} As$ QW nanostructures with (c) $d_{b} = 11 nm$ and (d) $d_{b} = 2 nm$ at different excitation intensities at $T = 10 K$ . The spectra are shifted vertically for clarity, $I_{0} = 1000 W / {cm}^{2}$ .Reuse & Permissions
Figure 2
(Color online) (a) Low-temperature $(T = 10 K)$ PL and PLE spectra measured at different excitation intensities in a reference sample containing only an InAs QD layer. The spectra are shifted vertically for clarity. $I_{0} = 1000 W / {cm}^{2}$ . (b) PLE spectra measured in the hybrid ${In}_{0.13} {Ga}_{0.87} As$ QW/InAs QD structure with $d_{b} = 15 nm$ for an excitation intensity of $1.5 \times 10^{- 6} I_{0}$ . The spectra are recorded detecting the QD ground-state emission ( $E_{d e t} = 1.148 eV$ , open circles) and QW exciton emission ( $E_{d e t} = 1.348 eV$ , open squares), respectively. The QW PL spectrum (solid line) has been recorded at an excitation intensity of $5 \times 10^{- 6} I_{0}$ .Reuse & Permissions
Figure 3
(a) QD PLE signal under resonant excitation of the QW versus barrier transmission $T$ calculated for the GaAs barrier thicknesses $d_{b}$ shown in the top abscissa. The ratio of the maximum QW and QD PL intensity is shown for nonresonant excitation $(λ_{e x c} = 532 nm)$ at two different excitation intensities of $50 W / {cm}^{2}$ (open circles) and $0.15 W / {cm}^{2}$ (closed circles); (b) the same dependencies as in Fig. 3a measured for composite GaAs barrier including AlAs layer with different thicknesses.Reuse & Permissions
Figure 4
(Color online) (a) Normalized QD PLE signal under resonant excitation of the QW versus GaAs barrier thickness $d_{b}$ (bottom abscissa). The results from the Bloch equation model (solid line) are as a function logarithm of the square of the coupling constant $- ln (| J^{2} |)$ . (b) QD PLE spectra for resonant QW excitation calculated within Bloch equation model as a function of $- ln (| J^{2} |)$ . (c) Simulated PLE spectra for various values of $- ln (| J^{2} |)$ .Reuse & Permissions
Figure 5
(Color online) (a) Time-resolved femtosecond differential reflectivity spectra $Δ R (λ, Δ t) / R_{0} (λ)$ of a hybrid QW/QD sample with a barrier thickness of 5 nm. Orthogonally pump and probe pulses with a wavelength of 920 nm are centered at the QW exciton resonance. The $Δ R$ spectra show (i) at positive delay, $Δ t > 0$ , a pump-induced bleaching of the QW exciton resonance persisting for 25 ps, i.e., the QW lifetime and (ii) at negative delay, $Δ t < 0$ , spectral oscillations reflecting the perturbed free induction decay of the excitonic QW polarization. (b) Time dynamics of the differential reflectivity $Δ R (λ = h c / E^{X}, Δ t)$ probed at the QW exciton resonance (open circles). A single exponential decay of $Δ R$ with a lifetime $τ_{X} = 25 ps$ , reflecting the QW exciton lifetime, is observed. The weak prepulse and after pulse result from reflections of the pump and probe pulses at the rear side of the 0.65-mm-thick sample substrate. The solid line represents a fit to the data using a single-exponential decay.Reuse & Permissions

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