Mechanism of microwave-induced photoluminescence modulation and optically detected resonances due to a two-dimensional electron gas in a heterostructure

I. Baskin, B. M. Ashkinadze, E. Cohen, and L. N. Pfeiffer

Phys. Rev. B 78, 195318 – Published 19 November 2008

Abstract

The effect of pulsed microwave (mw) irradiation (at 36 GHz) on the photoluminescence (PL) of modulation-doped GaAs/AlGaAs quantum wells (MDQWs) containing a two-dimensional electron gas (2DEG) is studied by time-resolved spectroscopy at an ambient temperature of 2 K. The temporal response of the two-dimensional electron-hole PL to a short mw pulse reveals remarkable PL intensity kinetics with overshoots and a long decay time $(> 10 ns)$ after the mw pulse terminates. The observed effects are explained by the temporal evolution of the energy redistribution of photoexcited holes. This redistribution is caused by nonequilibrium, long-lived acoustic phonons that are emitted by the mw heated 2DEG and are absorbed by the holes. Optically detected resonances (ODRs) of the 2DEG are observed in both the two-dimensional electron-hole PL band and in the PL line of excitons that are photoexcited in the undoped superlattice adjoining the MDQW. This provides an experimental proof that the emitted acoustic phonons propagate ballistically throughout the entire heterostructure and induce an effective, long range, indirect interaction between the mw heated 2DEG and the holes (as well as with the spatially separated excitons). This interaction constitutes the underlying mechanism of the mw-induced ODRs observed in heterostructures containing a 2DEG.

Received 30 June 2008

DOI:https://doi.org/10.1103/PhysRevB.78.195318

Authors & Affiliations

I. Baskin, B. M. Ashkinadze, and E. Cohen

Solid State Institute, Technion-Israel Institute of Technology, Haifa 32000, Israel

L. N. Pfeiffer

Bell Laboratories, Alcatel-Lucent Technologies, Murray Hill, New Jersey 07974, USA

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Vol. 78, Iss. 19 — 15 November 2008

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Images

Figure 1
The 2De-h photoluminescence (a) and microwave-modulated PL (b) spectra $(T_{L} = 2 K)$ . Curve 1 was obtained without mw irradiation, and all other with cw mw power of: $P_{mw}$ =0.5 mW—curves 2 and 4; $P_{mw}$ =2 mW—curves 3 and 5; $P_{mw}$ =20 mW—curve 6. Inset: a schema of 2DEG-hole optical transitions where G is photogeneration, and $ε_{h}$ shows a highest energy of the holes recombining with the 2DEG. $τ_{ε}^{h}$ and $τ_{R}$ are the relaxation and 2DEG-h recombination times, respectively. The solid lines in (a) display the PL spectra calculated using Eq. (1) with the fixed values of $E_{F} = 7.2 meV$ , $Γ = 0.7 meV$ , $m_{h} = 0.35 m_{0}$ , and with the following $T_{e}$ and $T_{h}$ fitting parameters: 1.9 and 2.5 K (curve 1); 3.4 and 4.9 K (curve 2); 9 and 20 K (curve 3).Reuse & Permissions
Figure 2
Transient PL spectra (at $P_{mw} \sim 2 mW$ ) measured at several delay times relative to the mw pulse leading edge, as shown by the corresponding symbols in the inset. Inset: Temporal dependence of the spectrally integrated PL intensity (solid line) and the mw pulse (dashed line).Reuse & Permissions
Figure 3
Transient PL intensity traces measured under a mw pulse (100 ns) at $B_{CR} = 0.085 T$ . Curve 1 in (a) shows the mw pulse waveform. (a) PL intensity monitored at $E_{m} = 1.524 eV$ for the following $P_{mw}^{B}$ : 0.05 mW—curve 2; 0.2 mW—curve 3; 0.5 mW—curve 4; 1 mW—curve 5. $J_{0}$ is the PL intensity at $P_{mw} = 0$ . (b) Transient MPL intensity monitored at several $E_{m}$ values and at $P_{mw}^{B} = 0.3 mW$ $(B = 0.085 T)$ .Reuse & Permissions
Figure 4
$J (B)$ (ODR traces) and the mw absorption dependence on $B$ (bottom curves). (a) $J (B)$ traces obtained in a rectangular $2 \times 1 {mm}^{2}$ sample. Open circles and triangles show the $J (B)$ measured within the 2De-h PL band $(E_{m} = 1.524 eV)$ at $P_{mw} = 0.02$ and 3 mW, respectively. Square symbols display the $J (B)$ dependence monitored at u-SL exciton PL line $(E_{m} = 1.599 eV, P_{mw} = 0.2 mW)$ . Top panel of (b) displays the sample structure containing the MDQW between two SLs. The corresponding 2De-h and exciton u-SL PL spectra are obtained at $P_{mw} = 0$ and 0.05 mW. (b) $J (B)$ dependencies measured at $E_{m} = 1.524 eV$ and $E_{m} = 1.599 eV$ in a mesa sample of 0.5 mm diameter. $J_{0}$ is the PL intensity at $P_{mw} = 0$ . Bottom curve is the corresponding mw absorption trace.Reuse & Permissions
Figure 5
(a) $T_{e} (t)$ (dashed curve) and $T_{h} (t)$ (solid curve) dependencies used in simulation of the transient PL. Dotted curve shows the mw pulse wave form. (b) Transient MPL signals at several PL energies simulated by Eq. (1) and using the $T_{e} (t)$ , $T_{h} (t)$ dependencies shown in Fig. 5a. (c) Dashed curve displays the solution of Eq. (3) for the transient “radiative hole” density [Eq. (4)] with $τ^{h} (t)$ is taken as the square shaped function (0.5–1 ns). Solid curve presents the numerical solution of Eq. (3), where $τ^{h} (t)$ dependence shown by dotted curve was used. (d) MPL transient signals where the transient hole redistribution $p_{2} (t)$ (c) is taken into account.Reuse & Permissions

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