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Reynolds, D. C.; Evans, K. R.; Merkel, Kenneth G.; Stutz, C. E.; Yu, P. W.

doi:10.1103/physrevb.43.9087

Cited by 6 publications

(2 citation statements)

References 24 publications

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“…We attribute line L to a localized indirect exciton (LIX): the indirect exciton 1 bound to an impurity or interface defect. Support for this comes from the size of the redshift which is close to the binding energy of bound excitons in GaAs QWs [20]. Line L disappears for T > 10 K while line 1 remains and this is consistent with the dissociation of localized excitons (which have only a small density of states) into free excitons with increasing temperature.…”

Section: Resultsmentioning

confidence: 65%

Luminescence of excitons in slightly asymmetric double quantum wells

et al. 1997

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We report the first studies of exciton luminescence spectra from asymmetric double quantum wells (DQWs) of very similar width. The DQWs were of GaAs/AlGaAs and the differences in widths of the coupled wells were one or two monolayers. The coupled direct and indirect exciton states anticross with a resonance splitting of 1.33 meV. An additional luminescence line appearing at low temperatures is identified as a localized indirect exciton.An asymmetric double quantum well (DQW) in which the two QWs are separated by a narrow barrier gives rise to a minimum of four luminescence lines. Two of these are due to recombination of so-called direct exciton (DX) states in which the electron and hole are in the same quantum well and two to indirect exciton (IX) states in which the electron and hole are in different wells [1][2][3][4][5][6]. A number of optical studies have been made of these systems and of the changes in line positions when the relative positions of the energy levels in the two QWs are shifted by an applied electric field F. The energies of the indirect excitons vary approximately linearly with F while those of the direct excitons are approximately fixed. As a result, the DX and IX lines cross or rather anticross since the electrons involved in both emission processes can tunnel through the barrier separating the wells. (In principle this can also happen for holes but in this case the tunnelling rate is too small to produce measurable effects.)In previous studies of such systems [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17], the widths of the coupled quantum wells differed by several monolayers leading to differences in the DX energies of 10 meV or more. In the present work however, the DQWs are only slightly asymmetric, the widths of the coupled QWs differing by only 1 or 2 monolayers (MLs). The main purpose of working with such systems is that they have the potential to operate as tunable spectrometers of non-equilibrium acoustic phonons in the important range below 1000 GHz in which phonons propagate ballistically through material such as GaAs allowing the possibility of detailed study of relaxation and other processes. This work will be discussed in a later paper. In the course of investigating these systems however we have found that the spectroscopic properties of the devices used are very well defined and, of particular note, provide the first observation of indirect exciton localization. It is that aspect of the work that is reported here.

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Section: Resultsmentioning

confidence: 65%

Luminescence of excitons in slightly asymmetric double quantum wells

et al. 1997

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“…2b). We attribute this to a localized indirect bound exciton since the size of its red-shift relative to IXW is close to the binding energy of excitons in GaAs QWs [6]. Line L disappears for T > 10 K while line 1 remains and this is consistent with the dissociation of localized excitons (which have only a small density of states) into free excitons with increasing temperature.…”

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confidence: 52%

Tunnelling of Direct and Indirect Excitons in Slightly Asymmetric Double Quantum Wells

et al. 1996

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We report the first studies of luminescence spectra from asymmetric double quantum wells of GaAs with widths around 100 Å differing by only one (2.8 A) or two monolayers. Studies of the position and intensity of the direct and indirect exciton lines suggest the existence of acoustic phonon-assisted tunnelling between exciton states separated by a few meV. At temperatures 10-20 K the electron tunnelling process is fast enough to maintain thermal equilibrium between these direct and indirect excitons which are connected with holes in the same quantum well.PACS numbers: 73.20. Dx, 63.20.Kr In GaAs/AlGaAs double quantum wells (DQWs) electron and hole tunnelling through the thin barrier have been intensively studied by both cw and time-resolved luminescence techniques and it is clear that the tunnelling processes are signiflcantly modified by excitonic effects [1]. Much of this work was carried out on asymmetric DQWs in which the ground state energy differences in the two wells were appreciably more than 1 meV for both electrons and holes. For smaller energy differences, it has not yet been possible to separate the non-resonant tunnelling associated with acoustic phonons from that caused by elastic scattering from impurities and interface defects followed by phonon relaxation. For simplicity therefore we refer to the observed process as phonon-assisted tunnelling in the expectation that in our high quality samples this will turn out to be the stronger of the two. A theoretical analysis of these processes has been carried out [2,3] and a direct observation of acoustic phonon-assisted tunnelling in double barrier resonant tunnelling stuctures has been recently obtained using phonon pulses [4]. Detailed information on all these relaxation and tunnelling processes would be of value in the development of semiconductor nanostuctures as phonon spectrometers and generation at frequencies up to 1 ΤHz and above [2][3][4][5].In the present paper we are studying the cw photoluminescence from slightly asymmetric DQWs, in which the widths of the coupled QWs differ by only 1 or 2 monolayers (MLs). The paper is aimed particularly at extracting information on (895)

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4.2.2.1 Excitonic data and effects

Klingshirn¹

Landolt-Börnstein - Group III Condensed Matter

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Photoluminescence due to a bound-to-bound transition in a GaAs-Al0.3Ga0.7<

Cited by 6 publications

References 24 publications

Luminescence of excitons in slightly asymmetric double quantum wells

Luminescence of excitons in slightly asymmetric double quantum wells

Tunnelling of Direct and Indirect Excitons in Slightly Asymmetric Double Quantum Wells

4.2.2.1 Excitonic data and effects

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