Current Optics and Photonics

Optical Society of Korea (한국광학회)
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Two-dimensional Nature of Center-of-mass Excitons Confined in a Single CdMnTe/CdTe/CdMnTe Heterostructure

  • Lee, Woojin (Department of Cogno-Mechatronics Engineering, Physics Education, Pusan National University) ;
  • Kim, Minwoo (Department of Cogno-Mechatronics Engineering, Physics Education, Pusan National University) ;
  • Yang, Hanyi (Department of Cogno-Mechatronics Engineering, Physics Education, Pusan National University) ;
  • Kyhm, Kwangseuk (Department of Cogno-Mechatronics Engineering, Physics Education, Pusan National University) ;
  • Murayama, Akihiro (Graduate School of Information Science and Technology, Hokkaido University) ;
  • Kheng, Kuntheak (CEA, INAC-SP2M, Nanophysique et Semiconducteurs Group) ;
  • Mariette, Henri (CEA, INAC-SP2M, Nanophysique et Semiconducteurs Group) ;
  • Dang, Le Si (Department of NANOscience, Institut Neel, CNRS)
  • Received : 2018.11.11
  • Accepted : 2018.11.23
  • Published : 2018.12.25
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Abstract

We have investigated the dimensional nature of center-of-mass exciton confinement states in a CdMnTe/CdTe/CdMnTe heterostructure, where the CdTe well is too wide (144 nm) to confine both electrons and holes but able to confine whole excitons in the center-of-mass coordinate. Fine multiple photoluminescence spectra with a few meV separation were observed at 6 K. From the thickness dependence of the transition rate, they were attributed to even numbered center-of-mass exciton confinement states (N = 2, 4, 6, ${\cdots}$, 18). Dimensionality of the center-of-mass exciton confinement states was also investigated in terms of temperature dependence of radiative decay time. At low temperatures (${\leq}12K$), we found that the ground state excitons are likely localized possibly due to the barrier interface fluctuation, resulting in a constant decay time (~350 ps). With increased temperature (${\geq}12K$), localized excitons are thermally released, giving rise to a linear temperature dependence of radiative decay time as an evidence of two-dimensional nature.

Keywords

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FIG. 1. (a) The center-of-mass excitons are weakly confined in an intermediate size (~102 nm) compared to strongly confined excitons of thin quantum wells (<10 nm) and unconfined excitons of bulk. (b) When a CdTe layer (a = 144 nm) is sandwiched between two Cd0.9Mn0.1Te layers, only the even numbered CMX confinement states (N =2, 4, 6, 8, 10, ⋯, 18) are dominant. (c) PL spectrum at 4 K. The dominant PL peak near 1595 meV is involved with three CMX confinement states (N = 2, 4, 6). (d) CMX-polariton dispersion.

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FIG. 2. (a) Schematic diagram of excitation-correlation (EC) spectroscopy, where excitation of a delayed pulse pair gives rise to correlated emission signals (b). (c) Characteristic decay time (τc) for the excited CMX states. (d) Spectral intensity of EC signals for delay time (τ).

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FIG. 3. Time-integrated PL spectrum at 6 K (a), 18 K (b), 30 K (c) are fitted with two Gaussian functions to analyze (American English) the resolution-limited three (N = 2, 4, 6) confinement states (X) and other (N = 8, 10, ⋯, 18) excited states (X*), whereby temperature dependence of the central peak energy (d), linewidth (e), and normalized quantum efficiency (f) are obtained.

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FIG. 4. Time-resolved PL intensity of X (N = 2, 4, 6) (a) and X* (N = 8, 10, ⋯, 18) (b) were measured for increasing temperature, whereby temperature dependence of the radiative decay times (c) were also obtained. A theoretical model [28] (dotted line) of temperature dependent radiative recombination time (dotted line) was also compared, which suggest that the CMX confinement states show a two-dimensional nature when thermal energy is large enough (≲12 K).

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