The authors present the results of the photoluminescence characterization of three asymmetric triple quantum well (ATQW) systems. Each one contains three ultrathin CdSe quantum wells of 1, 2, and 3 monolayers (ML) thickness grown by atomic layer epitaxy between ZnSe separating barriers. Two systems have coupled QWs due to thin 5 nm thick ZnSe separating barriers, and the uncoupled system has 100 nm ZnSe separating barriers. Two of them (5 and 100 nm ZnSe barriers) were grown in the sequence 3–2–1, with the 3 ML QW closer to the substrate, while the third ATQW (5 nm ZnSe barrier) was grown in the reverse order. The photoluminescence spectrum of the uncoupled ATQW (3–2–1 sequence) presents three excitonic peaks, one peak for each QW, with the same emission energies of corresponding isolated single QWs. In the case of two coupled ATQW systems (3–2–1 and 1–2–3 growth sequence), the authors observed only one peak, corresponding to the lowest transition energy in the system formed by the three coupled QWs. The calculation of the wavefunctions shows no overlap for 100 nm ZnSe separating barriers, as expected for this thick barrier. For the systems with 5 nm ZnSe barriers, the calculations indicate that the overlap occurs mainly between the wavefunctions of the central 2 ML thick CdSe QW and the neighboring 1 ML and 3 ML QW wavefunctions; the overlap between the 1 and 3 ML QWs is small as a consequence of their 10 nm separation. The authors found that the effect of the coupling between the QWs is more easily identified by the reduction (or absence) of the intensity of the higher energy transitions of the multiple QW system than by the change of the ATQW energy levels with barrier thickness reduction.

中文翻译：

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外延非对称三重 CdSe 量子阱的光致发光特性

作者展示了三个不对称三量子阱 (ATQW) 系统的光致发光表征结果。每个包含三个超薄 CdSe 量子阱，厚度为 1、2 和 3 个单层 (ML)，通过 ZnSe 分离势垒之间的原子层外延生长。由于薄的 5 nm 厚的 ZnSe 分离势垒，两个系统已耦合 QW，而未耦合系统具有 100 nm 的 ZnSe 分离势垒。其中两个（5 和 100 nm ZnSe 势垒）以 3-2-1 的顺序生长，3 ML QW 更靠近基板，而第三个 ATQW（5 nm ZnSe 势垒）以相反的顺序生长。未耦合的 ATQW（3-2-1 序列）的光致发光光谱呈现三个激子峰，每个 QW 一个峰，具有相同的相应孤立单个 QW 的发射能量。在两个耦合的 ATQW 系统（3-2-1 和 1-2-3 生长序列）的情况下，作者仅观察到一个峰值，对应于由三个耦合 QW 形成的系统中的最低跃迁能量。波函数的计算表明 100 nm ZnSe 分离势垒没有重叠，正如这个厚势垒所预期的那样。对于具有 5 nm ZnSe 势垒的系统，计算表明重叠主要发生在中央 2 ML 厚 CdSe QW 的波函数与相邻的 1 ML 和 3 ML QW 波函数之间；1 和 3 ML QW 之间的重叠很小，因为它们的间隔为 10 nm。