Asymmetric spin relaxation induced by the residual electron spin in semiconductor quantum dots (QDs) adjacent to a superlattice (SL) was studied using spin- and time-resolved photoluminescence under the selective photoexcitation of the SL miniband states. Spin-polarized electrons were photoexcited in the SL barrier and then injected into the QDs through spin-conserving tunneling. The spin-polarized electron transport and the faster transport of the electrons as compared to the holes generate the residual majority electron spins in the QDs. A reversal of the optical spin polarity was observed at the ground state of the QDs, depending on the excitation powers. A rate equation analysis considering the individual spin-flip times between spin-split QD states indicates that the polarity reversal originates from the asymmetric spin-flip process at the excited state of the QDs. The asymmetric spin relaxation is associated with the selective relaxation of the spin-flipped electron and hole to the unoccupied ground state, which is induced by the existence of the residual majority electron spin at this state. In addition, we observed a clear recovery of the optical spin polarity by eliminating the existence of the residual electron spin through heavy p-doping. These findings are important to attain a fundamental understanding of the spin relaxation mechanism within the QDs and provide an insight into the manipulation of the optical spin polarity by controlling the residual electron spins in the QDs.

中文翻译：

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半导体量子点超晶格混合纳米系统中残余电子自旋引起的不对称自旋弛豫

在 SL 微带态的选择性光激发下，使用自旋和时间分辨光致发光研究了由与超晶格 (SL) 相邻的半导体量子点 (QD) 中的残余电子自旋引起的不对称自旋弛豫。自旋极化电子在 SL 势垒中被光激发，然后通过自旋守恒隧道注入 QD。与空穴相比，自旋极化电子传输和更快的电子传输在 QD 中产生剩余的多数电子自旋。根据激发功率，在 QD 的基态观察到光学自旋极性的反转。考虑自旋分裂 QD 状态之间的单个自旋翻转时间的速率方程分析表明，极性反转源自 QD 激发态的不对称自旋翻转过程。不对称自旋弛豫与自旋翻转的电子和空穴选择性弛豫到未占据的基态有关，这是由该状态下剩余多数电子自旋的存在引起的。此外，我们通过重 p 掺杂消除了残留电子自旋的存在，观察到了光学自旋极性的明显恢复。这些发现对于获得对 QD 内自旋弛豫机制的基本理解很重要，并通过控制 QD 中的残余电子自旋来深入了解光学自旋极性的操纵。