Colloidal semiconductor quantum dots are attractive materials for the realization of solution-processable lasers. However, their applications as optical-gain media are complicated by a non-unity degeneracy of band-edge states, because of which multiexcitons are required to achieve the lasing regime. This increases the lasing thresholds and leads to very short optical gain lifetimes limited by nonradiative Auger recombination. Here, we show that these problems can be at least partially resolved by employing not neutral but negatively charged quantum dots. By applying photodoping to specially engineered quantum dots with impeded Auger decay, we demonstrate a considerable reduction of the optical gain threshold due to suppression of ground-state absorption by pre-existing carriers. Moreover, by injecting approximately one electron per dot on average, we achieve a more than twofold reduction in the amplified spontaneous emission threshold, bringing it to the sub-single-exciton level. These measurements indicate the feasibility of ‘zero-threshold’ gain achievable by completely blocking the band-edge state with two electrons.

中文翻译：

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使用带电半导体量子点实现零阈值光学增益

胶体半导体量子点是用于实现可溶液处理的激光器的有吸引力的材料。然而，它们作为光增益介质的应用由于带边缘状态的非统一简并化而变得复杂，因此，需要多激子来实现激射状态。这增加了激射阈值，并导致非常短的光学增益寿命，该寿命受到非辐射俄歇复合作用的限制。在这里，我们表明，通过采用非中性但带负电荷的量子点，这些问题至少可以得到部分解决。通过对受阻俄歇衰减的特殊设计的量子点进行光掺杂，我们证明了由于抑制了已有载流子对基态吸收的影响，光学增益阈值大大降低了。此外，平均每个点注入约一个电子，我们将放大的自发发射阈值降低了两倍以上，使其达到了亚单激子水平。这些测量结果表明通过用两个电子完全阻断带边缘状态可以实现“零阈值”增益的可行性。