Electronic impurity doping of bulk semiconductors is an essential component of semiconductor science and technology. Yet there are only a handful of studies demonstrating control of electronic impurities in semiconductor nanocrystals. Here, we studied electronic impurity doping of colloidal PbSe quantum dots (QDs) using a postsynthetic cation exchange reaction in which Pb is exchanged for Ag. We found that varying the concentration of dopants exposed to the as-synthesized PbSe QDs controls the extent of exchange. The electronic impurity doped QDs exhibit the fundamental spectroscopic signatures associated with injecting a free charge carrier into a QD under equilibrium conditions, including a bleach of the first exciton transition and the appearance of a quantum-confined, low-energy intraband absorption feature. Photoelectron spectroscopy confirms that Ag acts as a p-type dopant for PbSe QDs and infrared spectroscopy is consistent with k·p calculations of the size-dependent intraband transition energy. We find that to bleach the first exciton transition by an average of 1 carrier per QD requires that approximately 10% of the Pb be replaced by Ag. We hypothesize that the majority of incorporated Ag remains at the QD surface and does not interact with the core electronic states of the QD. Instead, the excess Ag at the surface promotes the incorporation of <1% Ag into the QD core where it causes p-type doping behavior.

中文翻译：

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掺银PbSe量子点的合成与光谱学

体半导体的电子杂质掺杂是半导体科学和技术的重要组成部分。然而，仅有少数研究证明了对半导体纳米晶体中电子杂质的控制。在这里，我们使用其中Pb交换为Ag的后合成阳离子交换反应研究了胶体PbSe量子点（QDs）的电子杂质掺杂。我们发现，改变暴露于合成的PbSe QD的掺杂剂的浓度可以控制交换的程度。掺杂电子杂质的QD表现出与在平衡条件下将自由电荷载流子注入QD相关的基本光谱学特征，包括第一激子跃迁的漂白和量子限制的低能带内吸收特征的出现。大小相关的带内跃迁能量的k · p计算。我们发现，要使每个QD的第一个激子跃迁平均减少1个载流子，就需要用Ag代替大约10％的Pb。我们假设掺入的大部分Ag保留在QD表面，并且不与QD的核心电子态相互作用。相反，表面上过量的Ag会促使<1％Ag掺入QD核中，从而导致p型掺杂行为。