Chemistry & Nanoscience Center, National Renewable Energy Laboratory , Golden, Colorado 80401, United States.
Department of Chemistry and Biochemistry, University of Colorado , Boulder, Colorado 80309, United States.
J Am Chem Soc. 2017 Aug 2;139(30):10382-10394. doi: 10.1021/jacs.7b04551. Epub 2017 Jul 24.
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.
电子杂质掺杂体半导体是半导体科学与技术的重要组成部分。然而，仅有少数研究证明了半导体纳米晶体中电子杂质的控制。在这里，我们通过后合成的阳离子交换反应研究了胶体 PbSe 量子点（QD）的电子杂质掺杂，其中 Pb 被 Ag 取代。我们发现，改变暴露于合成的 PbSe QD 的掺杂剂浓度可以控制交换的程度。电子杂质掺杂的 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。光电子能谱证实 Ag 是 PbSe QD 的 p 型掺杂剂，而红外光谱与带内跃迁能量的 k·p 计算一致。我们发现，要使第一激子跃迁平均漂白 1 个载流子/ QD，需要大约 10%的 Pb 被 Ag 取代。我们假设大部分掺入的 Ag 仍留在 QD 表面，并且不与 QD 的核心电子态相互作用。相反，表面过剩的 Ag 促进了<1% Ag 掺入 QD 核心，从而导致 p 型掺杂行为。
