James Franck Institute, The University of Chicago , 929 East 57th Street, Chicago, Illinois 60637, United States.
ACS Nano. 2017 Apr 25;11(4):4165-4173. doi: 10.1021/acsnano.7b01014. Epub 2017 Mar 21.
The absolute positions of the energy levels of colloidal quantum dots of Hg(S, Se, Te), which are of interest as mid-infrared materials, are determined by electrochemistry. The bulk valence bands are at -5.85, -5.50, and -4.77 eV (±0.05 eV) for zinc-blend HgS, HgSe, HgTe, respectively, in the same order as the anions p-orbital energies. The conduction bands are conversely at -5.20, -5.50, and -4.77 eV. The stable ambient n-doping of Hg(S, Se) quantum dots compared to HgTe arises because the conduction band is sufficiently lower than the measured environment Fermi level of ∼ -4.7 eV to allow for n-doping for HgS and HgSe quantum dots even with significant electron confinement. The position of the Fermi level and the quantum dots states are reported for a specific surface treatment with ethanedithiol and electrolyte environment. The positions are however sensitive to different surface treatments, providing an avenue to control doping. Electrochemical gating is further used to determine the carrier mobility in the films of the three different systems as a function of CQD size. HgSe and HgS show increasing mobility with increasing particle sizes while HgTe shows a nonmonotonous behavior, which is attributed to some degree of aggregation of HgTe QDs.
胶体量子点的能级位置是通过电化学确定的，这些胶体量子点是作为中红外材料的 Hg(S, Se, Te) 的组成部分，具有重要意义。在锌矿结构的 HgS、HgSe 和 HgTe 中，价带的位置分别为-5.85 eV、-5.50 eV 和-4.77 eV（±0.05 eV），这与阴离子 p 轨道能量的顺序一致。相反，导带的位置分别为-5.20 eV、-5.50 eV 和-4.77 eV。与 HgTe 相比，Hg(S, Se)量子点在稳定环境中的 n 型掺杂更为稳定，这是因为导带足够低于测量到的环境费米能级（约-4.7 eV），允许 HgS 和 HgSe 量子点即使在电子限制很大的情况下进行 n 型掺杂。本文报道了特定的乙二硫醇表面处理和电解质环境下费米能级和量子点态的位置。然而，这些位置对不同的表面处理很敏感，为控制掺杂提供了一种途径。电化学门控进一步用于确定三个不同体系的薄膜中的载流子迁移率作为 CQD 尺寸的函数。HgSe 和 HgS 的迁移率随着颗粒尺寸的增加而增加，而 HgTe 则表现出非单调行为，这归因于 HgTe QD 一定程度的聚集。
