再谈PbS量子点薄膜的价和导带尺寸依赖性,ACS Nano

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再谈PbS量子点薄膜的价和导带尺寸依赖性
ACS Nano ( IF 15.8 ) Pub Date : 2016-02-26 00:00:00 , DOI: 10.1021/acsnano.5b06833
Elisa M. Miller ₁ , Daniel M. Kroupa _{1,

2} , Jianbing Zhang ₁ , Philip Schulz ₃ , Ashley R. Marshall _{1,

2} , Antoine Kahn ₃ , Stephan Lany ₁ , Joseph M. Luther ₁ , Matthew C. Beard ₁ , Craig L. Perkins ₁ , Jao van de Lagemaat ₁

Affiliation

我们使用块状PbS的高信噪比X射线光电子能谱，GW计算以及假设抛物线的模型来揭示块状PbS的各种X射线和紫外光电子能谱特征，并确定如何进行最佳分析PbS量子点（QD）薄膜的价带区域。X射线和紫外光电子能谱（XPS和UPS）通常用于探测晶体半导体和薄膜半导体的费米能级和价带最大值（VBM）之间的差异。但是，我们发现，当将标准XPS / UPS分析用于PbS时，由于VBM处的状态密度低，结果通常不切实际。取而代之的是，使用抛物线能带模型来确定PbS QD薄膜的VBM，该模型基于整体PbS实验光谱和整体GW计算。我们的分析突出了大带隙，高量子限制的PbS QD的能带图的布里渊带表示形式的细分。我们还确定，在1,2-乙二硫醇处理过的PbS QD薄膜中，费米能级位置取决于QD尺寸。具体地，对于较大的带隙PbS QD膜，最小的带隙QD膜具有接近导带最小值的费米能级，并且费米能级远离导带移动。QD带隙内费米能级的这种变化可能是由于Pb：S比的变化所致。另外，我们使用逆光电子能谱法测量导带区域，由于接近导带最小值的低状态密度，在分析PbS QD膜时也面临类似的挑战。

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Revisiting the Valence and Conduction Band Size Dependence of PbS Quantum Dot Thin Films

We use a high signal-to-noise X-ray photoelectron spectrum of bulk PbS, GW calculations, and a model assuming parabolic bands to unravel the various X-ray and ultraviolet photoelectron spectral features of bulk PbS as well as determine how to best analyze the valence band region of PbS quantum dot (QD) films. X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS) are commonly used to probe the difference between the Fermi level and valence band maximum (VBM) for crystalline and thin-film semiconductors. However, we find that when the standard XPS/UPS analysis is used for PbS, the results are often unrealistic due to the low density of states at the VBM. Instead, a parabolic band model is used to determine the VBM for the PbS QD films, which is based on the bulk PbS experimental spectrum and bulk GW calculations. Our analysis highlights the breakdown of the Brillioun zone representation of the band diagram for large band gap, highly quantum confined PbS QDs. We have also determined that in 1,2-ethanedithiol-treated PbS QD films the Fermi level position is dependent on the QD size; specifically, the smallest band gap QD films have the Fermi level near the conduction band minimum and the Fermi level moves away from the conduction band for larger band gap PbS QD films. This change in the Fermi level within the QD band gap could be due to changes in the Pb:S ratio. In addition, we use inverse photoelectron spectroscopy to measure the conduction band region, which has similar challenges in the analysis of PbS QD films due to a low density of states near the conduction band minimum.

更新日期：2016-02-26

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