角分辨光电子能谱
直接和间接带隙
激子
带隙
材料科学
凝聚态物理
单层
光电发射光谱学
半导体
价(化学)
半金属
Crystal(编程语言)
光谱学
电子结构
分子物理学
谱线
化学
物理
光电子学
纳米技术
量子力学
有机化学
计算机科学
程序设计语言
天文
作者
Matthew J. Hamer,Johanna Zultak,Anastasia V. Tyurnina,Viktor Zólyomi,Daniel Terry,Alexei Barinov,Alistair Garner,Jack Donoghue,Aidan P. Rooney,Viktor Kandyba,Alessio Giampietri,Abigail Graham,Natalie C. Teutsch,Xue Xia,Maciej Koperski,Sarah J. Haigh,Vladimir I. Fal’ko,Р. В. Горбачев,Neil R. Wilson
出处
期刊:ACS Nano
[American Chemical Society]
日期:2019-01-25
被引量:81
标识
DOI:10.1021/acsnano.8b08726
摘要
Atomically thin films of III-VI post-transition metal chalcogenides (InSe and GaSe) form an interesting class of two-dimensional semiconductors that feature a strong variation of their band gap as a function of the number of layers in the crystal and, specifically for InSe, an expected crossover from a direct gap in the bulk to a weakly indirect band gap in monolayers and bilayers. Here, we apply angle-resolved photoemission spectroscopy with submicrometer spatial resolution (μARPES) to visualize the layer-dependent valence band structure of mechanically exfoliated crystals of InSe. We show that for one-layer and two-layer InSe the valence band maxima are away from the Γ-point, forming an indirect gap, with the conduction band edge known to be at the Γ-point. In contrast, for six or more layers the band gap becomes direct, in good agreement with theoretical predictions. The high-quality monolayer and bilayer samples enable us to resolve, in the photoluminescence spectra, the band-edge exciton (A) from the exciton (B) involving holes in a pair of deeper valence bands, degenerate at Γ, with a splitting that agrees with both μARPES data and the results of DFT modeling. Due to the difference in symmetry between these two valence bands, light emitted by the A-exciton should be predominantly polarized perpendicular to the plane of the two-dimensional crystal, which we have verified for few-layer InSe crystals.
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