Transition from parabolic to ring-shaped valence band maximum in few-layer GaS, GaSe, and InSe
Transition from parabolic to ring-shaped valence band maximum in few-layer GaS, GaSe, and InSe
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DOI：
10.1103/physrevb.90.235302
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发表时间：
2014-12-01
影响因子：
3.7
通讯作者：
Obraztsova, Elena D.
中科院分区：
文献类型：
--
作者：
Rybkovskiy, Dmitry V.;Osadchy, Alexander V.;Obraztsova, Elena D.
通过在密度泛函理论框架下进行第一性原理电子结构计算，我们研究了几层III-VI族晶体（GaS，GaSe和InSe）的价带形状对厚度的依赖性。我们估计了从块状抛物线到环状价带的临界转变厚度。直接超原胞计算表明，β-GaS和β-GaSe中价带的环形极值分别出现在6个四层（近似4.6 nm）和8个四层（近似6.4 nm）以下。区域折叠计算估计β-InSe临界厚度等于28个四层（类似于24.0 nm）。环形价带最大值的起源可以用k.p理论来理解，它提供了能带曲率和能带之间距离之间的联系。我们解释的厚度上的带形的依赖关系，以及两种类型的极端之间的过渡，由k-依赖的轨道组成的最高价带。我们发现，在临界厚度附近的有效质量的空穴在III-VI族化合物强烈依赖于tetralayer的数量。
By performing first-principles electronic structure calculations in frames of density functional theory we study the dependence of the valence band shape on the thickness of few-layer III-VI crystals (GaS, GaSe, and InSe). We estimate the critical thickness of transition from the bulklike parabolic to the ring-shaped valence band. Direct supercell calculations show that the ring-shaped extremum of the valence band appears in beta-GaS and beta-GaSe at a thickness below 6 tetralayers (similar to 4.6 nm) and 8 tetralayers (similar to 6.4 nm), respectively. Zone-folding calculations estimate the beta-InSe critical thickness to be equal to 28 tetralayers (similar to 24.0 nm). The origin of the ring-shaped valence band maximum can be understood in terms of k.p theory, which provides a link between the curvature of the energy bands and the distance between them. We explain the dependence of the band shape on the thickness, as well as the transition between two types of extremes, by the k-dependent orbital composition of the topmost valence band. We show that in the vicinity of critical thickness the effective mass of holes in III-VI compounds depends strongly on the number of tetralayers.