Giant bowing of the band gap and spin-orbit splitting energy in GaP1-xBix dilute bismide alloys
Giant bowing of the band gap and spin-orbit splitting energy in GaP1-xBix dilute bismide alloys
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DOI：
10.1038/s41598-019-43142-5
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发表时间：
2019-05-02
影响因子：
4.6
通讯作者：
Sweeney, Stephen J.
中科院分区：
文献类型：
--
作者：
Bushell, Zoe L.;Broderick, Christopher A.;Sweeney, Stephen J.
利用椭圆偏振光谱测量了x=3.7%的GaP_(1-x)Bix/GaP外延层，观察到了直接带隙(E-g(Gamma))和价带自旋轨道分裂能(Delta(SO))的巨大弯曲。E-g(Gamma)(Delta(So))被测量为在掺入1%Bi的情况下减少(增加)约200 meV(240 MeV)，对应于从GaP到GaP0.99Bi0.01的Delta(So)增加四倍以上。E-g(Gamma)和Delta(So)随x的演化以强烈的成分依赖的弯曲为特征。我们证明了一个简单的价带反腐蚀模型，它直接从原子超晶胞计算中参数化，定量地描述了测量到的E-g(Gamma)和Delta(So)随x的演化。与研究得很好的GaAs1-xBix合金不同，在GaP1-xBix中，Bi位在GaP基质带隙内产生了能量很高的局域杂质态。这导致了双杂化态的光学活性带的出现，解释了E-g(Gamma)和Delta(So)的整体大弯曲，特别是对x小于或类似于1%的巨型弯曲。我们的分析揭示了铋作为等价杂质的作用，并首次对GaP_(1-x)Bix合金能带结构进行了详细的实验和理论分析。
Using spectroscopic ellipsometry measurements on GaP1-xBix/GaP epitaxial layers up to x=3.7% we observe a giant bowing of the direct band gap (E-g(Gamma)) and valence band spin-orbit splitting energy (Delta(SO)). E-g(Gamma) (Delta(SO)) is measured to decrease (increase) by approximately 200 meV (240 meV) with the incorporation of 1% Bi, corresponding to a greater than fourfold increase in Delta(SO) in going from GaP to GaP0.99Bi0.01. The evolution of E-g(Gamma) and Delta(SO) with x is characterised by strong, composition-dependent bowing. We demonstrate that a simple valence band-anticrossing model, parametrised directly from atomistic supercell calculations, quantitatively describes the measured evolution of E-g(Gamma) and Delta(SO) with x. In contrast to the well-studied GaAs1-xBix alloy, in GaP1-xBix substitutional Bi creates localised impurity states lying energetically within the GaP host matrix band gap. This leads to the emergence of an optically active band of Bi-hybridised states, accounting for the overall large bowing of E-g(Gamma) and Delta(SO) and in particular for the giant bowing observed for x less than or similar to 1%. Our analysis provides insight into the action of Bi as an isovalent impurity, and constitutes the first detailed experimental and theoretical analysis of the GaP1-xBix alloy band structure.