Electronic structure of cleaved clean and oxygen-covered GaAs (110) surfaces
Electronic structure of cleaved clean and oxygen-covered GaAs (110) surfaces
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解理清洁且氧覆盖的 GaAs (110) 表面的电子结构
DOI：
10.1103/physrevb.15.865
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发表时间：
1977
期刊：
影响因子：
--
通讯作者：
R. Matz
中科院分区：
文献类型：
--
作者：
H. Lüth;M. Büchel;R. Dorn;M. Liehr;R. Matz
利用椭偏仪、表面光电压光谱（SPV）和低能电子损失光谱（ELS）研究了超高真空中裂解的$p$型和$n$型晶体的GaAs（110）表面。由于氧吸附引起的空间电荷层中的Franz-Keldysh效应引起的椭圆偏角$\ensuremath{\delta}\ensuremath{\Delta}$的变化表明，氧吸附在（\ensuremath{\sim} 1 langmuir, 1 L = ${10}^{\ensuremath{-}6}$ Torr sec）剂量下对清洁表面的能带弯曲的改变远低于产生可测量的俄歇电子信号的剂量。在SPV光谱中，在干净的完全切割（110）表面上，在禁止带中无法检测到空的或占据的表面状态，而氧吸附和/或晶体学缺陷会产生这种状态。在晶体不规则性上，氧还诱导出一组新的接近价态或导带边缘的外在表面态。ELS数据结合SPV结果支持从表面激子角度解释$\mathrm{Ga}(3d)\ensuremath{-}\mathrm{G}\mathrm{a}$（表面态）跃迁。ELS进一步表明了Ga表面原子对氧的化学吸附键的贡献。椭偏光谱和SPV光谱的结果可以用吸附氧诱导中隙附近两组离散表面态的模型来理解。
GaAs (110) surfaces of $p$- and $n$-type crystals cleaved in ultrahigh vacuum are investigated by ellipsometry, surface photovoltage (SPV) spectroscopy and low-energy-electron loss spectroscopy (ELS). Changes of the ellipsometric angle $\ensuremath{\delta}\ensuremath{\Delta}$ which are induced by a Franz-Keldysh effect in the space-charge layer due to adsorbed oxygen indicate that oxygen adsorption changes the band bending of the clean surface at dosages (\ensuremath{\sim} 1 langmuir, 1 L = ${10}^{\ensuremath{-}6}$ Torr sec) much lower than those which produce measurable Auger-electron signals. In SPV spectroscopy on a clean perfectly cleaved (110) surface empty or occupied surface states can not be detected in the forbidden band whereas oxygen adsorption and/or crystallographic defects produce such states. On crystallographic irregularities oxygen also induces a new set of extrinsic surface states close to the valence or the conduction-band edge. The ELS data in combination with SPV results support the interpretation of the $\mathrm{Ga}(3d)\ensuremath{-}\mathrm{G}\mathrm{a}$ (surface state) transition in terms of a surface exciton. ELS furthermore suggests a contribution of Ga surface atoms to the chemisorption bond of oxygen. The results from ellipsometry and SPV spectroscopy can be understood by means of a model in which two discrete sets of surface states near midgap are induced by adsorbed oxygen.