First principles calculation of optical spectra of GaAs growing surface structures

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We have developed the method to calculate the reflectance difference spectra (RDS) and clarified the electronic structures of growing semiconductor surfaces and interfaces from optical viewpoints as follows.1.Spectra origin and local field effect ; when the electronic states are localized (extended) around the surface/interface, the optical transitions between surface states (bulk states) produce peak-shaped (epsilon_2-derivative-shaped) spectra. From the various layr-thickness calculations, the local field is shown having about 50 contributions to the spectra.2.(001) anion surfaces ; the dangling-bond states of surface anion-dimer atoms produce the large peak structures in GaAs and ZnSe surface spectra. The peak position and width respectively increase by 0.77eV/ and 0.5eV/ with decreasing the dimer distance, which well explains the recent experiments by Kobayashi et al.3.(001) cation surfaces ; the cation atoms on the top layr largely sink into bulks to stabilize by producing sp^2/sp … More bonding, which stands up the dangling-bond states of the second-top-layr anions perpendicular to the surface. The optical transition from such states to the conduction-band states produces the characteristic peak structures, which feature is particularly remarkable for ZnSe surfaces.4.Adsorbed (001) surfaces and interfaces ; depending on the relative energy position between GaAs bands and orbital energies of adsorbed atoms, the spectra intensity has the order of Sb>P>N for GaAs surfaces. When the thickness of hetero-epitaxialized atomic layrs is more than five, the interface spectra show the epsilon_2-derivative shape, which results explain the recent experiments of ZnSe/GaAs interfaces by Yasuda et al.5.(110) nonpolar GaAs surfaces ; reflecting the buckling reconstructions, the optical transitions between the dangling-bond states of As and Ga and the anti-bonding states of Ga-As surface bonds produce the large peaks, which results can be used to determine the adsorption sites on growth. Less