Chemical trend observed in anisotropic surface reflectance spectra of MOVPE by surface photoabsorption

This paper investigates the origin of the surface reflectance spectrum for the group-V-stabilized III–V surface during MOVPE by using surface photoabsorption. A chemical shift is observed for the stoichiometry sensitive peak in the anisotropic spectra of arsenides and phosphides. The peaks observed in the phosphides are located at higher energies than the arsenides, besides the peak in each compound shows a red-shift as the lattice constant increases. To investigate the possibility of the critical point of the bulk energy state appearing in the reflectance spectrum induced by surface modification, the anisotropic spectrum during InAs-on-GaAs heteroepitaxy are measured. One monolayer InAs growth on GaAs results in a drastic change that a peak sign is reversed, accompanied by a red-shift. This can be interpreted by the optical transition change corresponding to the surface conversion from a two-As-layer c(4 × 4)-like surface in GaAs to a one-As-dimer layer having a bond axis perpendicular to the c(4 × 4) As dimer. The contribution of the GaAs bulk electronic state in the reflectance spectrum is not observed. These results support the model that the anisotropic peak originates from an optical transition of the group-V dimer. The anisotropic spectrum measurement also makes it possible to monitor the P/As surface exchange and the As-atom segregation during the InP-on-InAs heteroepitaxy.