A PHOTOEMISSION-STUDY OF COHERENTLY STRAINED INXGA1-XAS/INP(100)

Coherently strained 8 nm thick films of InO.30Ga0.70As (tensional strain = 1.7%) and In0.75Ga0.25Aa (compressional strain = -1.5%) were grown by molecular beam epitaxy on InP(100), on which In0.53Ga0.47As is the lattice-matched composition. Samples were studied with synchrotron-radiation photoemission measurements of the d-core levels of each ion. The results show (i) shifts of the core-level energies of surface ions consistent with previous results on As-rich (100) III-V surfaces, and (ii) significant intrinsic broadening of the core levels, especially the In 4d. Comparison of the two compositions showed (i) an increase in the binding energies of the Ga 3d and In 4d peak by 0.17 eV at the higher In concentration, and (ii) a constant separation of the In 4d from the Ga 3d of (1.80 +/- 0.03) eV. A rigid-ion model of the alloy-semiconductor surface successfully predicts the observed halfwidths. The model also predicts that surface rumpling occurs in the As-terminated cation layer: The In ions are pushed out beyond the Ga ions. This rumpling has the effect of increasing the shift of the 4d-core binding energy for the "surface" In atoms.