Optical response of reconstructed GaP(001) surfaces

GaP(001) surfaces were found to reconstruct with (2X1) or (2X4) symmetry un der surface conditions corresponding to a high or low V/III surface stoichi ometry ratio, respectively. These surface reconstructions, identified by re flection high-energy electron diffraction, have been prepared in a chemical beam epitaxy (CBE) system by varying the sample temperature. Reflectance a nisotropy spectra (RAS) of these surfaces have been taken under both CBE an d metal-organic vapor phase epitaxy conditions. Three different phases of ( 2X4) symmetry have been distinguished according to their characteristic RAS response in agreement with recent theoretical predictions [A.M. Frisch, W. G. Schmidt, J. Bernholc, M. Pristovsek, N. Esser, and W. Richter, Phys. Rev B 60, 2488 (1999)]. For the (2X1) reconstruction a line-shape analysis of the RAS signatures was performed and their temperature shifts have been com pared to the respective shifts of the bulk critical points. These experimen ts indicate the GaP(001)-(2X1) surface dielectric anisotropy originating fr om transitions between bulk states modified by the surface due to band-fold ing effects and anisotropic shifts of the E-1 and E-0' critical point energ ies. [S0163-1829(99)12439-1].