Atomic surface structure of the phosphorous-terminated InP(001) grown by MOVPE

Scanning tunneling microscopy (STM) was used to investigate the microscopic structure of the phosphorous (P)-rich so-called (2×1) reconstruction of InP(001). The samples were homoepitaxially grown in a commercial metal-organic vapor phase epitaxy reactor and then transferred under ultra high vacuum (UHV) conditions into a separate UHV- chamber equipped with low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). After transfer LEED patterns show a (2×1)/(2×2) periodicity with streaks in the [110] direction. STM images display rows in the [110] direction formed by randomly distributed (2×2)/c(2×2)/c(4×2)-like local structures plus many defects. This disorder effect explains the (2×1)-like LEED pattern. The structure of the rows is interpreted in terms of P dimers directed along the [110] direction which are adsorbed on a complete P layer underneath. Prolonged annealing at 350^∘C causes successive desorption of single P dimers as monitored by STM. The LEED pattern remains essentially unaffected and STM images with atomic resolution reveal zig-zag chains in the [110] direction separated by twice the lattice constant. Two adjacent rows can be in or out of phase thus resulting in either p(2×2) or c(4×2) reconstructions. The structure of the rows can be explained in terms of buckled P dimers oriented along the [110] direction on a complete In layer.