Photo-Induced Structural Changes on Compound Semiconductor Surfaces

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Structural changes and desorption of constituent atoms induced by ns-laser irradiations of cleaved InP (110)-(1x1) surface have been studied by means of scanning tunneling microscopy (STM) and high-sensitivity measurements of desorbed species using femtosecond non-resonant ionization spectroscopy. Atomic imaging of the irradiated surfaces has shown that efficient bond breaking of surface P atoms takes place via electronic processes upon a surface specific transition band on the surface, resulting formation of isolated vacancies at intrinsic P-sites. Repeated irradiations of the surface induces efficient growth of P vacancy-strings elongated selectively along In-P chains ([11^^-0] direction), demonstrating the preferential removal of atoms at neighboring sites of vacancies. The observed formation of vacancy strings with significantly enhanced yields than statistic values is possibly explained by efficient transfer along [11^^-0] direction and condensation of surface excited species. The … More efficiencies of bond breaking at intrinsic lattice sites and sites neighboring vacancies show non-linear increase with increasing excitation intensity, suggesting that non-linear process are included in the bond-breaking.High sensitive measurements of desorbed species from InP (110)-(1x1) and (001)-(4x2) surfaces have shown that laser-induced bond breaking is accompanied with desorption of P, P_2 and In, the relative yields of which are strongly dependent on the surface structure. On the cleaved (110) surface, dominant desorbed species is P atom, yield of which decreases with increasing the number of laser shots on the same spot. Time-of-flight spectra of P-atoms acquired for various excitation intensities were divided into two components, fast and slow components, with the fluence-independent peak flight time and the velocity distribution. The fluence dependences of desorption yields for the fast and slow components are superlinear, and agree with those of the bond breaking efficiencies at intrinsic perfect P sites and at neighboring atomic sites of P-vacancies, respectively. Based on analyses of the non-linear efficiencies, we suggest that two-hole localization is included as a primary step of the electronic bond-breaking on this surface. Less