Accession Number : ADP007908

Title :   Bond-Orbital Model of Two-Hole Laser-Induced Desorption from Gap (110),

Corporate Author : VANDERBILT UNIV NASHVILLE TN DEPT OF PHYSICS AND ASTRONOMY

Personal Author(s) : Haglund, Richard F., Jr. ; Hattori, Ken ; Itoh, Noriaki ; Nakai, Yasuo

Report Date : 22 MAY 1992

Pagination or Media Count : 4

Abstract : The widespread application of lasers in semiconductor processing has produced a voluminous literature on the mechanisms of laser desorption and ablation. There are significant disagreements, however, about the extraordinarily complex physical mechanisms underlying laser desorption and ablation. Here we discuss recent experiments and a model of a particularly simple case: desorption of Ga+ and GaO by selective excitation of a surface electronic state on GaP (110). By choosing the electronic channel leading to desorption, and by monitoring the condition of the surface, one can determine accurately the threshold fluence above which the surface electronic structure is irreversibly altered by laser ablation. Below this threshold, desorption occurs at isolated defect sites and at perfect three-fold coordinated surface sites. This two-hole laser-induced desorption and ablation can be described by a bond-orbital model of electronic structure. Pure crystalline n-type (S-doped) GaP (110) surfaces l0xl5 mm2 were polished and etched according to a standard protocol, then sputter-cleaned and annealed to 500 C in ultrahigh vacuum (10-10 torr). The existence of a contamination-free lxl surface was verified by LEED and Auger spectroscopies. This surface of GaP, shown schematically in Fig. 1, has an unoccupied surface state about 2 eV above the valence-band edge. This surface state was excited by an excimer-pumped dye laser tuned to 600 nm.

Descriptors :   *DESORPTION, *PHOTOCHEMICAL REACTIONS, *LASER PUMPING, *GALLIUM PHOSPHIDES, ABLATION, CHANNELS, CONTAMINATION, DYE LASERS, EDGES, ELECTRONIC STATES, EXCITATION, MODELS, MONITORING, SEMICONDUCTORS, SITES, STANDARDS, STRUCTURES, SURFACES, ULTRAHIGH VACUUM, VALENCE BANDS.

Subject Categories : Physical Chemistry
      Radiation and Nuclear Chemistry

Distribution Statement : APPROVED FOR PUBLIC RELEASE