ARSENIC BEAM FROM A MBE SOURCE CHARACTERIZED BY FEMTOSECOND LASER SPECTROSCOPY

We present measurements allowing a characterization of arsenic beams f rom commercial molecular beam epitaxy (MBE) sources. A combination of multiphoton ionization with fs laser pulses and time-of-flight mass sp ectrometry allows a determination to be made of the size distribution of neutral particles in the arsenic beam. We find that arsenic tetrame rs As-4 are the constituents of a molecular beam. Of importance are pa rameters such as laser intensity, pulse duration, and laser wavelength for a quantitative characterization and thereby improvement of MBE so urces. This would help to optimize the epitaxial growth process. We de monstrate that nonresonant multiphoton ionization (MPI) by fs laser pu lses leads to detection of the parent molecule, whereas nonresonant MP I with ns laser pulses leads to strong fragmentation.