Positron lifetime measurements and Doppler-broadening spectroscopy using slow positrons were combined to investigate open-volume defects created by sawing wafers from GaAs ingots introduced by a diamond saw cutter. The depth distribution represents a large-depth (up to 9.5 μm), wedge-like profile. This was found during step-by-step etching and assembling the respective individual S(E) curves. The depth and the concentration of the defects introduced by the diamond saw depend on the advance of the saw blade. The thermal stability of the detected defects was studied by an isochronal annealing experiment. It was concluded from the positron lifetime measurements and from the Doppler-broadening parameters as well as from the annealing behavior that small vacancy aggregates consisting of at least two vacancies are created by the sawing procedure. More extended defects such as microcracks were analyzed by scanning electron microscopy (SEM). Rutherford-backscattering spectroscopy shows that there is no amorphous material in the near-surface region.
Source: Applied Surface Science