Large-depth defect profiling in GaAs wafers after saw cutting

Positron lifetime measurements and Doppler-broadening spectroscopy using sl ow positrons were combined to investigate open-volume defects created by sa wing wafers from GaAs ingots introduced by a diamond saw cutter. The depth distribution represents a large-depth (up to 9.5 mu m), wedge-like profile. This was found during step-by-step etching and assembling the respective i ndividual S(E) curves, The depth and the concentration of the defects intro duced by the diamond saw depend on the advance of the saw blade. The therma l stability of the detected defects was studied by an isochronal annealing experiment. It was concluded from the positron lifetime measurements and fr om the Doppler-broadening parameters as well as from the annealing behavior that small vacancy aggregates consisting of at least two vacancies are cre ated by the sawing procedure. More extended defects such as microcracks wer e analyzed by scanning electron microscopy (SEM). Rutherford-backscattering spectroscopy shows that there is no amorphous material in the near-surface region. (C) 1999 Elsevier Science B.V. All rights reserved.