Slicing of GaAs wafers from ingots causes a damage layer whichmust be completely removed by polishing. For this purpose anon-destructive control of the machining process is very desirable.Laser-induced surface acoustic waves are demonstrated to be apromising method to characterize the state of the surface. Thedispersion of this wave mode has been used as a measure of thethickness of the damage layer The investigations were performed onwafers which were stepwise polished to remove the damage layer. Inthis way the damage layer was found to have a thickness of about 10 μm. This result is in good agreement with investigations performedwith positron annihilation. The damage layer was found to have aconsiderably lower elastic modulus (by up to about 18/100) than thebulk material of GaAs. With increasing polishing depth the modulus ofthe damage layer approaches that of the bulk material. The elasticmodulus allows us to estimate the defect volume in the damage layerby applying a theory of heterogeneous materials. A defect volumefraction of 0.48/100 was estimated for the as-sawn state of the waferIt decreases to 0.05/100 for a polishing depth of 6.5 μm and goes tozero at a depth of 10 μm.
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