Boiling an undoped LEC semi-insulating GaAs wafer in deionized water forms an oxide film on the wafer which gives a visual representation of the defects in the wafer. This preferential oxidation of GaAs was found to be promoted by photons. These findings suggest that the density of photogenerated holes, which play the leading role in oxidation, should be high around defects, because defects, such as dislocations and lineage, can absorb hole traps. The oxide film is thus thick in the vicinity of a defect and thinner away from it. The defect pattern can be extinguished by carrier doping prior to boiling.
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