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The etching of n‐ and p‐type normalGaAs in aqueous CrO3‐HF solutions, both under illumination and in the dark, has been studied. On the basis of two ternary composition diagrams, three regions of different etching kinetics can be delineated. These are also regions of different surface morphology after etching. For low false[HFfalse]/false[CrO3false] ratios and false[HFfalse]<10M the etching process is kinetically controlled. The etch rate depends on false[HFfalse] and is independent of false[CrO3false] . High defect sensitivity is obtained in this part of the ternary diagram. For high false[HFfalse]/false[CrO3false] ratios and false[HFfalse]<10M the etching reaction is limited by mass transport of CRVI in solution. Defect sensitivity is poorer in these etchants. For HF concentrations above 10M, a purely chemical etching reaction becomes important and normalGaAs is dissolved with arsine formation. For all solutions, defects in both p‐ and n‐type crystals are found to dissolve more slowly than the surrounding material. Kinetic and morphological results are explained in detail on the basis of a model for electroless etching.

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