We present a set of experiments which systematically clarifies the enhancement of photoelectrochemical (PEC) etching due to the mole fraction of aluminum in AlxGa1-xAs. The spatial resolution of gratings etched in Al0.3Ga0.7As is as much as three times greater than the spatial resolution of gratings etched in GaAs, so that the smallest practical grating period is about 0.3 μm, as compared with about 0.7 μm using previous techniques. This technique enabled PEC fabrication of first order gratings for waveguide outcouplers. The lower hole mobility of Al xGa1-xAs is proposed as a possible explanation for this grating resolution improvement.© 1995 American Institute of Physics.