Etching gratings into an epitaxial AlGaAs layer, as compared to a GaAs layer, is a simple and effective technique for photoelectrochemical (PEC) etching 0.3 μm period gratings. This technique enabled first order gratings for a waveguide outcoupler to be made. It is shown that gratings etch with about three times the ratio of grating depth to total etch when etched in Al0.3Ga0.7As rather than GaAs. The lower hole mobility of AlGaAs was proposed as a possible explanation for this grating resolution improvement.