Surface morphology of polar, semipolar and nonpolar freestanding GaN after chemical etching

Surface etching methods were investigated for the removal of residues of chemical reagents and contaminants from polar (Ga- and N-plane), semipolar (r-plane) and nonpolar (a- and m-plane) freestanding GaN surfaces. Ga-, N-, r- and m-plane were etched in H3PO4, NaOH and (NH4)(2)S solutions. A-plane was treated in the solution of 10 wt% KOH in ethylene glycol (EG) at 80 degrees C. Different surface morphology were obtained and were characterized with atomic force microscope. The typical characteristics for the surface morphologies and interfacial angles in each etched GaN plane may help identify the type of crystal plane conveniently. Ga-polar GaN shows a clear and uniform step structure on surfaces. N-plane presented a step structure with tooth-like terraces. The (2 0 (2) over bar (1) over bar) r-plane, m-plane and a-plane show stripe-like structures, while the (2 0 (2) over bar 1) r-plane is stable and hard to be etched to exhibit step structures. The m-plane facets on a-plane surface caused by the etching method was found and discussed.