Polarity determination for GaN films grown on (0001) sapphire and high-pressure-grown GaN single crystals

In order to resolve any doubt in lattice polarity calibrations, a given undoped GaN layer deposited on (0001) sapphire by metalorganic chemical vapor deposition and a given high-pressure-grown GaN single crystal have been studied by three different techniques: Hemispherically scanned x-ray photoelectron diffraction, convergent beam electron diffraction, and chemical etching. We conclude that Ga-polar surfaces are resistant to a 200 degrees C molten NaOH+KOH etching whereas N-polar surfaces are chemically active. All the observed hat GaN films grown on (0001) sapphire have Ca polarity. On the contrary, the native flat faces of undoped GaN bulk crystals have N polarity. (C) 1998 American Institute of Physics.