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

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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 °C molten NaOH+KOH etching whereas N-polar surfaces are chemically active. All the observed flat GaN films grown on (0001) sapphire have Ga polarity. On the contrary, the native flat faces of undoped GaN bulk crystals have N polarity.