InAlGaN/GaN heterostructures with various Al compositions have been grown on sapphire substrate using the metal organic chemical vapour deposition technique. The solid-to-gas phase ratio indicates a high Al incorporation efficiency. Atomic force microscopy reveals a smooth surface with the formation of hexagonal pits. The size and the density of the hexagonal pits increase with increasing Al mole fraction. The Hall effect and the capacitance–voltage (C–V) studies show the formation of a two-dimensional electron gas (2DEG) at the InAlGaN/GaN interface. A relatively higher Hall sheet carrier density compared with the 2DEG density estimated from the C–V profile indicates parallel conduction via the underlying GaN layer. It is observed that the 2DEG density decreases as a function of the Al composition and these results are discussed based on the increasing depth of the hexagonal pit and the background donor density.
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