Materials based on Al 1−x In x N offer much potential for the fabrication of high electron mobility transistors (HEMT) because the spontaneous polarization difference between InAlN and GaN should give rise to positive polarization charge at the AlInN/GaN interface [1] . Furthermore, electrons in nearby regions should compensate for this polarization charge, leading to the formation of twodimensional electron gas (2DEG). AlInN/GaN HEMT heterostructures grown on sapphire substrates have been

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... ted with a 2DEG density of ~2.6x10 13 cm -2 [2]. The position of the 2DEG layer has yet to be determined and structural analysis is lacking. In this study, we have investigated the microstructure and electrostatic potential profiles across Al 0.85 In 0.15 N/AlN/GaN HEMT heterostructures. These materials were grown in an AIXTRON 200/4 RF-S metalorganic vaporphase epitaxy (MOVPE) system on 2-in. c-plane sapphire substrates. A JEOL 4000EX was used for microstructural analysis, a JEOL 2010 was used for small-probe microanalysis, and a Philips-FEI CM200 was used for holographic studies.