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Electrical properties of AlxGa1-xN/GaN heterostructures with low Al content

: Köhler, K.; Müller, S.; Waltereit, P.; Pletschen, W.; Polyakov, V.M.; Lim, T.; Kirste, L.; Menner, H.; Brueckner, P.; Ambacher, O.; Buchheim, C.; Goldhahn, R.


Journal of applied physics 109 (2011), No.5, Art. 053705, 5 pp.
ISSN: 0021-8979
ISSN: 1089-7550
Journal Article
Fraunhofer IAF ()

Electrical properties of AlxGa1-xN/GaN heterostructures with an Al content below 15% and carrier concentrations as low as 1.0x1012 cm-2 were investigated by Hall effect measurements and capacitance-voltage profiling. The nominally undoped GaN capped structures were grown by low-pressure metal-organic vapor-phase epitaxy. The threshold voltage of transistor devices follows the trend already found for high Al-containing structures, which are described by a model indicating a surface potential independent of Al content. Photoreflectance spectroscopy confirms the results for as-grown heterostructures. The Hall effect measured on the as-grown samples, however, shows a stronger decrease in carrier concentration than expected from the effect of polarization and constant surface potential. In contrast, Hall effect data determined on samples with Ni Schottky contacts and capacitance-voltage profiling on as-grown samples yield the expected behavior, with surface potentials of 0.86 eV and 0.94 eV, respectively. The inconsistency is eliminated by describing the results of the Hall effect on as-grown samples by a two-carrier model. Self-consistent Schrödinger-Poisson calculations support these considerations if we take into account a transition range at the AlxGa1-xN/GaN interface.