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HL: Fachverband Halbleiterphysik

HL 33: Poster Session III

HL 33.9: Poster

Mittwoch, 14. März 2018, 17:30–19:30, Poster F

Transport properties and structural characteristics of thin AlGaN/(AlN)/GaN heterostructures and their built-in 2D electron gases — •Dennis Mauch, Heiko Bremers, Uwe Rossow, and Andreas Hangleiter — Institut für Angewandte Physik, TU Braunschweig, Germany

We present transport properties of ultrathin AlGaN/AlN/GaN heterostructures, grown on c-oriented sapphire substrates in our commercial MOVPE system. These heterostructures form a two-dimensional electron gas (2DEG) with high mobilities, showing values exceeding 15000 cm²/Vs at 4K with observed sheet carrier densities ranging from 3−12× 10¹² cm⁻². As a consequence of the noncentrosymmetry of the wurtzite structure in group-III nitrides, a large spontaneous polarization is oriented along the hexagonal c-axis. In addition, group-III nitrides are highly piezoelectric. Hence, in AlGaN/GaN heterostructures, where the AlGaN layer is grown pseudomorphically on top of GaN, strain leads to piezoelectric polarization in this AlGaN epitaxial layer. The electric field, induced by the polarization discontinuity at the heterointerface, then gives rise to the formation of a 2DEG ("polarization doping"). We also investigated the influence of an additional AlN interlayer at the AlGaN/GaN interface in order to reduce alloy disorder scattering and thus to reach higher 2DEG mobilities. The transport properties were analysed via Hall effect measurements at room temperature and also by Shubnikov-de Haas measurements at 4K. The structural details were obtained from high-resolution X-ray diffraction and X-ray reflectivity.