Modulation of mobility in homoepitaxially‐grown AlGaN/GaN heterostructures

Abstract

AbstractWe report on the growth of Al0.25Ga0.75N/GaN heterostructures on low dislocation density semi‐insulating c‐axis GaN substrates. Room temperature Hall mobilities up to 1805 cm2/Vs at sheet carrier densities of 0.77x1013 cm–2 have been measured. By varying the GaN buffer layer thickness in these homoepitaxially‐grown Al0.25Ga0.75N/GaN heterostructures, we observed a buffer‐induced modulation of the room temperature 2DEG sheet carrier densities and Hall mobilities. The increase in sheet carrier density and corresponding decrease in mobility as the GaN buffer layer thickness is reduced below 0.75 μm is related to the presence of Si impurities at the bulk GaN substrate/epitaxial interface. Capacitance‐voltage measurements and SIMS analysis confirm the presence of Si impurities at the surface prior to and after epitaxial growth. The factor of 2 reduction in the room temperature mobility is consistent with a predicted theoretical mobility reduction based on intersubband scattering. We have also been able to separate the contributions to the 2DEG carrier density from the ionized donors and the polarization field; the magnitude of each is ∼5x1012 cm–2. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)