Transport properties of 2DEGs in AlGaN/GaN heterostructures: Spin splitting and occupation of higher subbands

To study the electronic transport properties of two-dimensional electron gases confined at the interfaces of AlGaN/GaN heterostructures, Shubnikov-de Haas (SdH) and Hall measurements were performed with structures coveting a wide range of sheet carrier concentrations from 2.25 × 10¹² to 1.83 × 10¹³ cm^-2. For samples with sheet carrier concentrations above 1.7 × 10¹³ cm^-2, the occupation of a second subband was observed. Fourier transformation was used to separate the contributions of both occupied subbands to the electronic transport. Quite similar quantum scattering times and effective masses of the electrons in the first and second subband were determined. In samples with lower sheet carrier concentration traces of a spin splitting could be found by investigating the angle dependence of the SdH-oscillations.