Transport Properties of Two-Dimensional Electron Gases Induced by Spontaneous and Piezoelectric Polarisation in AlGaN/GaN Heterostructures

摘要

We have performed Shubnikov-de Haas (SdH) and Hall effect measurements to investigate the electronic transport properties of polarisation induced 2DEGs in Al_xGa_(1-x)N/GaN heterostructures with alloy compositions between x = 0.10 and 0.35 and sheet carrier concentrations of up to n_s = 1.05 x 10~(13) cm~(-2). From SdH measurements of 2DEGs with sheet carrier concentrations of 2.1 x 10~(12) and 4.6 x 10~(12) cm~(-2), effective electron masses were determined to be 0.24 and 0.207M_0, respectively. In addition, angle resolved SdH measurements were performed to evaluate the effective g-factor from the angle of zero oscillation amplitude. Including the measured electron masses, the g-factors were calculated to be 2.11 and 2.47, respectively. In order to identify the main electron scattering mechanism we determined the ratio between transport- and quantum scattering times as a function of sheet carrier concentration. We observe a significant decrease of the τ_t/τ_q ratio with increasing 2DEG carrier concentration, indicating a transition from a dominant small angle to large angle scattering mechanism when n_s exceeds 7 x 10~(12) cm~(-2).