The effect of barrier layers on 2D electron effective mass in Al_0.3Ga_0.7N/AlN/GaN heterostructures

The Shubnikov de Haas (SdH) effect measurements have been performed to evaluate the influence of Si₃N₄passivation, a spacer layer, and Si-doped barrier layer on the electronic transport parameters of two-dimensional (2D) electrons in Al_0.3Ga_0.7N/AlN/GaN heterostructures under temperatures from 1.8 K to 40 K and at a magnetic field up to 11 T. The 2D electron effective mass (m*), 2D carrier density (N_2D), the difference between Fermi level and subband energy levels (E_F-E₁), quantum lifetime (τ_q) are determined by analyzing SdH oscillations. Although investigated samples with equal 2D electron density are examined, the effective mass values of 2D electrons are deduced within the range of (0.16 ± 0.005)m₀and (0.23 ± 0.005)m₀. Results reveal that passivation, a spacer layer, and doping affect 2D electron effective mass. Furthermore, the dominant scattering mechanisms that limited electron transport is determined as a long-range scattering for all investigated sample. The results obtained provide information for the high-performance device application of these samples.