Subband electron properties of modulation-doped AlxGa1−xN/GaN heterostructures with different barrier thicknesses

Magnetotransport properties of modulation-doped Al0.22Ga0.78N/GaN heterostructures with different barrier thicknesses of 25–100 nm have been investigated in magnetic fields up to 9 T at 1.4 K. Fast Fourier transform has been applied to obtain the subband density and mobility of the two-dimensional electron gas in these heterostructures. High electron density of 1.18×1013 cm−2 and quantum mobility of ∼8200 cm2 V−1 s−1 are obtained when the barrier thickness is 75 nm, which indicates that there exists a critical barrier thickness between 50 and 100 nm in the modulation-doped Al0.22Ga0.78N/GaN heterostructures. We also find that the elastic strain relaxation of the barrier does not significantly enhance the quantum mobilities of the ground subbands, however, it has strong effect on the mobilities of the excited states. The experimental values obtained in this work are useful for the design and optimization AlxGa1−xN/GaN device.