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

Magnetotransport properties of modulation-doped Al0.22Ga0.78N/GaN heterostr uctures with different barrier thicknesses of 25-100 nm have been investiga ted 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 e lectron gas in these heterostructures. High electron density of 1.18x10(13) cm(-2) and quantum mobility of similar to 8200 cm(2) V-1 s(-1) are obtaine d 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 Al 0.22Ga0.78N/GaN heterostructures. We also find that the elastic strain rela xation 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 usef ul for the design and optimization AlxGa1-xN/GaN device. (C) 2001 American Institute of Physics.