Magnetotransport properties of a polarization-doped three-dimensional   electron slab
  We present evidence of strong Shubnikov-de-Haas magnetoresistance oscillations in a polarization-doped degenerate three-dimensional electron slab in an Al$_{x}$Ga$_{1-x}$N semiconductor system. The degenerate free carriers are generated by a novel technique by grading a polar alloy semiconductor with spatially changing polarization. Analysis of the magnetotransport data enables us to extract an effective mass of $m^{\star}=0.19 m_{0}$ and a quantum scattering time of $\tau_{q}= 0.3 ps$. Analysis of scattering processes helps us extract an alloy scattering parameter for the Al$_{x}$Ga$_{1-x}$N material system to be $V_{0}=1.8eV$. 
D. Jena, S. Heikman, J. S. Speck, A. C. Gossard, U. K. Mishra, A.   Link, and O. Ambacher