Polarization field determination in AlGaN/GaN HFETs

AlxGa1-xN/GaN heterostructure field effect transistors with different Al co ncentrations (0.15 < x 0.25) and barrier widths (150 Angstrom < W-B < 350 A ngstrom) have been fabricated and characterized. The experimental results w ere analyzed by using a self-consistent solution of-the Schrodinger and Poi sson equations with the proper boundary conditions. The total (piezoelectri c and spontaneous) polarization has been included as a fitting parameter in the self-consistent calculations. Comparing simula tion results with exper imental data, a linear increase of the polarization field with the Al conce ntration has been found. Our results indicate that the slope of such depend ence and the magnitude of the total polarization field are lower than the p redicted ones using the usually accepted values of the piezoelectric and sp ontaneous polarization coefficients.