Polarization fields determination in AlGaN/GaN heterostructure field-effect transistors from charge control analysis

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 Angstrom) have been fabricated and characterized. Experimental results were analyzed by using a self-consistent solution of the Schrodinger and Poisso n equations with the proper boundary conditions. The total (piezoelectric a nd spontaneous) polarization has been included as a fitting parameter in th e self-consistent calculations. From the analysis of the transistor charge- control experimental data, a linear increase of the polarization field with the Al concentration has been found. Our results indicate that the slope o f such dependence, and the magnitude of the total polarization field are lo wer than the predicted ones using the usually accepted values of the piezoe lectric and spontaneous polarization coefficients. (C) 1999 American Instit ute of Physics. [S0003-6951(99)00642-7].