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

Al(x)Ga(1-x)N/GaN heterostructure field-effect transistors with different Al concentrations (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 Poisson equations with the proper boundary conditions. The total (piezoelectric and spontaneous) polarization has been included as a fitting parameter in the 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 of such dependence, and the magnitude of the total polarization field are lower than the predicted ones using the usually accepted values of the piezoelectric and spontaneous polarization coefficients. (C) 1999 American Institute of Physics. [S0003-6951(99)00642-7].