The surface boundary conditions in GaN/AlGaN/GaN transistor heterostructures

The distribution of electric field in GaN(cap)/AlGaN/GaN(buffer) transistor heterostructures with various AlGaN layer thicknesses (10, 20, and 30 nm) has been studied by contactless electroreflectance and compared with theoretical calculations performed for various positions of the Fermi-level on GaN surface. For the three samples the best agreement between experimental data and theoretical calculations has been found at the same position of the Fermi-level on GaN surface (i.e., 0.55 ± 0.05 eV below the conduction band). It means that the Fermi-level is pinned on GaN surface and this pinning can be treated as the boundary condition for the distribution of polarization-related fields in this heterostructure.