Influence of surface processing and passivation on carrier concentrations and transport properties in AlGaN/GaN heterostructures

The influence of surface chemical treatments and of deposition of a SiO₂ surface passivation layer on carrier distributions and mobility in Al_xGa_1-xN/GaN heterostructure field-effect-transistor epitaxial layer structures is investigated. Surface chemical treatments are found to exert little influence on carrier distribution and mobility. Deposition of a SiO₂ surface passivation layer is found to induce an increase in electron concentration in the transistor channel and a decrease in mobility. These changes are largely reversed upon removal of the SiO₂ layer by wet etching. These observations are quantitatively consistent with a shift in Fermi level at the Al_xGa_1-xN surface of approximately 1 eV upon deposition of SiO₂, indicating that the Al_xGa_1-xN/SiO₂ interface has a different, and possibly much lower, density of electronic states compared to the Al_xGa_1-xN free surface. © 2001 American Institute of Physics.