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 su rface passivation layer on carrier distributions and mobility in AlxGa1-xN/ GaN heterostructure field-effect-transistor epitaxial layer structures is i nvestigated. Surface chemical treatments are found to exert little influenc e on carrier distribution and mobility. Deposition of a SiO2 surface passiv ation layer is found to induce an increase in electron concentration in the transistor channel and a decrease in mobility. These changes are largely r eversed upon removal of the SiO2 layer by wet etching. These observations a re quantitatively consistent with a shift in Fermi level at the AlxGa1-xN s urface of approximately 1 eV upon deposition of SiO2, indicating that the A lxGa1-xN/SiO2 interface has a different, and possibly much lower, density o f electronic states compared to the AlxGa1-xN free surface. (C) 2001 Americ an Institute of Physics.