Investigation of dominance in near-surface region on electrical properties of AlGaN/GaN heterostructures using TLM, XPS, and PEC etching techniques

To investigate how the electrical properties of AlGaN/GaN HEMTs are dominated by the near-surface region, transmission line method and X-ray photoelectron spectroscopy (XPS) measurements were conducted on three samples. There was one sample with poor ohmic properties. The XPS results indicate that the surface-Fermi-level, E FS , position of the poor-ohmic sample was deeper than the others. When a 5 nm thick surface layer was removed by contactless photo-electrochemical etching, E FS shifted to the same position as the others and the contact resistance improved. These results indicate that the control of the near-surface region of AlGaN can be a dominant factor changing the E FS position, which greatly affects the ohmic properties.