Analysis of Leakage Current at Pd/AlGaN Schottky Barriers Formed on GaN Free-Standing Substrates

Analytical solutions based on the thin surface barrier (TSB) model were utilized to reproduce the measured current--voltage characteristics of Pd/unintentionally doped Al 0.08 Ga 0.92 N/compositionally graded AlGaN/n-GaN Schottky barrier diodes (SBDs) formed on GaN free-standing substrates. The TSB thickness ($D$) and the Schottky barrier height were used as fitting parameters, while the measured surface concentration of shallow donors was used as a constant. Since the resultant $D$ was close to the value determined from the oxygen concentration profiles, the surface oxygen was concluded to be deeply-involved in the TSB formation.