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The C-V and I-V characteristics of the Ni/Al0.26Ga0.74N/GaN and Ni/Al0.20Ga0.80N/GaN Schottky diodes were measured for determination of structures electrical parameters as well as influence of metal-pad electrode to Schottky barrier height evaluation. From measured C-V curves, the sheet charge density of carriers in the channel was determined. The I-V characteristics were measured in the temperature range from 298 to 473 K and analyzed considering different current-transport mechanisms. The Schottky barrier height of both investigated structures with metal-pad show equal value ~1.3 eV at 298 K, while for structures without metal-pad the barrier height of the Schottky diodes was 2.23 eV and 2.02 eV for Ni/Al0.26Ga0.74N/GaN and Ni/Al0.20Gain0.80N/GaN sample, respectively. This results indicate the presence of excess oxide layer under Schottky contact at AlGaN surface during the contact processing.