Environmental aging of Schottky contacts to n-AlGaN

Gold Schottky contacts to n-AlGaN were fabricated, and the influence of the semiconductor surface preparation on the electrical performance of the diodes was examined. More significantly, the electrical characteristics of the diodes were found to be sensitive to the environment in which they were exposed. Diodes stored in vacuum had stable but poor electrical characteristics, exhibiting the same high reverse leakage currents, low barrier heights, and high ideality factors as the freshly prepared diodes. On the other hand, didoes exposed to air changed over the course of days, in some cases with decreases in the reverse leakage currents by four or more orders of magnitude and increases in the barrier height by 0.3–0.5 eV. Further study of this change in electrical properties showed that the effect was reversible with exposure to ${\mathrm{N}}_{\mathrm{2}}$ gas or vacuum and adequate temperature. In addition, the effect was more pronounced when the metal contact was thin, indicating that diffusion of gases through the metal was significant. This study suggests that nitride semiconductor devices with Schottky barriers to n-AlGaN as components may exhibit improved performance if they are initially stored in air for a few days prior to encapsulation and will also exhibit a pronounced sensitivity to their storage and operational environment if not adequately protected from it.