Key role of initial interface on contact characteristics of Pd/p-GaN

Sequential three-layers of Pd/Pt/Au were deposited on p-GaN by magnetron sputtering under high vacuum (HV, -1.33 x 10-4 Pa) and ultra-high vacuum (UHV, -1.33 x 10-7 Pa) background conditions, respectively, for investigating the electrical contact properties. Linear I-V curves are observed in the samples deposited under the UHV conditions, whereas nonlinear I-V characteristics are obtained in the samples deposited under the HV vacuum. The depth profiles of X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) of the as-deposited samples were probed in detail. It is found that the amounts of O and OH as well as Pd oxide of the sample deposited under the HV background condition are larger than those of the sample deposited under the UHV conditions due to the higher residual gases such as water in the HV chamber. The oxide layer leads to an extra barrier, influencing the electrical characteristics of Pd/Pt/Au/p-GaN contact. This study demonstrates that metal deposition under the UHV environmental conditions can reduce and even prevent formation of oxide on p-GaN surface, and hence favor making a good ohmic contact on p-GaN.

Automated summary

Deposition of Pd/Pt/Au three-layer films on p-GaN under high and ultra-high vacuum conditions was studied to investigate the electrical contact properties. Linear I-V curves were observed in samples deposited under ultra-high vacuum conditions, while nonlinear I-V characteristics were obtained in samples deposited under high vacuum conditions. The study also found that the samples deposited under high vacuum conditions had higher amounts of oxygen and Pd oxide. The oxide layer had an additional influence on the electrical characteristics of the Pd/Pt/Au/p-GaN contact.