king-mrssp-468-421

Data for reference king-mrssp-468-421

Temperature Behavior of Pt/Au Ohmic Contacts to p-GaN

D.J. King, L. Zhang, J.C. Ramer, S.D. Hersee, L.F. Lester

Materials Research Society Symposium Proceedings 468, 421 (1997).

Below is the abstract submitted to the meeting, not the abstract of the published paper:
A Pt/Au metallization to Mg-doped p-GaN grown by MOCVD has been studied using circular contact test structures to avoid the need for etching isolation. An NH₄OH:DI solution was used as a premetallization surface treatment, and Pt/Au, 500/2000 Å, was deposited by electron beam evaporation onto the p-GaN. Before metallization, samples were given a p-dopant activation anneal of 700°ree;C for 20 min. by rapid thermal anneal (RTA) to drive out compensating hydrogen, and a second, alloying anneal at 750°ree;C after metallization. The specific contact resistance, r_c, for these contacts varies from 2.0-8.0x10^-3 Ω-cm² when the electrical measurements are taken at room temperature. Studies of the electrical properties of the Pt/Au contacts after fabrication reveal that the sheet resistance and the r_c show a temperature dependence, which could prove important for high temperature device applications. With increasing temperature, it is found that the sheet resistance and r_c decrease and that the I-V linearity of the metal contacts improves significantly. From 25°ree;C to 285°ree;C, the sheet resistance decreases by an order of magnitude, from 64,000 to 6,070 Ω/square. Below 245°ree;C, the I-V curve of the contact has a slight kink near the origin, but at 245°ree;C and above, the I-V is linear. A specific contact resistance of 6.6x10^-4 Ω-cm² for the Pt/Au is obtained at a temperature of 285°ree;C. This result is the lowest reported r_c for ohmic contacts to p-GaN. The significant decrease in the r_c at higher temperatures is attributed to an increased hole concentration which results in more efficient tunneling through the voltage barrier at the Pt/GaN interface. The improvement in I-V linearity with temperature indicates a transition from current flow that has a significant thermionic component at low T to one that is dominated by tunneling at high T.

This paper is part of Gallium Nitride and Related Materials II

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