Low Resistance Contacts to p-Type GaN

Materials Research Society Symposium Proceedings 468, 427 (1997).

Below is the abstract submitted to the meeting, not the abstract of the published paper:
We report a new metallization process for achieving low resistance ohmic contacts on p-GaN using Pd/Au. The results are compared with those of other high-work-function metals such as Ni/Au and Ti/Au. 2 μm thick p-GaN samples are grown on c-plane sapphire substrates by metalorganic chemical vapor deposition (MOCVD) The carrier concentrations of p-GaN epilayers measured by van der Pauw Hall measurements were in the range of 5 x 10¹⁶/cm³∼ 1 x 10¹⁷/cm³. The p-doped GaN samples were patterned and etched to fabricate mesa structures for transmission line method (TLM) measurement. The mesas were separated using chemically-assisted ion beam etching (CAIBE) with Cl₂ gas. The dimension of rectangular pads was 200 μm wide and 100 _μm long. The gaps between the contact pads were increased from 5 to 30 um with 5 μm increment. All metal contacts were deposited by e-beam evaporation. I-V characteristics of metal contacts were measured before and after rapid thermal annealing (RTA). The Pd/Au contacts showed linear ohmic characteristics between -0.1 mA and 0.1 mA ranges while the slope of the I-V curve was slightly increased beyond the linear range. The calculated specific contact resistance of the Pd/Au contact after annealing at 500°ree;C for 30 second was 2.7 x 10^-2Ωcm². This is almost 2 orders of magnitude lower than those of Ni/Au and Pt/Au contacts whose specific contact resistances were in the range of 2∼20 Ω-cm². Keeping in mind of a low doping level and a very high sheet resistance (∼1.5 x 10⁸|Omega) of the test samples, the Pd/Au is considered as a promising candidate for low resistance ohmic contact to p-GaN.

This paper is part of Gallium Nitride and Related Materials II

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