Low Resistance and Thermally Stable Pt/Ru Ohmic Contacts to p-Type GaN

Abstract

High-quality Pt (20 nm)/Ru (50 nm) Ohmic contacts to surface-treated p-GaN with lowest resistance and thermal stability are reported. The electrical properties and interfacial reactions of the contacts to GaN were investigated using current±voltage, Auger electron spectroscopy, and glancing angle X-ray diffraction measurements. It is shown that the as-deposited contact produces a specific contact resistance of 7.8(AE2.2) Â 10 ± ±4 Wcm 2 , while the contact annealed at 600 C for 2 min yields a resistance of 2.2(AE2.0) Â 10 ± ±6 Wcm 2 . The latter is believed to be the lowest value reported so far for Ohmic contacts to p-GaN. It is further shown that the contacts exhibit excellent thermal stability during annealing at 600 C.Introduction Due to the rapid progress in the growth and processing of GaN-based semiconductors, the electronic and optoelectronic devices have been successfully fabricated on these semiconductors [1,2]. In order to achieve low power loss and allow high temperature operation of such devices, control of the contact metallurgy with low resistance and thermal stability is of great technological importance.For the contacts to p-GaN, despite the problems such as the difficulty in achieving a carrier concentration !10 18 cm ±3 and the absence of appropriate metals having work functions larger than that of p-GaN (6.5 eV) [3], reasonable electrical properties have been achieved [4 to 11]. Most of the contacts studied for p-GaN are Au-based schemes such as Ni/Au [4 to 6], Pt/Au [7], Cr/Au [4], Pd/Au [8], Ni/Pt/Au [9, 10], and Pt/Ni/Au [11]. However, the Au-based contacts generally have poor thermal stability. Several groups have employed Au-free contact schemes such as W [12], WSi x [12], and Ti/Ta/p-GaN[13] to obtain thermally stable and low resistance Ohmic contacts on p-GaN. However, the W-based contacts produced a rather high contact resistance of %10 ±2 Wcm 2 , indicating that these schemes are not suitable for applications on blue LDs. Furthermore, the Ti/Ta/p-GaN contacts were found to experience atmospheric degradation although the contacts had a low contact resistance of 3 Â 10 ±5 Wcm 2 when annealed at 800 C for 20 min in vacuum ( 4 Â 10 ±4 Pa).Native oxide on p-GaN is detrimental to Ohmic properties. It is, therefore, important to remove native oxide thoroughly for achieving low resistance and thermally stable Ohmic contacts. In a previous work [14], we showed that two-step surface treatment is effective in removing native oxide and increasing a near-surface carrier concentration. In this paper, we report on a new metallization scheme for the formation of low resistance and thermally stable Ohmic contacts to the surface treated-p-GaN.

Advances for Enhanced GaN-Based HEMT Devices with p-GaN Gate

“…Usually, surface pretreatment schemes have chemical or physical methods to improve the surface state. Jang et al [39] use two-step processing such as GaN surface, gate metal Pt/Ru deposition before first use of Cl2/Ar/H2 gas mixture of ICP, then boiled with BOE solution for 20 min, lithographically defined image and then treated with BOE for 30s., processing immediately after deposition of metal, without annealing can also contact resistance is 7.8×10 -5 Ω•cm 2 . Chu et al [40] used Be ion implantation method to increase the carrier concentration of p-GaN from 4.1×10 17 cm 3 to 8.1×10 17 cm 3 .…”

Effect of Au distribution in NiO/Au film on the ohmic contact formation to p-type GaN

“…Multilayer metallizations with high work function, including Ni/Au, [3][4][5][6][7] Pt/Au, 8 Pt/Ru, 9 and Pd/Ru, 10 etc., have been widely fabricated as a contact to p-type GaN. The optoelectronic performance of GaN depends on not only the quality of GaN crystals but also the specific contact resistance of metal electrodes to n-and p-type GaN.…”