V/Al/Pt/Au Ohmic contact to n-AlGaN/GaN heterostructures

Abstract

A study of V/Al/Pt/Au and Ti/Al/Pt/Au contacts to n-Al0.3Ga0.7N/GaN heterostructures is presented. Vanadium was chosen as a potential replacement for Ti because V is expected to form a thermally stable nitride with a low work function. Low-resistance Ohmic contacts are achieved with V/Al/Pt/Au layers after annealing at 650 °C, which represents a decrease of 150 °C compared to the Ti/Al/Pt/Au counterpart. This contact exhibits two orders of magnitude lower specific contact resistance compared to the Ti/Al/Pt/Au contacts studied in this work when annealed at temperatures less than 800 °C, although the specific contact resistance of the Ti/Al/Pt/Au contacts is lower when annealed at higher temperatures. A contact resistance and specific contact resistance of 0.8±0.1 Ω mm and (1.4±0.3)×10−5 Ω cm2, respectively, are obtained after annealing at 650 °C for 45 s.

Electrical and structural properties of low-resistance Ti/Al/Re/Au ohmic contacts to n-type GaN

“…For example, bilayer metal films, such as Ni/Au, Ti/Au, Pd/Au, Pt/Au, and Mo/Au, which are resistant to oxidation, were placed on the top of the Ti/Al contacts to prevent the oxidation of the contacts during alloying. [10][11][12][13][14][15][16][17] In this work, refractory metal Re was introduced as a capping layer because it is thermally stable. 18 In other words, the Re/Au capping layer is expected to protect the Ti/Al layer against oxidation and, consequently, to improve the ohmic property of the Ti/Al contact.…”

Improved Long-Term Thermal Stability At 350°C Of TiB2–Based Ohmic Contacts On AlGaN/GaN High Electron Mobility Transistors

“…The most commonly used metallization scheme for source/ drain contacts on these HEMTs is Ti/Al, with overlayers of Pt, Ni or Ti and then a layer of Au to reduce oxidation problems and lower the sheet resistance of the contact stack. [11][12][13][14][15][16][17][18][19][20][21][22][23] These contacts produce low specific contact resistances when annealed in the 750-900°C range but there are concerns about the long-term stability during high temperature operation, in part because if the metal layers begin to intermix, a low melting temperature AlAu 4 phase may form that can lead to contact shorting at small electrode separations. 19 One possible solution is to use a very high melting point diffusion barrier in place of the Pt, Ni or Ti in the contact stack.…”

Chemical structure of vanadium-based contact formation on n-AlN

“…Vanadium-based contacts involving rapid thermal annealing (RTA) were first used on nAl0.3Ga0.7N, and it was found that optimal contact formation occurred at less severe conditions (i.e., lower processing temperatures) compared to Ti-based contacts [6]. However, it was found that, with increasing Al content in the alloy, the optimal RTA temperature had to be increased for optimal specific contact resistivity [7].…”

“…To understand the origin of this feature, a sum spectrum was computed using the VN (mod.) and V metal reference spectra and suitable weight factors to describe the RTA data 6 (shown in Fig. 2, top portion).…”