Thermally stable Ge/Cu/Ti ohmic contacts to n-type GaN

Abstract

The performance of a novel Ge/Cu/Ti metallization scheme on n-type GaN has been investigated for obtaining thermally and electrically stable low-resistance ohmic contacts. Isochronal (2 min.) anneals in the 600-740°C temperature range and isothermal (690°C) anneals for 2-10 min. duration were performed in inert atmosphere. For the 690°C isothermal schedule, ohmic behavior was observed after annealing for 3 min. or longer with a lowest contact resistivity of 9.1 3 10 À5 V cm 2 after the 10 min. anneal for a net donor doping concentration of 9.2 3 10 17 cm À3 . Mean roughness (R a ) for anneals at 690°C was almost constant at around 5 nm, up to an annealing duration of 10 min., which indicates a good thermal stability of the contact scheme.

Effect of TiN barrier layer in Cu-based ohmic contact of AlGaN/GaN high electron mobility transistor

“…This turns out to be consistent with what Ponon et al found [32]. For convenience of comparison, the properties of several Cu-based ohmic contact stacks are tabulated [23][24][25][26] in table 1 , from which one sees that the ρ C value for the Ti/TiN/Cu being studied here is quite compelling. The leakage current characteristics are presented in figure 6 for different samples.…”

“…As a measure to avoid the Al-Au alloying problems, replacing Au with Cu in the so-called Cu-based contact alternatives has gained popularity [23,24]. Several approaches, such as Ge/Cu/Ti [25], Si/Ti/Al/Cu [23], Ti/Al/Ni/Cu [24], Ti/Al/TiN/Cu [26], have all been investigated. Some of the additional advantages of using Cu are for its lower bulk electrical resistivity (∼1.7 µ Ω cm) [27][28][29] as compared to Au's ∼2.2 µ Ω cm, and higher thermal conductivity (385 vs 310 W m −1 K) beside the lower cost.…”

“…Some of the additional advantages of using Cu are for its lower bulk electrical resistivity (∼1.7 µ Ω cm) [27][28][29] as compared to Au's ∼2.2 µ Ω cm, and higher thermal conductivity (385 vs 310 W m −1 K) beside the lower cost. In order to deter Cu diffusion into the GaN layer, which if undeterred would lead to vacancy-like defects [30], inserting a TiN layer in its proximity has been found to be effective [26], while, further down to the HEMT device at Ti/GaN interface, a nano-sheath of TiN layer was also found to form between Ti and GaN [23,25,31]. Gupta et al has reported that the TiN layer could in fact be single crystalline and exhibit low resistivity at 600 • C. All above findings point favorably to the feasibilities of using TiN as a diffusion barrier to construct a compelling Cu-based ohmic contact stack [28].…”

Low resistance copper-based ohmic contact for AlGaN/GaN high electron mobility transistors

“…[11][12][13] An effective diffusion barrier to Cu is thus required, especially for the ohmic contact. A few ohmic contact structures for GaN devices, such as Si/Ti/Al/Cu/Au, 14 Ge/Cu/Ge, 15 and Ti/Cu/Ge, 16 have been investigated. Although ohmic contacts could be achieved at relatively lower temperatures (<800 C) for these structures, they all suffer from having high contact resistance (r c > Â 10 -5 ohm cm 2 ).…”

Growth evolution and characterization of ultra-thin CoGe2 films synthesized via a catalytic solid–vapour reaction technique

“…Thin lms of metal germanides are of considerable interest to be integrated into very large scale integration (VLSI) circuits as interconnects or ohmic contacts not only for Si and Ge based electronic devices but also for other alternative compound semiconductors. [1][2][3][4][5][6][7][8][9][10][11][12] This is primarily due to their low resistivity, good thermal stability and resistance to oxidation. Among the transition metal germanides, CoGe 2 has been well studied by many researchers for Ge based technology and scarcely for other semiconductor substrates.…”