Abstract
Preserving a contamination-free metal-semiconductor interface in β-Ga2O3 is critical to achieve consistently low resistance ( < 1 Ω-mm) ohmic contacts. Here, we report a scanning transmission electron microscopy study on the variation in Ti/Au ohmic contact quality to (010) β-Ga2O3 in a conventional lift-off vs a metal-first process. We observe a thin ∼1 nm carbon barrier between the Ti and Ga2O3 in a non-conductive contact fabricated by a conventional lift-off process, which we attribute to photoresist residue, not previously detected by x-ray photoelectron spectroscopy due to the thinness and patchy coverage of the carbon layer, as well as roughness of the Ga2O3 surface. This thin carbon barrier is confirmed by electron energy loss spectroscopy and atomic force microscopy-infrared spectroscopy. We believe that the presence of the thin and patchy carbon layer leads to the highly inconsistent contact behavior in previous reports on non-alloyed contacts. Adventitious carbon is also observed in a conductive ohmic contact metal-first processing on an as-grown sample. We find that a five minute active oxygen descum is sufficient to remove this carbon on as-grown samples, further improving the ohmic behavior and reducing the contact resistance Rc to 0.06 Ω-mm. We also show that an hour long UV-ozone treatment of the Ga2O3 surface can eliminate carbon residue from the lift-off processing, resulting in a low Rc of 0.05 Ω-mm.
| Original language | English |
|---|---|
| Article number | 061122 |
| Journal | APL Materials |
| Volume | 13 |
| Issue number | 6 |
| DOIs | |
| State | Published - Jun 1 2025 |
| Externally published | Yes |
Funding
This work was in part supported by ACCESS, an AFOSR Center of Excellence (Grant No. FA9550-18-1-0526), and in part by SUPREME, one of seven centers in JUMP 2.0, a Semiconductor Research Corporation (SRC) program sponsored by DARPA. The device fabrication was performed in part at the Cornell Nanoscale Facility, a NNCI member supported by NSF Grant No. NNCI-2025233. This work made use of the electron microscopy facility of the Cornell Center for Materials Research (CCMR) with support from the National Science Foundation Materials Research Science and Engineering Centers (MRSEC) program (Grant No. DMR1719875). The Thermo Fisher Spectra 300 X-CFEG was acquired with support from PARADIM, an NSF MIP (Grant No. DMR-2039380) and Cornell University. N.P. acknowledges support from the National Science Foundation Graduate Research Fellowship under Grant No. DGE2139899. N.P. thanks Lopa Bhatt for helpful conversations. C.A.G. acknowledges support from the National Defense Science and Engineering (NDSEG) Fellowship. The Bruker Anasys nanoIR3-s AFM-IR system utilized in this work was acquired with support from the M. J. Murdock Charitable Trust via Award No. 202014907. The system is located in the Boise State University Surface Science Laboratory (SSL), which is part of the FaCT Core Facility, RRID: SCR 024733, which receives support from the National Institutes of Health under the Institutional Development Awards Program of the National Institute of General Medical Sciences via Grant Nos. P20GM148321 and P20GM103408, the former of which also partially supports co-authors C.M.E. and P.H.D. P.H.D. thanks Douglas A. Davis for helpful conversations.