Accelerated Aging Stability of β-Ga₂O₃–Titanium/Gold Ohmic Interfaces

Abstract

Stable ohmic contacts are critical to enable efficient operation of high-voltage electronic devices using ultrawide bandgap semiconductors.Here we perform, for the first time, thermally accelerated aging of Ti/Au ohmic interfaces to (010) β-Ga 2 O 3 . We find that a heavily doped semiconductor, doped n-type by Si-ion implantation, treated with reactive ion etch (RIE), results in a low specific contact resistance of ∼10 −5 Ω cm 2 that is stable upon accelerated thermal aging at 300 °C for 108 h. The low resistance interface is due to thermionic field emission of electrons over an inhomogeneous barrier. Scanning/transmission electron microscopy indicates that the multi-layered structure and elemental distribution across the contact interface, formed during a 1 min 470 °C post-metallization anneal, do not change noticeably over the aging period. A ∼1 nm interfacial layer is observed by high-resolution microscopy at the Ti−TiO x /Ga 2 O 3 interface on all samples exposed to RIE, which may contribute to their excellent stability. In addition, longer-range facet-like interfacial features are observed, which may contribute to the inhomogeneous barrier. In contrast, Ti/Au junctions to moderately doped (010) Ga 2 O 3 made with no RIE treatment exhibit a high contact resistance that increases upon accelerated aging, along with a partially latticematched interface. The methods used here to understand the process, structure, and electrical property relationships for Ti/Au contact interfaces to β-Ga 2 O 3 can be applied to assess and tune the stability of a variety of other oxide−semiconductor interfaces.

β-Ga2O3 material properties, growth technologies, and devices: a review

“…Si-ion implantation doping and regrowth have been utilized to form n + -Ga 2 O 3 ohmic regions [52,59,60]. The post-metallization annealing provides short-range intermixing of Ti and Ga 2 O 3 at the interface, resulting in further reduction in contact resistance and improvement in reliability and endurance [61][62][63]. The routine process developed in the author's group based on the Si-ion implantation doping described in Section 5.1.1 and postmetallization annealing can provide a low specific contact resistance of less than 1×10 −5 cm 2 .…”

Bidirectional Control of the Band Bending at the (2̅01) and (010) Surfaces of β-Ga2O3 Using Aryldiazonium Ion and Phosphonic Acid Grafting

“…Interestingly, β-Ga 2 O 3 appears to show a fundamental difference to other TSOs in that its surfaces usually exhibit upward band bending and near-surface electron depletion, although this is sensitive to their environmental and chemical processing histories. − This is in contrast to the downward band bending and electron accumulation commonly observed at ZnO, , CdO, SnO 2 , and In 2 O 3 surfaces . This difference is surprising given that, on exposure to the atmosphere, the surfaces of β-Ga 2 O 3 and those of other TSOs are similarly terminated with an outer layer of hydroxyl groups formed from the dissociative adsorption of water. − Upward surface band bending allows the relatively facile formation of highly rectifying Schottky contacts (SCs) to β-Ga 2 O 3 , , but makes the formation of high-quality ohmic contacts more difficult, , and may also impact other applications such as gas/biosensing and catalysis, for which a high near-surface electron density is beneficial.…”

“…14 This difference is surprising given that, on exposure to the atmosphere, the surfaces of β-Ga 2 O 3 and those of other TSOs are similarly terminated with an outer layer of hydroxyl groups formed from the dissociative adsorption of water. 15−19 Upward surface band bending allows the relatively facile formation of highly rectifying Schottky contacts (SCs) to β-Ga 2 O 3 , 20,21 contacts more difficult, 22,23 and may also impact other applications such as gas/biosensing and catalysis, for which a high near-surface electron density is beneficial.…”

Nanoscale Characterization of Chemical and Structural Properties of the Au/(100) β-Ga2O3 Interface

“…As established here and by other authors, metal–semiconductor interfaces often exhibit reactions either at room temperature or at elevated temperatures, and currently, the stability of various commonly employed metallizations to β-Ga 2 O 3 is not understood. There is ample evidence in the literature of room temperature (Cr, Ti, − and now Au) and elevated temperature (Pd, Ni , ) reactions of common metallizations to β-Ga 2 O 3 . However, there is no report of a Ni/β-Ga 2 O 3 reaction for Ni deposited at room temperature.…”