Improvement of Ohmic contacts on Ga2O3 through use of ITO-interlayers

Abstract

The use of ITO interlayers between Ga2O3 and Ti/Au metallization is shown to produce Ohmic contacts after annealing in the range of 500–600 °C. Without the ITO, similar anneals do not lead to linear current–voltage characteristics. Transmission line measurements were used to extract the specific contact resistance of the Au/Ti/ITO/Ga2O3 stacks as a function of annealing temperature. Sheet, specific contact, and transfer resistances all decreased sharply from as-deposited values with annealing. The minimum transfer resistance and specific contact resistance of 0.60 Ω mm and 6.3 × 10−5 Ω cm2 were achieved after 600 °C annealing, respectively. The conduction band offset between ITO and Ga2O3 is 0.32 eV and is consistent with the improved electron transport across the heterointerface.

Recent Advances in β-Ga2O3–Metal Contacts

“…The large process window of 900–1150  ° C enables the realization of high-temperature operation. And ITO/Ti/Au electrodes to β-Ga 2 O 3 were also demonstrated by Carey et al [78] in which the sample showed Ohmic behavior with ρ C of 6.3 × 10 − 5 Ω∙cm 2 after annealing. Without the ITO, the same annealing did not deliver linear current–voltage characteristics.…”

“…One is to form an intermediate semiconductor layer (ISL) with low work function by annealing, e.g., Ti 2 O 3 . The other is to insert the deposited ISL between the metal and β-Ga 2 O 3 , which has been intensively studied [76–78]. Compared with the former method, the latter is more favorable to form Ohmic contacts owing to the high carrier concentration of ISL.…”

“…Notably, a bubble on the surface of ITO/Ti/Au contacts was observed while no bubbling on the single ITO layer without metal layer above [78]. It was considered as the result of out-diffusion of oxygen atoms in the ITO layer into the upper metal layers.…”

Device processing and junction formation needs for ultra-high power Ga2O3 electronics

“…It is always challenging to make low resistance Ohmic contacts to wide bandgap semiconductors and generally some form of local doping enhancement by ion implantation, [12,33,34] plasma exposure, [12] or the addition of a low bandgap interlayer (AZO, ITO, InN) [35,36] is used. Ion implantation is still relatively unexplored in Ga 2 O 3 in terms of choice of species, doses, and annealing conditions.…”

Valence and conduction band offsets for sputtered AZO and ITO on (010) (Al0.14Ga0.86)2O3

“…One potential method for reducing the contact resistance is to include a lower gap transparent conducting oxide as an interlayer between the metal and the wide bandgap semiconductor [22][23][24][25][26][27]. The most commonly used TCOs are indium tin oxide (ITO) and aluminum zinc oxide (AZO).…”