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- ItemRefractory metal-based ohmic contacts on β-Ga2O3 using TiW(Melville, NY : AIP Publ., 2022) Tetzner, Kornelius; Schewski, Robert; Popp, Andreas; Anooz, Saud Bin; Chou, Ta-Shun; Ostermay, Ina; Kirmse, Holm; Würfl, JoachimThe present work investigates the use of the refractory metal alloy TiW as a possible candidate for the realization of ohmic contacts to the ultrawide bandgap semiconductor β-Ga2O3. Ohmic contact properties were analyzed by transfer length measurements of TiW contacts annealed at temperatures between 400 and 900 °C. Optimum contact properties with a contact resistance down to 1.5 × 10-5 ω cm2 were achieved after annealing at 700 °C in nitrogen on highly doped β-Ga2O3. However, a significant contact resistance increase was observed at annealing temperatures above 700 °C. Cross-sectional analyses of the contacts using scanning transmission electron microscopy revealed the formation of a TiOx interfacial layer of 3-5 nm between TiW and β-Ga2O3. This interlayer features an amorphous structure and most probably possesses a high amount of vacancies and/or Ga impurities supporting charge carrier injection. Upon annealing at temperatures of 900 °C, the interlayer increases in thickness up to 15 nm, featuring crystalline-like properties, suggesting the formation of rutile TiO2. Although severe morphological changes at higher annealing temperatures were also verified by atomic force microscopy, the root cause for the contact resistance increase is attributed to the structural changes in thickness and crystallinity of the interfacial layer.
- ItemRecent progress in the development of β-Ga2O3 scintillator crystals grown by the Czochralski method(Washington, DC : OSA, 2021) Drozdowski, Winicjusz; Makowski, Michał; Witkowski, Marcin E.; Wojtowicz, Andrzej J.; Irmscher, Klaus; Schewski, Robert; Galazka, ZbigniewA high-quality bulk single crystal of β-Ga2O3 has been grown by the Czochralski method and its basic scintillation characteristics (light yield, energy resolution, proportionality, and scintillation decay times) have been investigated. All the samples cut from the crystal show promising scintillation yields between 8400 and 8920 ph/MeV, which is a noticeable step forward compared to previous studies. The remaining parameters, i.e. the energy resolution slightly above 10% (at 662 keV) and the scintillation mean decay time just under 1 μs, are at the same level as we have formerly recognized for β-Ga2O3. The proportionality of yield seems not to deviate from standards determined by other commercial scintillators.