Field-Effect Device Using Quasi-Two-Dimensional Electron Gas in Mass-Producible Atomic-Layer-Deposited Al₂O₃/TiO₂ Ultrathin (<10 nm) Film Heterostructures

We report the field-effect transistors using quasi-two-dimensional electron gas generated at an ultrathin (∼10 nm) Al₂O₃/TiO₂ heterostructure interface grown via atomic layer deposition (ALD) on a SiO₂/Si substrate without using a single crystal substrate. The 2DEG at the Al₂O₃/TiO₂ interface originates from oxygen vacancies generated at the surface of the TiO₂ bottom layer during ALD of the Al₂O₃ overlayer. High-density electrons (∼10¹⁴ cm^-2) are confined within a ∼2.2 nm distance from the Al₂O₃/TiO₂ interface, resulting in a high on-current of ∼12 μA/μm. The ultrathin TiO₂ bottom layer is easy to fully deplete, allowing an extremely low off-current, a high on/off current ratio over 10⁸, and a low subthreshold swing of ∼100 mV/decade. Via the implementation of ALD, a mature thin-film process can facilitate mass production as well as three-dimensional integration of the devices.