ITO Schottky Diode wth Record fT Beyond 400 GHz: Exploring Thickness Depdendant Film Property and Novel Heterogeneous Design

We report the discovery of a strong thickness dependent electrical property of ultra-thin indium-tin-oxide (ITO) film when ITO thickness (TITO) enters sub-10 nm regime: a transition from metal-like to SEMI-like. We further propose a heterogeneous structure design in Schottky diodes to make full use of such discovery so that thin SEMI-like ITO was used for Schottky barrier formation and thick metal-like ITO was used to minimize the contact resistance. Together with the optimization of the O2 flow during sputtering deposition, breakthrough device performance was realized, including a rectifying ratio of 5 orders and a cut-off frequency (fT) of 422 GHz in the device with the shortest diode length (LD) of 35 nm. The device also exhibits outstanding ION of 116.6 $\mu$A/$\mu$m, low ideality factor of 1.06, as well as a promising efficient energy harvesting capability with a current responsivity of 18 A/W.