Electrical gate control of carrier type of the two-dimensional carrier gas at the FeO<i>_y</i>/SrTiO₃interface and its field-effect-transistor operation

The recently found two-dimensional (2D) hole gas (2DHG), which has ultrahigh mobility up to 24000 cm²/Vs at 4 K, and 2D electron gas (2DEG) formed at the FeO_y/SrTiO₃ (STO) interface are expected to provide a new platform for oxide-based electronics [1]. Here, using a back-gate configuration, we demonstrate for the first time a gate control of the carrier type and mobility of the 2D carrier gas at this interface. The samples were formed by depositing Al (1 nm)/Fe (0.075–0.4 nm) on STO (001) substrates using molecular beam epitaxy. For all the samples, the carrier type was transformed from n-type to p-type with increasing V_G above a threshold value, which varies among samples. This suggests a complicated band structure of this 2D system. Furthermore, at low temperatures (~3.5 K), these devices exhibit excellent transistor features with subthreshold swing values of ~30 mV/dec and on-off ratios of ~10⁷. These results provide insights into the formation mechanism of the 2DHG at the FeO_y/SrTiO₃ interface, as well as highlight the possibility of high-performance field-effect transistors based on the 2D carrier gas on STO substrates.
[1] L. D. Anh et al., Adv. Mater. 32, 1906003 (2020).