High-Mobility InSe Transistors: The Nature of Charge Transport

InSe is a high-mobility layered semiconductor with mobility being highly sensitive to any surrounding media that could act as a source of extrinsic scattering. However, little effort has been made to understand electronic transport in thin InSe layers with native surface oxide formed spontaneously upon exposure to an ambient environment. Here, we explore the influence of InO_x/InSe interfacial trap states on electronic transport in thin InSe layers. We show that wet oxidation (processed in an ambient environment) causes massive deep-lying band-tail states, through which electrons conduct via 2D variable-range hopping with a short localization length of 1-3 nm. In contrast, a high-quality InO_x/InSe interface can be formed in dry oxidation (processed in pure oxygen), with a low trap density of 10¹² eV^-1 cm^-2. Metal-insulator transition can be thus observed in the gate sweep of the field-effect transistors (FETs), indicative of band transport predominated by extended states above the mobility edge. A room-temperature band mobility of 10³ cm²/V s is obtained. The profound difference in the transport behavior between the wet and dry InSe FETs suggests that fluctuating Coulomb potential arising from trapped charges at the InO_x/InSe interface is the dominant source of disorders in thin InSe channels.