Negative Differential Conductance Due to Extreme Band-Filling in Ionically Gated TiS3 Nanowires

We demonstrate negative differential conductance (NDC), consistent with extreme band filling, in titanium trisulfide (TiS3) nanowire field-effect transistors (FETs) subject to ionic gating. Electronic-structure calculations connect the NDC to the narrow and nonparabolic nature of the conduction band states in TiS3. These exhibit inflection points at relatively low energies, which become accessible when ionic gating induces extreme carrier concentration (∼1020 cm–3). In contrast with the Gunn effect, which requires electron–phonon scattering to transfer electrons between conduction-band valleys to initiate NDC, the mechanism here derives solely from single-carrier, intraband dynamics. As such, the potential should exist to exploit its associated NDC in ultrafast (i.e., terahertz) electronic devices. Since the NDC ultimately results from the heavily d-orbital character of the conduction-band states of TiS3, this phenomenon need not be unique to this material. This should motivate future studies of other materials with similarly strong nonparabolicity.