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Electronic devices that operate at terahertz frequencies will require new materials that exhibit higher carrier velocities than traditional semiconductors. Calculations show that cadmium arsenide, a 3D topological (Dirac) semimetal, is an excellent candidate for field effect transistors that operate at frequencies above 1 THz. Moreover, such transistors have unique advantages that are enabled by the properties of Dirac electrons. These include predictions of an unprecedented linearity of the transconductance and cutoff frequencies over a large operating range and cutoff frequencies that remain above 1 THz at carrier densities as low as 1011 cm−2. The calculations are underpinned by measurements of devices with cadmium arsenide channels. Extremely low contact resistances (<2 × 10−9 Ω cm2), high electron velocities (>7 × 105 m s−1), and unprecedentedly large current densities (up to 10 A mm−1) are demonstrated. Current modulation (>50%) and transconductance already achieved in the early transistors show the potential for large (>10 ×) improvements by reducing interface trap densities. The results demonstrate the significant potential of topological semimetals for high‐speed transistors operating in the THz regime and open up new opportunities for next‐generation RF circuits. [ABSTRACT FROM AUTHOR]

Cadmium arsenide (Cd3As2) is a three-dimensional Dirac semimetal with many unique electronic properties that are of interest for future device applications. Here, we demonstrate field effect transistors using Cd3As2 as the channel material. We show that current densities exceed 5 A/mm and that very low contact resistances can be achieved even in unoptimized device structures. These properties make Cd3As2 of great interest for future high-speed electronics. We report on the current modulation characteristics of field effect transistors as a function of temperature. At low temperatures, the modulation exceeds 70%. We discuss material and device engineering approaches that can improve the device performance at room temperature. [ABSTRACT FROM AUTHOR]

Integration of ultrathin ferroelectric thin films with semiconductors is of interest for negative capacitance transistors that exhibit internal voltage gain, which may allow for scaling the supply voltage of low power circuits. In this study, BaTiO3 thin films were grown on doped SrTiO3 channels using molecular beam epitaxy. The BaTiO3 films are ferroelectric despite their low thickness (~10 nm). Parallel plate capacitor devices exhibit anti-clockwise hysteresis, and a comparison with reference structures without BaTiO3 shows that the polarization in the BaTiO3 thin films is switchable and controls the charge density in the channel. Field effect transistors were fabricated to study the effect of ferroelectricity on the transistor characteristics. Anti-clockwise hysteresis and a shift in threshold-voltage are observed in the output characteristics of the transistors. These properties make these heterostructures a suitable system for studying negative capacitance effects. [ABSTRACT FROM AUTHOR]