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Register a new userElectric-Field Modulation of Thermopower for the KTaO3 Field Effect Transistors
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We show herein fabrication and field-modulated thermopower for KTaO3 single-crystal based field-effect transistors (FETs). The KTaO3 FET exhibits field effect mobility of ~8 cm2/Vs, which is ~4 times larger than that of SrTiO3 FETs. The thermopower of the KTaO3 FET decreased from 600 to 220 microV/K by the application of gate electric field up to 1.5 MV/cm, ~400 microV/K below that of an SrTiO3 FET, clearly reflecting the smaller carrier effective mass of KTaO3.
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An n-channel accumulation-type field effect transistor (FET) has been fabricated utilizing a KTaO3 single crystal as an active element and a sputtered amorphous Al2O3 film as a gate insulator. The device demonstrated an ON/OFF ratio of 10^4 and a field effect mobility of 0.4cm^2/Vs at room temperature, both of which are much better than those of the SrTiO3 FETs reported previously. The field effect mobility was almost temperature independent down to 200K. Our results indicate that the Al2O3 / KTaO3 interface is worthy of further investigations as an alternative system of future oxide electronics.
To clarify the electronic density of states (DOS) around the conduction band bottom for state of the art transparent amorphous oxide semiconductors (TAOSs), InGaZnO4 and In2MgO4, we fabricated TAOS-based transparent thin film transistors (TTFTs) and measured their gate voltage dependence of thermopower (S). TAOS-based TTFTs exhibit an unusual S behavior. The |S|-value abruptly increases, but then gradually decreases as Vg increases, clearly suggesting the anti-parabolic shaped DOS is hybridized with the original parabolic shaped DOS around the conduction band bottom.
The spin field effect transistor envisioned by Datta and Das opens a gateway to spin information processing. Although the coherent manipulation of electron spins in semiconductors is now possible, the realization of a functional spin field effect transistor for information processing has yet to be achieved, owing to several fundamental challenges such as the low spin-injection efficiency due to resistance mismatch, spin relaxation, and the spread of spin precession angles. Alternative spin transistor designs have therefore been proposed, but these differ from the field effect transistor concept and require the use of optical or magnetic elements, which pose difficulties for the incorporation into integrated circuits. Here, we present an all-electric and all-semiconductor spin field effect transistor, in which these obstacles are overcome by employing two quantum point contacts as spin injectors and detectors. Distinct engineering architectures of spin-orbit coupling are exploited for the quantum point contacts and the central semiconductor channel to achieve complete control of the electron spins -- spin injection, manipulation, and detection -- in a purely electrical manner. Such a device is compatible with large-scale integration and hold promise for future spintronic devices for information processing.
Funtionalized pentacene, 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene), field-effect transistors(FETs) were made by thermal evaporation or solution deposition method and the mobility was measured as a function of temperature and light power. The field-effect mobility ($mu$$_{rm FET}$) has a gate-voltage dependent activation energy. A non-monotonic temperature dependence was observed at high gate voltage (V$_G$ $<$ -30 V) with activation energy E$_a$ $sim$ 60 - 170 meV,depending on the fabrication procedure. The gate-voltage dependent mobility and non-monotonic temperature dependence indicates that shallow traps play important role in the transport of TIPS-pentacene films. The current in the saturation regime as well as mobility increase upon light illumination and is proportional to the light intensity, mainly due to the photoconductive response. Transistors with submicron channel length showed unsaturating current-voltage characteristics due to the short channel effect. Realization of simple circuits such as NOT(inverter), NOR, and NAND logic gates are demonstrated for thin film TIPS-pentacene transistors.
At the LaAlO$_3$-SrTiO$_3$ interface, electronic phase transitions can be triggered by modulation of the charge carrier density, making this system an excellent prospect for the realization of versatile electronic devices. Here, we report repeatable transistor operation in locally gated LaAlO$_3$-SrTiO$_3$ field-effect devices of which the LaAlO$_3$ dielectric is only four unit cells thin, the critical thickness for conduction at this interface. This extremely thin dielectric allows a very efficient charge modulation of ${sim}3.2times10^{13}$ cm$^{-2}$ within a gate-voltage window of $pm1$ V, as extracted from capacitance-voltage measurements. These also reveal a large stray capacitance between gate and source, presenting a complication for nanoscale device operation. Despite the small LaAlO$_3$ thickness, we observe a negligible gate leakage current, which we ascribe to the extension of the conducting states into the SrTiO$_3$ substrate.
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