Abstract:We report on the direct measurement of two-dimensional sheet charge density dependence of electron transport in AlGaN/GaN high electron mobility transistors. Pulsed IV measurements established increasing electron velocities with decreasing sheet charge densities, resulting in saturation velocity of 1.9 x 10 7 cm/s at a low sheet charge density of 7.8 x 10 11 cm -2 . A new optical phonon emission-based electron velocity model for GaN is also presented. It accommodates stimulated LO phonon emission which clamps the electron velocity with strong electron-phonon interaction and long LO phonon lifetime in GaN. A comparison with the measured density-dependent saturation velocity shows that it captures the dependence rather well. Finally, the experimental result is applied in TCAD-based device simulator to predict DC and small signal characteristics of a reported GaN HEMT. Good agreement between the simulated and reported experimental results validated the measurement presented in this report and established accurate modeling of GaN HEMTs.a)
We demonstrate charge modulation of over 1014 cm−2 electrons in a two-dimensional electron gas formed in SrTiO3/GdTiO3 inverted heterostructure field-effect transistors. Increased charge modulation was achieved by reducing the effect of interfacial region capacitances through thick SrTiO3 cap layers. Transport and device characteristics of the heterostructure field-effect transistors were found to match a long channel field effect transistor model. SrTiO3 impurity doped metal–semiconductor field effect transistors were also demonstrated with excellent pinch-off and current density exceeding prior reports. The work reported here provides a path towards oxide-based electronics with extreme charge modulation exceeding 1014 cm−2.
Two-dimensional states in confined thin films of the three-dimensional Dirac semimetal Cd 3 As 2 are probed by transport and capacitance measurements under applied magnetic and electric fields. The results establish the two-dimensional Dirac electronic spectrum of these states. We observe signatures of p-type conduction in the two-dimensional states as the Fermi level is tuned across their charge neutrality point and the presence of a zero energy Landau level, all of which indicate topologically non-trivial states. The resistance at the charge neutrality point is approximately h/e 2 and increases rapidly under the application of a magnetic field. The results open many possibilities for gate-tunable topological devices and for the exploration of novel physics in the zero energy Landau level. 3
We report on the fabrication and electrical characteristics of the first SrTiO 3 /GdTiO 3 (STO/GTO) heterostructure field-effect transistors (HFETs). The high two-dimensional electron gas (2DEG) density of 3 Â 10 14 cm À2 formed due to the polar discontinuity at the STO/GTO interface was used as a channel to create inverted HFETs. Plasma O 2 treatment was found to reduce current leakage by 3 orders of magnitude at reverse bias, leading to rectifying Schottky behavior. A charge modulation of 0.6 Â 10 14 cm À2 is reported here, which represents the highest sheet charge modulated in any planar field effect transistor to date. V
Cadmium arsenide (Cd 3 As 2) 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 Cd 3 As 2 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 Cd 3 As 2 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.
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