Metal-semiconductor field-effect transistors (MESFETs) are widely known from opaque high-speed GaAs or high-power SiC and GaN technology. For the emerging field of transparent electronics, only metal-insulator-semiconductor field-effect transistors (MISFETs) were considered so far. This article reviews the progress of high-performance MESFETs in oxide electronics and reflects the recent advances of this technique towards transparent MESFET circuitry. We discuss design prospects as well as limitations regarding device performance, reliability and stability. The presented ZnO-based MESFETs and inverters have superior properties compared to MISFETs, i.e., high channel mobilities and on/off-ratios, high gain, and low uncertainty level at comparatively low operating voltages. This makes them a promising approach for future low-cost transparent electronics.

Transparent conductive oxides (TCOs) are a well-known material class allowing Ohmic conduction. A large free carrier concentration in the 10 21 cm À3 range and high conductivity (beyond 10 4 S/cm) is feasible simultaneously with high transparency. Applications are manifold and include touch screens and front contacts for displays or solar cells. Transparent semiconducting oxides (TSO) are oxides with an intermediate free carrier concentration (typically 10 14 -10 18 cm À3 ) allowing the formation of depletion layers. We review recent results on TSO-based transistors and inverters. Most work has been reported on MISFETs. We show that MESFETs exhibit high performance and low voltage operation of oxide electronics. MESFET-based inverters offer superior performance compared to results reported for TSO MISFET-based circuits.Optical image of inverter based on thin film MESFETs with Mg 0.003 Zn 0.997 O channels (left) and experimental inverter characteristic for supply voltage of V DD ¼ þ2:0 V (right).

The electrical properties of identically fabricated PtOx Schottky contacts on -oriented gallium oxide thin films and bulk crystals were investigated using current–voltage measurements at room temperature. The homogeneous barrier height of the Schottky contacts on thin films is 1.55 ± 0.15 eV, which is significantly smaller than that of those fabricated on bulk single crystals, 2.01 ± 0.12 eV. This large difference indicates an upward band bending of 0.4–0.5 eV at the surface of the bulk crystals in the as-received state, which is explained by the larger net doping density of the thin films compared to the single crystals.

Iridate thin films are a prerequisite for any application utilizing their cooperative effects resulting from the interplay of strong spin-orbit coupling and electronic correlations. Here, heteroepitaxial Na 2 IrO 3 thin films with (001) out-of-plane crystalline orientation and well-defined in-plane epitaxial relationship are presented on various oxide substrates. Resistivity is dominated by a three-dimensional variable-range hopping mechanism in a large temperature range between 300 K and 40 K. Optical experiments show the onset of a small optical gap E go ≈ 200 meV and a splitting of the Ir 5d-t 2g manifold. Positive magnetoresistance below 3 T and 25 K shows signatures of a weak antilocalization effect.Transition-metal oxides containing 5d iridium ions allow for the observation of novel cooperative effects resulting from an interplay between strong spin-orbit coupling and electronic correlations. These iridates are promising candidates for high-T C superconductors, 1 spin liquids, 2-4 a novel J eff = 1/2 Mottinsulating ground state, 5,6 and topological insulators. 7-10 A rather recently studied iridate is the Mott-insulating layered compound Na 2 IrO 3 where edge-sharing IrO 6 octahedra form a honeycomb lattice within each Na 2 IrO 3 layer. 11 Theoretical studies of magnetic interactions in model Hamiltonians of A 2 BO 3 -type compounds 12,13 suggest spin liquid behavior in Na 2 IrO 3 . On the other hand, tight-binding model analyses and first-principles band structure calculations, 7,10,14 as well as density-matrix renormalization group calculations, 15 suggest Na 2 IrO 3 as a possible topological insulator. Both states of matter, however, promise possible application in fault-tolerant quantum computation. [16][17][18] Experimental efforts on Na 2 IrO 3 were so far limited to powder and single-crystalline samples. 11,19-22 Initially, from x-ray diffraction experiments a monoclinic C2/c unit cell for Na 2 IrO 3 was suggested. 11 More recent experiments however are more consistent with a C2/m unit cell. 19,20 Later experiments also confirm the presence of trigonal distortions of the IrO 6 octahedra and that structural disorder, i.e., stacking faults and Na/Ir site mixings, is common. The compound furthermore exhibits frustrated antiferromagnetic order below T N = 15 K with moments ordered collinearly in a zigzag pattern. 19-21 Furthermore, single-crystalline Na 2 IrO 3 has a small band gap. 22 Its temperature-dependent in-plane dc electrical resistivity follows a ρ ∝ exp[(T 0 /T ) 1/4 ] behavior between 100 and 300 K. 11 Such a ρ(T ) dependence is usually associated with three-dimensional Mott variable range hopping 23 of localized carriers.In this paper, we report on heteroepitaxial Na 2 IrO 3 thin films grown on (001) YAlO 3 , a-sapphire, and c-sapphire. Deposition of Na 2 IrO 3 thin films ultimately is a step towards future device applications of this material. Our heteroepitaxial films exhibit a clear epitaxial relation and an excellent (001) out-of-plane orientation. In magnetoresistance measurements we obs...

We have investigated the electrical properties of metal-semiconductor field-effect transistors (MESFET) based on amorphous oxide semiconductor channels. All functional parts of the devices were sputter-deposited at room temperature. The influence on the electrical properties of a 150 °C annealing step of the gallium-indium-zinc-oxide channel is investigated. The MESFET technology offers a simple route for processing of the transistors with excellent electrical properties such as low subthreshold swing of 112 mV/decade, gate sweep voltages of 2.5 V, and channel mobilities up to 15 cm2/V s.