Dongil Chu

Selective control of electron and hole tunneling in 2D assembly

A novel triode device controlled by a carrier type (namely, “carristor”) with ultrahigh on/off and rectification ratios is introduced. Recent discoveries in the field of two-dimensional (2D) materials have led to the demonstration of exotic devices. Although they have new potential applications in electronics, thermally activated transport over a metal/semiconductor barrier sets physical subthermionic limitations. The challenge of realizing an innovative transistor geometry that exploits this concern remains. A new class of 2D assembly (namely, “carristor”) with a configuration similar to the metal-insulator-semiconductor structure is introduced in this work. Superior functionalities, such as a current rectification ratio of up to 400,000 and a switching ratio of higher than 106 at room temperature, are realized by quantum-mechanical tunneling of majority and minority carriers across the barrier. These carristors have a potential application as the fundamental building block of low–power consumption electronics.

Room temperature ferromagnetic and ambipolar behaviors of MoS2 doped by manganese oxide using an electrochemical method

We report the room temperature ferromagnetic and ambipolar behaviours of MoS2 thin flakes doped with MnO2 by electrochemical adsorption. The MoS2 thin film was determined to be multilayered over four layers from Raman analysis. The Mn-oxide doped MoS2 has a ferromagnetic hysteresis at room temperature and showed a weak remnant magnetization, 0.02 emu/g. From the gate dependent transfer characteristics of the MoS2 field effect transistor, it appeared that the Mn-oxide doped MoS2 has ambipolar behaviours with field effect mobilities of about 3.7 and 16.3 cm2 V−1 s−1, respectively, for electrons and holes.

Semiconducting properties of perchlorate-doped graphene using an electrochemical method

We report a band gap opening and p-type doping for single layer graphene by an electrochemical method. The chlorine oxide doping to graphene was carried out in 0.1 M LiClO4/acetonitrile solution. The temperature dependent conductivity of the p-type doped graphene at an applied potential of 1.5 V during the electrochemical doping process showed the band gap of 0.094 eV.

Locally Gated SnS 2 /hBN Thin Film Transistors with a Broadband Photoresponse

Next-generation flexible and transparent electronics demand newer materials with superior characteristics. Tin dichalcogenides, Sn(S,Se)2, are layered crystal materials that show promise for implementation in flexible electronics and optoelectronics. They have band gap energies that are dependent on their atomic layer number and selenium content. A variety of studies has focused in particular on tin disulfide (SnS2) channel transistors with conventional silicon substrates. However, the effort of interchanging the gate dielectric by utilizing high-quality hexagonal boron nitride (hBN) still remains. In this work, the hBN coupled SnS2 thin film transistors are demonstrated with bottom-gated device configuration. The electrical transport characteristics of the SnS2 channel transistor present a high current on/off ratio, reaching as high as 105 and a ten-fold enhancement in subthreshold swing compared to a high-κ dielectric covered device. We also demonstrate the spectral photoresponsivity from ultraviolet to infrared in a multi-layered SnS2 phototransistor. The device architecture is suitable to promote diverse studied on flexible and transparent thin film transistors for further applications.

Enhancement of near-infrared detectability from InGaZnO thin film transistor with MoS2 light absorbing layer

We report an enhancement of near-infrared (NIR) detectability from amorphous InGaZnO (α-IGZO) thin film transistor in conjunction with randomly distributed molybdenum disulfide (MoS2) flakes. The electrical characteristics of the α-IGZO grown by radio-frequency magnetron sputtering exhibit high effective mobility exceeding 15 cm2 V-1 s-1 and current on/off ratio up to 107. By taking advantages of the high quality α-IGZO and MoS2 light absorbing layer, photodetection spectra are able to extend from ultra-violet to NIR range. The α-IGZO channel detector capped by MoS2 show a photo-responsivity of approximately 14.9 mA W-1 at 1100 nm wavelength, which is five times higher than of the α-IGZO device without MoS2 layer.

High photoresponsivity from multilayer MoS2/Si heterojunction diodes formed by vertically stacking

We investigated a vertically stacked p+-n heterojunction diode consisting of a two-dimensional (2D) molybdenum disulfide (MoS2) crystal and a heavily doped p+-type Si substrate. The MoS2 flakes are transferred onto p+-Si substrates by using a scotch tape-based exfoliation method. The performances of n-MoS2/p+-Si diodes are investigated by I-V measurement under light illumination using light emitting diodes with various wavelengths. It appears that multilayer MoS2 has sufficient thickness to absorb incident light from the visible to near-infrared range with a high sensitivity. With the advantages of a simple device structure as well as improved contact quality between the MoS2 and silicon interface, an ideality factor of 1.09 can be achieved. The diodes reveal an ultra-high photoresponsivity of about 980 A/W at a wavelength of 525 nm with a strong dependence on the light wavelength and intensity, while they show a high specific detectivity on the order of 109 cm·Hz1/2/W from the visible to near infrared sp...