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Phototransistors made with two-dimensional transition metal dichalcogenides (TMDs) have shown excellent potential for nanoscale optoelectronic applications. In this work, we perform fully numerical...

Molybdenum disulfide (MoS2) field-effect transistor (FET)-based biosensors have attracted significant attention as promising candidates for highly sensitive, label-free biomolecule detection devices. In this paper, toward practical applications of biosensors, we demonstrate reliable and quantitative detection of a prostate cancer biomarker using the MoS2 FET biosensor in a nonaqueous environment by reducing nonspecific molecular binding events and realizing uniform chemisorption of anti-PSA onto the MoS2 surface. A systematic and statistical study on the capability of the proposed device is presented, and the biological binding events are directly confirmed and characterized through intensive structural and electrical analysis. Our proposed biosensor can reliably detect various PSA concentrations with a limit of 100 fg/mL. Moreover, rigorous theoretical simulations provide a comprehensive understanding of the operating mechanism of the MoS2 FET biosensors, and further suggests the enhancement of the sensitivity through engineering device design parameters.

Local-gate multilayer MoS2 phototransistors exhibit a photoresponsivity of up to 342.6 A W(-1) , which is higher by 3 orders of magnitude than that of global-gate multilayer MoS2 phototransistors. These simulations indicate that the gate underlap is critical for the enhancement of the photoresponsivity. These results suggest that high photoresponsivity can be achieved in indirect-bandgap multilayer MoS2 phototransistors by optimizing the optoelectronic design.

We present a low-cost 3D tracking system for virtual reality, gesture modeling, and robot manipulation applications which require fast and precise localization of headsets, data gloves, props, or controllers. Our system removes the need for cameras or projectors for sensing, and instead uses cheap LEDs and printed masks for illumination, and low-cost photosensitive markers. The illumination device transmits a spatiotemporal pattern as a series of binary Gray-code patterns. Multiple illumination devices can be combined to localize each marker in 3D at high speed (333Hz). Our method has strengths in accuracy, speed, cost, ambient performance, large working space (1m-5m) and robustness to noise compared with conventional techniques. We compare with a state-of-the-art instrumented glove and vision-based systems to demonstrate the accuracy, scalability, and robustness of our approach. We propose a fast and accurate method for hand gesture modeling using an inverse kinematics approach with the six photosensitive markers. We additionally propose a passive markers system and demonstrate various interaction scenarios as practical applications.

Thin-film transistors (TFTs) based on multilayer molybdenum diselenide (MoSe

We investigate bilayer phosphorene field-effect transistors (FETs) by self-consistent atomistic quantum transport simulations. Despite a penalty in electrostatic control for multiple layers, 10-nm-channel bilayer phosphorene FETs can exhibit excellent device characteristics, such as $\text{I}_{ {on}} >3$ mA/ $\mu \text{m}$ , large current ratio ( $> 10^{\mathrm { {7}}})$ , and small subthreshold swing (SS) of 66 mV/dec, with a double-gate device structure. While the scaling of gate dielectric monotonically enhances the overall performance of this device, channel length can only be scaled down to $\sim 8$ nm due to significant short-channel effects. We benchmark bilayer phosphorene FETs against bilayer MoS2 and WSe2 FETs along with a monolayer phosphorene device, which reveals that bilayer phosphorene FETs have favorable switching characteristics over other similar 2-D bilayer semiconductor devices, making both monolayer and bilayer phosphorene attractive for future switching applications. Our simulation results not only provide the performance and scaling limit of bilayer phosphorene FETs but also create irreplaceable insights into proper device design and parameter optimizations.

Thin-film transistors (TFTs) based on multilayer molybdenum diselenide (MoSe2 ) synthesized by modified atmospheric pressure chemical vapor deposition (APCVD) exhibit outstanding photoresponsivity (103.1 A W-1 ), while it is generally believed that optical response of multilayer transition metal dichalcogenides (TMDs) is significantly limited due to their indirect bandgap and inefficient photoexcitation process. Here, the fundamental origin of such a high photoresponsivity in the synthesized multilayer MoSe2 TFTs is sought. A unique structural characteristic of the APCVD-grown MoSe2 is observed, in which interstitial Mo atoms exist between basal planes, unlike usual 2H phase TMDs. Density functional theory calculations and photoinduced transfer characteristics reveal that such interstitial Mo atoms form photoreactive electronic states in the bandgap. Models indicate that huge photoamplification is attributed to trapped holes in subgap states, resulting in a significant photovoltaic effect. In this study, the fundamental origin of high responsivity with synthetic MoSe2 phototransistors is identified, suggesting a novel route to high-performance, multifunctional 2D material devices for future wearable sensor applications.

Hexagonal molybdenum diselenide (MoSe2) multilayers were grown by chemical vapor deposition (CVD). A relatively high pressure (>760 Torr) was used during the CVD growth to achieve multilayers by creating multiple nuclei based on the two-dimensional crystal growth model. Our CVD-grown multilayer MoSe2 thin-film transistors (TFTs) show p-type-dominant ambipolar behaviors, which are attributed to the formation of Se vacancies generated at the decomposition temperature (650 °C) after the CVD growth for 10 min. Our MoSe2 TFT with a reasonably high field-effect mobility (10 cm2/V · s) exhibits a high photoresponsivity (93.7 A/W) and a fast photoresponse time (τrise ~ 0.4 s) under the illumination of light, which demonstrates the practical feasibility of multilayer MoSe2 TFTs for photodetector applications.

By performing self-consistent quantum transport simulations using non-equilibrium Green's function (NEGF) formalism, monolayer molybdenum disulfide (MoS 2 ) field-effect transistors (FETs) with different types of contacts are investigated. We show that a MoS 2 transistor with doped reservoirs (MOSFET) is in general more favorable than a device with metal contacts (SBFET). In carefully designed switching conditions, a MoS 2 MOSFET has 67% higher ON current, 48% larger transconductance, 17% less output conductance, and subthreshold swing closer to 60 mV/dec, as compared to the SBFET counterpart. While both devices show significant loss in subthreshold swing and transconductance with extensive scaling (L ch < 6 nm), the MOSFET is more robust to short-channel effects.

We present a novel hand gesture interaction method which has a long-range working space 1m~5m overcoming conventional approaches' limitations in cost-performance dependency. Our camera-free interaction system is composed of a pair of lighting device and an instrumented glove with photosensor markers. The lighting devices spatiotemporally encode user's interaction space via binary infrared light signals and markers' 3D position at fingertips is tracked at high speed 250 Hz and fair accuracy 5mm at 3m working distance. Each marker consisting of a photosensor array allows a wide sensing range and minimizes fingers' self-occlusion. Experiment results demonstrate various applications where hand gestures are recognized as input commands to interact with digital information mimicking natural human hand gestures toward real objects. Our system has strengths in accuracy, speed, low price, and robustness comparing with conventional long-range interaction techniques. Ambiguity-free nature in marker recognition and little cost-performance dependency are additional advantages of our method.

2D layered transition metal dichalcogenides (TMDs), especially MoS2, has received great attention for next-generation semiconductor devices because their thin film transistors (TFTs) show a nearly ideal subthreshold swing (SS ≈ 70 mV decade-1), high on/off current ratio (I on/I off ≈ 108), and high field-effect mobility (µ eff > 100 cm2 V-1 s-1). In addition, TMDs have the optical characteristic of tuning bandgap from direct to indirect with increasing their layers. Even though photoresponsivity of multilayer MoS2 phototransistor due to its nature of indirect bandgap is lower than that of single layer MoS2, multilayer MoS2 has higher density-of-state and wider spectral response than single layer MoS2. In order to enhance photoresponsivity of multilayer MoS2 phototransistor, we suggest the phototransistor with local bottom gate structure (LBGS), where the bottom gate length of the device is shorter than the channel length. The underlap regions of between gate and channel work like the series resistance in dark state due to ineffective gate modulation at the region. To demonstrate the enhancement of phototransistor performance using LBGS, we previously studied amorphous silicon TFT with LBGS. The photosensitivity enhancement up to 64 times as compared to the conventional a-Si TFT. And then, we used multilayer MoS2 as a channel material to constitute phototransistor with LBGS. The giant photoreponsivity of 342.6 AW-1 at 2 mW cm-1 shows three orders of magnitude larger than that of global gate multilayer MoS2 TFTs. This result of our experiment and simulation reveals that multilayer MoS2 phototransistor with local bottom gate can be used as various photosensing devices.

Using self-consistent quantum transport simulations, we investigate the performance variability of monolayer molybdenum disulfide (MoS2) field-effect transistors (FETs) with various contact properties. Varying the Schottky barrier in MoS2 FETs affects the output characteristics more significantly than the transfer characteristics. If doped contacts are realized, the performance variation due to non-ideal contacts becomes negligible; otherwise, channel doping can effectively suppress the performance variability in metal-contact devices. Our scaling study also reveals that for sub-10-nm channels, doped-contact devices can be more robust in terms of switching, while metal-contact MoS2 FETs can undergo the smaller penalty in output conductance.