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The structure of a gate-controlled graphene/germanium hybrid photodetector was optimized by splitting the active region to achieve highly sensitive infrared detection capability. The strengthened internal electric field in the split active junctions enabled efficient collection of photocarriers, resulting in a responsivity of 2.02 A W−1 and a specific detectivity of 5.28 × 1010 Jones with reduced dark current and improved external quantum efficiency; these results are more than doubled compared with the responsivity of 0.85 A W−1 and detectivity of 1.69 × 1010 Jones for a single active junction device. The responsivity of the optimized structure is 1.7, 2.7, and 39 times higher than that of previously reported graphene/Ge with Al2O3 interfacial layer, gate-controlled graphene/Ge, and simple graphene/Ge heterostructure photodetectors, respectively.

The intrinsic characteristics of novel devices and materials are often misunderstood due to the characterization methods which are developed to analyze existing devices or materials. Even though graphene is a very well-known material, there hasn't been a proper method to assess the density and energy levels of defects in graphene non-destructively, especially after the device fabrication. Here, we report a new non-destructive defect analysis method, amplitude-modulated discharge current analysis (AMDCA). The validity of this method was confirmed using a graphene field effect transistor with physically predefined defect densities in the channel. Charge trap densities ( N c t ) of the order of ∼1012 cm−2 were observed at the defect level in the range of 0.15–0.29 eV. This method can be very useful for the in-depth study of graphene devices as well as other two-dimensional materials that don't have a body contact.

Transistor-level annealing via the self-heating effect is useful for curing degraded gate dielectric in terms of quality and reliability. It has been speculated that the curing characteristics depend on the device state after post-metal annealing, but no conclusive evidence has been found so far. This work experimentally confirms the relationship between passivation gas species and curing characteristics during transistor-level annealing. It was confirmed that the existence of deuterium in a device was strongly associated with curing behavior.

Barrier height ( $\phi _{b}$ ), trap state, bandgap ( $E_{g}$ ), and band alignment information of the metal–ZrO2–metal capacitor have been extracted using internal photoemission (IPE) system. By correlating the IPE analysis with I-V and C-V characteristics obtained before and after rapid thermal annealing, origin and transformation of defect states have been successfully investigated. Our analysis revealed that deep-level defects originating from oxygen vacancies near the top electrode are causing of leakage current in MIM capacitor and these defects can be effectively reduced by a proper thermal annealing.

High-pressure (HP) deuterium (D2) annealing was applied to a gate-all-around (GAA) MOSFET to improve device reliability and memory performance. The structure had gate dielectrics of oxide–nitride–oxide (ONO), which completely straddled vertically stacked multiple silicon nanowires (Si-NWs) with n+ poly-Si gates. The HP D2 annealing was effective for the vertically stacked GAA MOSFET as it was for a conventional planar MOSFET. In addition, the resistance of the n+ poly-Si gate was also reduced after the HP D2 annealing. This is attributed to the passivation of defects among adjacent poly-Si grains by the HP D2. The reduced gate resistance ( ${R}_{G}$ ) is advantageous for decreasing RC delay. Direct characterizations of dc ${I}$ – ${V}$ and analyses of ac low-frequency noise (LFN) supported the abovementioned behaviors.

We investigate the development of gate-modulated tungsten diselenide (WSe2)-based lateral pn-homojunctions for visible and near-infrared photodetector applications via an effective oxygen (O2) plasma treatment. O2 plasma acts to induce the p-type WSe2 for the otherwise n-type WSe2 by forming a tungsten oxide (WOx) layer upon O2 plasma treatment. The WSe2 lateral pn-homojunctions displayed an enhanced photoresponse and resulted in open-circuit voltage (VOC) and short-circuit current (ISC) originating from the pn-junction formed after O2 plasma treatment. We further notice that the amplitude of the photocurrent can be modulated by different gate biases. The fabricated WSe2 pn-homojunctions exhibit greater photoresponse with photoresponsivities (ratio of the photocurrent and incident laser power) of 250 and 2000 mA/W, high external quantum efficiency values (%, total number of charge carriers generated for the number of incident photons on photodetectors) of 97 and 420%, and superior detectivity values (magnitude of detector sensitivity) of 7.7 × 109 and 7.2 × 1010 Jones upon illumination with visible (520 nm) and near-infrared lasers (852 nm), respectively, at low bias (Vg = 0 V and Vd = 1 V) at room temperature, demonstrating very high-performance in the IR region superior to the contending two-dimensional material-based photonic devices. These superior optoelectronic properties are attributed to the junctions induced by O2 plasma doping, which facilitate the effective carrier generation and separation of photocarriers with applied external drain bias upon strong light absorption.

Understanding the mechanism of thermal energy transport in a single nanotube (NT) is essential for successfully engineering nanostructured conducting polymers to apply to thermoelectrics or flexible electronic devices. We report the characterization of the in-plane thermal energy transport in a single poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) NT via direct measurement of the in-plane thermal conductivity (κ). We also demonstrate that the in-plane κ of PEDOT:PSS NT can be tuned within the range of 0.19 to 1.92 W·m-1·K-1 merely by changing the solvent used to treat the NTs in the post-fabrication stage. The in-plane thermal energy transport in a pristine NT, with its low in-plane κ, is primarily due to phonons; in a sulfuric acid-treated NT however, significant electronic contributions lead to a high in-plane κ. The present study will contribute to understanding the mechanism of thermal energy transport in highly disordered structures, such as conducting polymers, and to designing highly efficient polymer-based devices in which in-plane κ plays a pivotal role in determining the energy conversion efficiency.

A graphene photodetector decorated with Bi2Te3 nanowires (NWs) with a high gain of up to 3 × 104 and wide bandwidth window (400–2200 nm) has been demonstrated. The photoconductive gain was improved by two orders of magnitude compared to the gain of a photodetector using a graphene/Bi2Te3 nanoplate junction. Additionally, the position of photocurrent generation was investigated at the graphene/Bi2Te3 NWs junction. Eventually, with low bandgap Bi2Te3 NWs and a graphene junction, the photoresponsivity improved by 200% at 2200 nm (~0.09 mA/W).

We investigate the development of gate-modulated tungsten diselenide (WSe

This study demonstrates the utility of a printable ultrathin silicon dioxide (SiO2) substrate for developing highly transparent and flexible electronic devices. SiO2 provides a wider thermal process window than that of plastics, which is necessary for producing various electronics. To manipulate this fragile material, we employed a supportive handling substrate and transfer printing process using a sacrificial layer and protruding SU-8 anchors. In particular, we characterized the interfacial stress level and mechanics between the SiO2 substrate and the anchors during the retrieval process. We also manipulated the configuration of the corner of the SiO2 substrate to develop a reliable transfer printing process, which resulted in a high transfer yield with no distortion or fracture of the SiO2 patterns. As an example to demonstrate the utility of this method, we successfully developed a transparent and flexible thin-film inverter based on amorphous indium gallium zinc oxide (IGZO) with an 84.7% average optical transmittance on a polyethylene terephthalate (PET) film with an adhesive layer.

A tunable graphene doping method utilizing a SiO2/Si substrate with nanopores (NP) was introduced. Laser interference lithography (LIL) using a He–Cd laser (λ = 325 nm) was used to prepare pore size- and pitch-controllable NP SiO2/Si substrates. Then, bottom-contact graphene field effect transistors (G-FETs) were fabricated on the NP SiO2/Si substrate to measure the transfer curves. The graphene transferred onto the NP SiO2/Si substrate showed relatively n-doped behavior compared to the graphene transferred onto a flat SiO2/Si substrate, as evidenced by the blue-shift of the 2D peak position (∼2700 cm−1) in the Raman spectra due to contact doping. As the porosity increased within the substrate, the Dirac voltage shifted to a more positive or negative value, depending on the initial doping type (p- or n-type, respectively) of the contact doping. The Dirac voltage shifts with porosity were ascribed mainly to the compensation for the reduced capacitance owing to the SiO2–air hetero-structured dielectric layer within the periodically aligned nanopores capped by the suspended graphene (electrostatic doping). The hysteresis (Dirac voltage difference during the forward and backward scans) was reduced when utilizing an NP SiO2/Si substrate with smaller pores and/or a low porosity because fewer H2O or O2 molecules could be trapped inside the smaller pores.

The responsivity of a graphene photodetector was substantially enhanced by modulating the potential gradient in a chemical vapor deposition-grown graphene channel using asymmetric metal contacts such as Ti, Pd, and Au for the source and drain. The photoresponsivity of a graphene photodetector with an asymmetric Au–Ti contact combination increased to 52 mA/W at an illumination power density of 0.25 μW/cm2; this photoresponsivity is ∼63 times higher than that of a graphene photodetector having a symmetric Au–Au contact combination (0.82 mA/W).

A graphitic capping layer was successfully formed on top of Cu interconnects at room temperature, using a pulsed KrF laser. The change in temperature of the Cu line was maintained below 380 °C during laser irradiation with a fluence of 312.5 mJ/cm2. The resistance and critical current density of graphitic layer-capped Cu interconnects were improved by 2.8% and 5.2%, respectively. The lifetime of graphitic layer-capped Cu interconnects under a constant current stress was improved by 223%.

A large negative electrocaloric effect is demonstrated in an antiferroelectric ZrO2 thin film with 8 nm thickness deposited by atomic layer deposition. An adiabatic temperature change as high as ΔT = -31 K is obtained for an electric field change of ΔE = 3.45 MV cm-1 at an ambient temperature of 413 K. Moreover, the ZrO2 thin film shows enhanced stability as demonstrated by endurance and Preisach density maps. Due to its high phase transition temperature, high thermal stability, high scalability and full CMOS compatibility, ZrO2 is proposed as a promising candidate for future multilayer electrocaloric and solid-state cooling devices.

Chemical doping of transition metal dichalcogenides (TMDCs) has drawn significant interest because of its applicability to the modification of electrical and optical properties of TMDCs. This is of fundamental and technological importance for high-efficiency electronic and optoelectronic devices. Here, we present a simple and facile route to reversible and controllable modulation of the electrical and optical properties of WS2 and MoS2via hydrazine doping and sulfur annealing. Hydrazine treatment of WS2 improves the field-effect mobilities, on/off current ratios, and photoresponsivities of the devices. This is due to the surface charge transfer doping of WS2 and the sulfur vacancies formed by its reduction, which result in an n-type doping effect. The changes in the electrical and optical properties are fully recovered when the WS2 is annealed in an atmosphere of sulfur. This method for reversible modulation can be applied to other transition metal disulfides including MoS2, which may enable the fabrication of two-dimensional electronic and optoelectronic devices with tunable properties and improved performance.

Two-dimensional (2D) molybdenum disulfide (MoS2) atomic layers have a strong potential to be adopted for 2D electronic components due to extraordinary and novel properties not available in their bulk foams. Unique properties of the MoS2, including quasi-2D crystallinity, ultrahigh surface-to-volume, and a high absorption coefficient, have enabled high-performance sensor applications. However, implementation of only a single-functional sensor presents a limitation for various advanced multifunctional sensor applications within a single device. Here, we demonstrate the charge-transfer-based sensitive (detection of 120 ppb of NO2) and selective gas-sensing capability of the chemical vapor deposition synthesized MoS2 and good photosensing characteristics, including moderate photoresponsivity (∼71 mA/W), reliable photoresponse, and rapid photoswitching (500 ms). A bifunctional sensor within a single MoS2 device to detect photons and gas molecules in sequence is finally demonstrated, paving a way toward a versatile sensing platform for a futuristic multifunctional sensor.

A tunable graphene doping method utilizing a SiO

Graphene field effect transistors (GFETs) with top-gate and back-gate structures have been extensively used without much consideration for compatibility with graphene. A comparative study of the electrical characteristics of buried-gate GFETs and top-gate GFETs revealed that the performance of buried-gate GFETs is drastically enhanced by having a better gate controllability, achieving three times higher field effect mobility (~3000 cmlsupg2l/supg/Vs) than top-gate GFETs with on/off ratio ~10.Carrier scattering was also substantially improved by minimizing the fringing field effect, which is found to be the origin of high series resistance in top-gate GFETs. Moreover, we showed by electromagnetic (EM) simulation that the electric field distribution inside the transistors is more uniform at the buried-gate GFETs than the top-gate GFETs.

Various photodetectors showing extremely high photoresponsivity have been frequently reported, but many of these photodetectors could not avoid the simultaneous amplification of dark current. A gate-controlled graphene-silicon Schottky junction photodetector that exhibits a high on/off photoswitching ratio (≈104 ), a very high photoresponsivity (≈70 A W-1 ), and a low dark current in the order of µA cm-2 in a wide wavelength range (395-850 nm) is demonstrated. The photoresponsivity is ≈100 times higher than that of existing commercial photodetectors, and 7000 times higher than that of graphene-field-effect transistor-based photodetectors, while the dark current is similar to or lower than that of commercial photodetectors. This result can be explained by a unique gain mechanism originating from the difference in carrier transport characteristics of silicon and graphene.

A photodetector generating a nearly constant photocurrent in a very wide spectral range from ultraviolet (UV) to infrared has been demonstrated using chemical vapor deposited (CVD) graphene. Instability due to a photochemical reaction in the UV region has been minimized using an Al2O3 passivation layer, and a responsivity comparable to that of Highly Ordered Pyrolytic Graphite graphene photodetectors of ∼8 mA/W has been achieved at a 0.1 V bias, despite high defect density in the CVD graphene. A highly sensitive multi-band photodetector using graphene has many potential applications including optical interconnects, multi-band imaging sensors, highly sensitive motion detectors, etc.