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With the advent of the trillion sensor era, molybdenum disulfide (MoS2) offers intriguing future optical device opportunities due to qualities such as its novel optoelectronic properties and preferable form factors. However, while a fundamental understanding of device reliability under illumination is significantly important, most of the previous research has focused on persistent photocurrent (PPC) effects. For this reason, understanding of a clear mechanism remains elusive. Herein the work reported, electrical‐bias‐dependent device instability and net optical illumination effects of MoS2 thin‐film transistors (TFTs) are experimentally evaluated to decouple the origins of device instability coming from either net electrical bias stress or illumination stress. In addition, time‐dependent monitoring of relaxation behaviors under illumination at different wavelength hints that excess carrier generation and remnant electrons after annihilation during illumination play a key role in determination of photo‐initiated instability of a device. For practical suppression of device instability under ambient light, an operation scheme (using trapping time increase under positive bias) is adroitly utilized to provide reliable device performance. Systematic understanding of device instability of MoS2 TFTs, and of their suppression principles, is potentially beneficial for the design of next‐generation devices on the basis of 2D materials. [ABSTRACT FROM AUTHOR]

The development of transition metal dichalcogenides (TMDCs) and quantum dots (QDs) as the promising semiconductor and emitter is carried out in diverse applications. Despite superb research progress, study of emerging devices incorporated with TMDC thin film transistors (TFTs) and quantum dot light‐emitting diodes (QLEDs) is rarely reported. Herein, the QLEDs operation controlled by p (or n‐type) molybdenum ditelluride (MoTe2) TFTs with the realization of complementary type transistor is first demonstrated. In this study, molecular doping by poly‐L‐lysine (PLL) is adopted for a type conversion of MoTe2 TFTs and surface ligand modification is utilized for improvement of QLED performance. As a result, the PLL treatment achieves the outstanding type conversion of MoTe2 TFTs without any degradation of electrical properties, leading to securing reliable n or p‐type devices, thus, availability of complementary circuits. Furthermore, ligand modified QDs capped with octylamine result in balanced electron/hole injection in QLEDs, yielding improved current efficiency (ηA = 13.9 cd A−1) and longer lifetimes (T50 = 66 h at L0 = 3000 cd m−2). Lastly, MoTe2 TFTs demonstrate their capabilities to drive the QLEDs for the envisioned application including display backplane transistor with decent switching properties, immunity for generation of photocurrent, and operation stability. [ABSTRACT FROM AUTHOR]

Confronted by the inherent physical limitations in scaling down Si technology, transition metal dichalcogenides (TMDCs) as alternatives are being tremendously researched and paid attention to. However, mature counter doping technology for TMDCs is still elusive, and thus, a controllable and reversible charge enhancer is adopted for acceptor (or donor)-like doping via octadecyltrichlorosilane (ODTS) (or poly-L-lysine (PLL)) treatment. Furthermore, multiple counter doping for TMDC field-effect transistors (FETs), combined with a threshold voltage (Vth) freezing scheme, renders the Vth modulation controllable, with negligible degradation and decent sustainability of FETs even after each treatment of a representative charge enhancer. In parallel, the counter doping mechanism is systematically investigated via photoluminescence spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy (AFM), surface energy characterization, and measurement of optoelectronic properties under illumination with light of various wavelengths. More impressively, complementary inverters, composed of type-converted molybdenum ditelluride (MoTe2) FETs and hetero-TMDC FETs in enhancement mode, are demonstrated via respective ODTS/PLL treatments. Herein, driving backplane application for micro-light-emitting diode (µ-LED) displays and physical validation of a corresponding counter doping scheme even for flexible polyethylene terephthalate (PET) substrates could be leveraged to relieve daunting challenges in the application of nanoscale Si-based three-dimensional (3D) stacked systems, with potential adoption of ultralow power and monolithic optical interconnection technology. [ABSTRACT FROM AUTHOR]

For robustness on security and ultralow power consumption for Internet of Things (IoT) sensors, including ultraminiaturization for high chip density, 2D multilayered ReS2 field‐effect transistors (FETs) combined with photoinsensitive single‐walled carbon nanotube (SWNT) FETs are demonstrated for application in light‐to‐frequency (LTF) conversion circuits. Herein, multilayered ReS2 FETs with a direct bandgap (≈1.5 eV) have discernible photoresponsivity of ≈17 A W−1 for red and ≈128 A W−1 for green, respectively, with photodetectivity (≈109 Jones), leading to excellent operation for photosensitive inverters, partly associated with the photoinsensitive SWNT FETs for p‐channel devices. Moreover, the electrical parameters for photosensitive complementary inverters, according to different wavelengths in the dark and under, red (λR = 660 nm), green (λG = 530 nm), and blue (λB = 450 nm) light, are experimentally extracted, and their SPICE simulation‐based validation on working principles of ring oscillators (ROs) is confirmed under light illumination. More impressively, ultralow power consumption for the proposed scheme is achieved due to both the direct bandgap and the large‐energy bandgap, as compared with conventional multilayered MoS2 FET‐based photosensitive inverters, rationally validating the promising opportunity for applications in the envisioned IoT sensor systems. [ABSTRACT FROM AUTHOR]

Herein, as one of bias‐dependent channel leakage issues in p‐channel multilayered molybdenum ditelluride field‐effect transistors (m‐MoTe2 FETs), anomalous increase in off‐state current is reproducibly observed with increase in drain‐to‐gate voltage (VDG), even after hydrophobic, cyclic transparent optical polymer (CYTOP) encapsulation. For elucidation on the behind mechanism for the phenomena, drain‐ and gate‐bias dependent channel leakage currents are systematically analyzed in the range of temperature 100 to 380 K. Surprisingly, analysis on trap‐assisted indirect tunneling current substantiates that the off‐state current is mainly attributed to gate‐induced drain leakage (GIDL) current associated with band bending in m‐MoTe2 FETs. Moreover, linear slope (0.00163) of ln (IDS/F) versus F1/2 plot and its coincidence with theoretical value (0.00148) identify that thermal emission associated with Poole–Frenkel effect is strongly involved at low drain bias of −1.1 V (e.g., effective barrier height, ϕB ≈ 0.61 eV), whereas GIDL current becomes more predominant at high drain bias of −3.1 V (ϕB ≈ 0.51 eV). Thus, in‐depth understanding on the origin of anomalous leakage current and its systematic validation would be beneficial for the development of novel devices and circuits based on transition metal chalcogenides (TMDCs). [ABSTRACT FROM AUTHOR]

In this article, the bias stress instability (BSI) of multilayered MoS2 field-effect transistors (m-MoS2 FETs) encapsulated in hydrophobic polymers [cyclized transparent optical polymer (CYTOP)] was systematically investigated under the pulse-mode operation. Compared with the dc mode, the threshold voltage shift (Δ Vth) under positive-bias stress was inversely larger than that for negative-bias stress. BSI in the m-MoS2 FETs with CYTOP was negligibly affected by the external oxygen/moisture. Shallow hole traps and electron detrapping effects were strongly identified as the main causes of bias-polarity dependence on Δ Vth in the pulse mode. This can potentially be attributed to the sulfur vacancies in the m-MoS2, which have a short trap lifetime of hundreds of microseconds. During the pulse-mode operation, various parameters, such as duty cycle, timeframe, bias polarity, and electric field strength, were systematically adjusted and experimentally applied to elucidate the origins of the asymmetry of the BSI in pulse mode. Atomic- and energy-band models, as well as recovery time constant extraction, are suggested to support the key mechanism of bias-polarity effects on BSI, which are, nicely, consistent with previous reports. [ABSTRACT FROM AUTHOR]

Here, bias stress instability on multilayered MoTe2 field effect transistors (m‐MoTe2 FETs) with encapsulation of hydrophobic polymers (cyclic transparent optical polymer) is systematically investigated under DC and pulse mode operation. During DC mode stress, the threshold voltage shift (ΔVth) under positive bias stress is at least three times larger than that of negative stress due to high hole barrier (∼0.57 eV), compared with electron barrier (∼0.18 eV). However, ΔVth in positive pulse mode stress is significantly reduced with decrease of a duty cycle, as compared with that of negative stress. With isolation from external gas ambient effects such as H2O and O2, shallow electron traps in multilayered MoTe2 field effect transistors are identified as one of strong candidates to cause bias polarity dependency on ΔVth in pulse mode. Moreover, recovery time for traps, involved during positive bias stress, is six times faster than that of negative stress, substantiating that shallow electron traps and their fast detrapping are one of key origins. In practice, optimisation of pulse mode operation via bipolar switching can be potentially utilised for minimisation of device instability during the operation of multilayered MoTe2 field effect transistors devices and their circuits. [ABSTRACT FROM AUTHOR]

Herein, GaN driver FETs with a high-energy bandgap are employed in photosensitive inverters to eliminate light-shield layers (LSLs). This configuration exhibits the full-swing characteristics of photosensitive inverters comprised of multi-layered MoS2 FET loads in the photosensitive pseudo-depletion mode. The GaN FETs provide both high current drivability and excellent photo-leakage immunity under visible light. This allows the photosensitive inverters to be successfully operational without LSLs. The relative degradation (%) of voltage gain for photosensitive inverters with GaN drivers from dark to blue light exposure is improved from 67.7% to 53.0%, as compared to previously reported MoS2 inverters with LSLs. [ABSTRACT FROM AUTHOR]