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Amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) have attracted much attention owing to their promising applications, such as display devices and dynamic random access memory (DRAM) devices. This study reports a comprehensive study on the bias temperature instability of a-IGZO TFTs. We analyzed the behavior of transfer characteristics, under repeated bias stress and recovery at different temperatures, to unveil the degradation mechanism of bias and thermal stress. Based on threshold voltage, subthreshold swing, and field-effect mobility, the correlation between transfer characteristics and stress time was found to depend on temperature, revealing the opposite trends. The trends are interpreted using two mechanisms: trapped electron and oxygen vacancy. The consequential behavior of transfer characteristics under repeated stress and recovery depended on the competition between the two mechanisms, and the result of the competition depended on the temperature. The predominant mechanism was determined based on the temperature, and a high temperature enhanced the generation of oxygen vacancies, resulting in a negative shift at high temperatures. Repeated stress revealed that the predominant mechanisms were maintained with constant VT shifts over cycles, and repeated recovery confirmed the difference in recovery mechanisms with increasing VT shifts over cycles. Understanding the competition between the two main mechanisms aids in explaining the bias temperature instability of a-IGZO TFTs. [ABSTRACT FROM AUTHOR]

Stacking of atomically thin layers of two-dimensional materials has revealed extraordinary physical phenomena owing to van der Waals (vdW) interaction at the interface. However, most of the studies focused on the transition metal dichalcogenide (TMD)/TMD heterostructure, while the interlayer coupling of the TMD/hexagonal boron nitride (h-BN) heterostructure has not been extensively explored despite its importance. In this study, the temperature-dependent interlayer coupling is demonstrated in a heterostructure of molybdenum disulfide (MoS2) and h-BN. The interface between MoS2 and the insulating substrate exerts a significant spectroscopic impact on MoS2 through substrate-induced local strain, charged impurity, and vdW interactions. Under non-resonant conditions, temperature-dependent peak shifts in Raman and photoluminescence (PL) spectra of MoS2 reveal the evolution of interlayer coupling. Phonon frequencies and PL peak energies at different temperatures demonstrate how substrate-induced strain, impurity, and vdW interactions at the interface influence phonon vibration and excitonic transition of MoS2. Under resonant conditions at low temperature, anomalous Raman modes appear in the MoS2/h-BN heterostructure because of the enhanced electron-phonon coupling and vdW interactions. The anomalous Raman modes are quantitatively investigated by the deconvolution of the resonance Raman spectra and described by interlayer coupling at low temperature, in agreement with complementary indications from the temperature-dependent evolution of non-resonant Raman and PL spectra. [ABSTRACT FROM AUTHOR]

Plasmonic coupling provides a highly localized electromagnetic field in the gap of noble metals when illuminated by a light. The plasmonic field enhancement is generally known to be inversely proportional to the gap distance. Given such a relation, reducing the gap distance appears to be necessary to achieve the highest possible field enhancement. At the sub-nanometer scale, however, quantum mechanical effects have to be considered in relation to plasmonic coupling. Here, we use graphene as a spacer to observe plasmonic field enhancement in sub-nanometer gap. The gap distance is precisely controlled by the number of stacked graphene layers. We propose that the sudden drop of field enhancement for the single layer spacer is originated from the plasmon tunneling through the thin spacer. Numerical simulation which incorporates quantum tunneling is also performed to support the experimental results. From the fact that field enhancement with respect to the number of graphene layers exhibits different behavior in two wavelengths corresponding to on- and off-resonance conditions, tunneling phenomenon is thought to destroy the resonance conditions of plasmonic coupling. [ABSTRACT FROM AUTHOR]

Hexagonal boron nitride (h-BN) has been previously manufactured using mechanical exfoliation and chemical vapor deposition methods, which make the large-scale synthesis of uniform h-BN very challenging. In this study, we produced highly uniform and scalable h-BN films by plasma-enhanced atomic layer deposition, which were characterized by various techniques including atomic force microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray diffraction. The film composition studied by X-ray photoelectron spectroscopy and Auger electron spectroscopy corresponded to a B:N stoichiometric ratio close to 1:1, and the band-gap value (5.65 eV) obtained by electron energy loss spectroscopy was consistent with the dielectric properties. The h-BN-containing capacitors were characterized by highly uniform properties, a reasonable dielectric constant (3), and low leakage current density, while graphene on h-BN substrates exhibited enhanced electrical performance such as the high carrier mobility and neutral Dirac voltage, which resulted from the low density of charged impurities on the h-BN surface. [ABSTRACT FROM AUTHOR]