Publications by authors named "Yaoqiao Hu"

This study provides a comprehensive structural, chemical, and optical characterization of CZTS thin films deposited on flexible Kapton substrates via the Successive Ionic Layer Adsorption and Reaction (SILAR) method. The investigation explored the effects of varying deposition cycles (40, 60, 70, and 80) and annealing treatments on the films. An X-ray diffraction (XRD) analysis demonstrated enhanced crystallinity and phase purity, particularly in films deposited with 70 cycles.

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Manipulating the crystal orientation plays a crucial role in the conversion efficiency during second harmonic generation (SHG). Here, we provide a new strategy in controlling the surface-dependent anisotropic SHG with the precise design of (101) and (2 0) MAGeI facets. Based on the SHG measurement, the (101) MAGeI single crystal exhibits larger SHG (1.

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The high contact resistance of transition metal dichalcogenide (TMD)-based devices is receiving considerable attention due to its limitation on electronic performance. The mechanism of Fermi level () pinning, which causes the high contact resistance, is not thoroughly understood to date. In this study, the metal (Ni and Ag)/Mo-TMD surfaces and interfaces are characterized by X-ray photoelectron spectroscopy, atomic force microscopy, scanning tunneling microscopy and spectroscopy, and density functional theory systematically.

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Ion diffusion is a fundamentally important process in understanding and manipulating the optoelectronic properties of semiconductors. Most current studies on ionic diffusion have been focusing on perovskite polycrystalline thin films and nanocrystals. However, the random orientation and grain boundaries can heavily interfere with the kinetics of ion diffusion, where the experimental results only reveal the average ion exchange kinetics and the actual ion diffusion mechanisms perpendicular to the direction of individual crystal facets remain unclear.

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Tungsten transition metal dichalcogenides (W-TMDs) are intriguing due to their properties and potential for application in next-generation electronic devices. However, strong Fermi level (E) pinning manifests at the metal/W-TMD interfaces, which could tremendously restrain the carrier injection into the channel. In this work, we illustrate the origins of E pinning for Ni and Ag contacts on W-TMDs by considering interface chemistry, band alignment, impurities, and imperfections of W-TMDs, contact metal adsorption mechanism, and the resultant electronic structure.

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Article Synopsis
  • - Two-dimensional (2D) materials and their heterostructures are seen as key players for future electronics, but face challenges in growth precision, domain consistency, and scalability for commercial use.
  • - A new confined-growth technique addresses these issues by allowing for controlled layer-by-layer growth of single-domain 2D monolayer arrays on various substrates using patterned SiO masks.
  • - This method enables the creation of high-quality wafer-scale arrays of materials like WSe and heterostructures like MoS/WSe, paving the way for 2D materials to be integrated into industrial applications.
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In this work, an AlGaN-based Deep-Ultraviolet Light-Emitting Diode structure has been designed and simulated for the zincblende and wurtzite approaches, where the polarization effect is included. DFT analysis was performed to determine the band gap direct-to-indirect cross-point limit, AlN carrier mobility, and activation energies for p-type dopants. The multiple quantum wells analysis describes the emission in the deep-ultraviolet range without exceeding the direct-to-indirect bandgap cross-point limit of around 77% of Al content.

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Solid state quantum defects are promising candidates for scalable quantum information systems which can be seamlessly integrated with the conventional semiconductor electronic devices within the 3D monolithically integrated hybrid classical-quantum devices. Diamond nitrogen-vacancy (NV) center defects are the representative examples, but the controlled positioning of an NV center within bulk diamond is an outstanding challenge. Furthermore, quantum defect properties may not be easily tuned for bulk crystalline quantum defects.

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High drive current is a critical performance parameter in semiconductor devices for high-speed, low-power logic applications or high-efficiency, high-power, high-speed radio frequency (RF) analogue applications. In this work, we demonstrate an InO transistor grown by atomic layer deposition (ALD) at back-end-of-line (BEOL) compatible temperatures with a record high drain current in planar FET, exceeding 10 A/mm, the performance of which is 2-3 times better than all known transistors with semiconductor channels. A high transconductance reaches 4 S/mm, recorded among all transistors with a planar structure.

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Yellow-green luminescence (YGL) competes with near-bandgap emission (NBE) for carrier recombination channels, thereby reducing device efficiency; yet uncovering the origin of YGL remains a major challenge. In this paper, nearly stress-free and low dislocation density self-assembled GaN microdisks were synthesized by Na-flux method. The YGL of GaN microdisks highly depend on their polar facets.

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The development of high-performance p-type oxides with wide band gap and high hole mobility is critical for the application of oxide semiconductors in back-end-of-line (BEOL) complementary metal-oxide-semiconductor (CMOS) devices. SnO has been intensively studied as a high-mobility p-type oxide due to its low effective hole mass resulting from the hybridized O-2p/Sn-5s orbital character at the valence band edge. However, SnO has a very small band gap (∼0.

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Exploiting two-dimensional (2D) materials with natural band gaps and anisotropic quasi-one-dimensional (quasi-1D) carrier transport character is essential in high-performance nanoscale transistors and photodetectors. Herein, the stabilities, electronic structures and carrier mobilities of 2D monolayer ternary metal iodides MLaI(M = Mg, Ca, Sr, Ba) have been explored by utilizing first-principles calculations combined with numerical calculations. It is found that exfoliating MLaImonolayers are feasible owing to low cleavage energy of 0.

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In this work, we demonstrate enhancement-mode field-effect transistors by an atomic-layer-deposited (ALD) amorphous InO channel with thickness down to 0.7 nm. Thickness is found to be critical on the materials and electron transport of InO.

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We have studied the Mg doping of cubic GaN grown by plasma-assisted Molecular Beam Epitaxy (PA-MBE) over GaAs (001) substrates. In particular, we concentrated on conditions to obtain heavy p-type doping to achieve low resistance films which can be used in bipolar devices. We simulated the Mg-doped GaN transport properties by density functional theory (DFT) to compare with the experimental data.

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Indium (In) out-diffusion through high-k oxides severely undermines the thermal reliability of the next generation device of III-V/high-k based metal oxide semiconductor (MOS). To date, the microscopic mechanism of In diffusion is not yet fully understood. Here, we utilize angle resolved X-ray photoelectron spectroscopy (ARXPS) and density functional theory (DFT) to explore In diffusion in high-k oxide HfO2.

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