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High-performance antifog coatings are critical for devices operating in high-humidity environments, such as endoscopes. However, existing antifog coatings have been unable to achieve good antifoggi...

Multiple-stimuli-responsive photoluminescence films based on a ZnII -organic framework, {[Zn2 (Htpim)(3,4-pydc)2 ]⋅4 DMF⋅4 H2 O}n (1, Htpim=2,4,5-tri(4-pyridyl)imidazole, 3,4-H2 pydc=3,4-pyridinedicarboxylic acid), were fabricated. This compound consisted of a 2D corrugated layer, {Zn(3,4-pydc)}n , which was further pillared using a Y-shaped pillar N-donor ligand (Htpim) to form a 3D-pillared-layer framework with 1D open channels. The rectangular channels in the as-synthesized compound are fully occupied by guest DMF and H2 O molecules. The framework exhibits instant and reversible thermochromic properties corresponding to the removal of different H2 O and DMF guest molecules as temperature increases. The pale-yellow crystal undergoes significant redshifting to a greenish emission centered at 530 nm. Compound 1 also showed remarkable solvatochromic effects in the presence of various organic solvents without affecting its structural integrity. In addition, polycrystalline MOF films were grown on an α-Al2 O3 support for switchable and fast-response thermochromic and solvatochromic sensors.

Comparing the aperture size of a membrane to the kinetic diameters of gases to be separated has long been regarded as the rule of thumb for identifying potential membrane materials. This method based upon molecular sieving could however fail for CO2 separations using metal-organic frameworks (MOFs). While the challenge may be attributed to the breathing effect or linker rotation for some highly flexible MOFs, the adsorbent-adsorbate Coulombic interaction can also significantly influence the diffusion of CO2 in MOFs. This work is aimed to investigate how the Coulombic interaction can alter the free energy profile of CO2 in a MOF channel. MOFs with one-dimensional (1D) channels (98 structures) in the orthorhombic system are probed in this in silico study. Coulombic interactions are identified to cause a notable offset between the transport bottleneck (the spot where the free energy reaches maximum) and the topological bottleneck (the spot where the pore limiting diameter is located). As a result, the transport bottleneck of CO2 and that of H2 or CH4 are found to be at different locations for a decent portion of studied MOF structures. This makes the pore limiting diameter of a MOF fail to serve as an effective indicator for molecular sieving. This study also investigates the Coulombic effect on the permeability of CO2 in MOFs, and suggests that a highly CO2 permeable and selective MOF would have strong CO2 adsorption sites that create an energetically homogeneous channel for transport. Finally, we also discuss the Coulombic effect on the diffusion of CO2 in MOFs when their flexibility is considered.

We present a fully integrated 7nm CMOS platform featuring a 3rd generation finFET architecture, SAQP for fin formation, and SADP for BEOL metallization. This technology reflects an improvement of 2.8X routed logic density and >40% performance over the 14nm reference technology described in [1-3]. A full range of Vts is enabled on-chip through a unique multi-workfunction process. This enables both excellent low voltage SRAM response and highly scaled memory area simultaneously. The HD 6-T bitcell size is 0.0269um2. This 7nm technology is fully enabled by immersion lithography and advanced optical patterning techniques (like SAQP and SADP). However, the technology platform is also designed to leverage EUV insertion for specific multi-patterned (MP) levels for cycle time benefit and manufacturing efficiency. A complete set of foundation and complex IP is available in this advanced CMOS platform to enable both High Performance Compute (HPC) and mobile applications.

We investigate Al2O3/AlGaN interface in GaN MOSHEMTs to engineer channel mobility and threshold voltage suitable for power switching applications. Using oxygen-plasma and annealing treatments, we find the optimal window for high mobility and threshold voltage. Next, we discuss the power switching figure of merit of high composition AlGaN based HEMTs and their potential to achieve large threshold voltages. Finally, we characterize the electrical properties of the interface between Al2O3/high composition Al0.7Ga0.3N, and measure the conduction band offset of approximately 1 eV with a low positive interface fixed charge density of +2.5 × 1012 cm−2.

We demonstrate an efficient approach to engineer the dielectric/AlGaN positive interface fixed charges by oxygen plasma and post-metallization anneal. Significant suppression of interface fixed charges from 2 × 1013 to 8 × 1012 cm-2 was observed. Experimental and theoretical electron mobility characteristics and the impact of remote impurity scattering were investigated. The reduction in oxide/semiconductor interface charge density leads to an increase of electron mobility, and enables a positive threshold voltage.

We have performed first-principles calculations to investigate the origin of adsorption of platinum on nitrogen- and boron-doped carbon nanotubes (CNTs). Our calculation results reveal that both nitrogen- and boron-doped CNTs can assist the reactivity of platinum adsorption on the CNT surface, although the detailed mechanisms are very different. For nitrogen-doped CNTs, the enhanced adsorption results from activation of the nitrogen-neighboring carbon atoms due to the large electron affinity of nitrogen. In this case, the nitrogen atoms mediate the platinum adsorption enhancement on the CNT surface. In contrast, the enhanced platinum adsorption in boron-doped CNTs can be attributed to the strong hybridization between the platinum d orbital and boron p orbital. Our results explain the experimentally observed enhanced adsorption of platinum on nitrogen-doped CNTs and also suggest that boron-doped CNTs may be a better candidate for fuel cell applications.

In this work, we have used electrostatic engineering of the ALD dielectric/III-nitride interface to do lateral band engineering in a III-nitride HEMT. Due to challenges related to dopant activation and damage anneal, traditional ion implantation and diffusion techniques for lateral band engineering that are commonly used in other semiconductors, cannot be applied easily in the III-nitride system. We have developed an alternate method that uses surface fixed charges to engineer lateral energy band profiles, and used this to demonstrate an enhancement-mode AlGaN/GaN HEMT without any gate recess. Metal-insulator-semiconductor high electron mobility transistors (MISHEMTs) based on the III-Nitride system can efficiently suppress gate leakage enabling lower gate-channel spacing for high frequency transistors, and low off-state leakage for power switching devices. Conventional normally-off MISHEMTs require precise etching control for recess gate [1] or heavy p+ doping for the junction gate [2]. However, plasma etching may induce variation of electrical characteristics caused by surface damage while p-doping can cause hysteresis. In this work, we show a new technique to achieve normally off AlGaN/GaN transistors. Our method exploits the interface properties of dielectric/III-nitride, where a high density of fixed charges of the order of 1 μC/cm 2 can be formed the interface of atomic layer deposited (ALD) dielectrics on GaN and AlN[3-5]. In this work, we use the combination of oxygen plasma and post metallization anneal (PMA) treatments to engineer the Al 2 O 3 /AlGaN (AlN) interface fixed charges. Based on this technology, lateral energy band engineering by patterning ALD Al 2 O 3 is demonstrated. This technology provides a new approach to recess-free and doping-free normally-off MOSFETs /MISHEMTs.

Atomic layer deposited Al2O3/III-nitride interfacial charge properties were investigated experimentally. Substantial amount of positive interface fixed charges (> 1.8×1013 cm-2) were observed on all the orientations of GaN and Ga-polar AlGaN. These interface charges bring large impact on electron transport especially in vertically scaled devices. Post-metallization anneals is one of the methods which can significantly alter this sheet charge in the case of Al2O3 on GaN. Oxygen plasma is another approach to efficiently reduce the interface charges at Al2O3/AlGaN. The interface charge density engineering described here can be used to improve performance of device such as gate leakage and electron transport, and also provides a new design of normally-off MISHEMTs.

The density of two dimensional electron gas (2DEG) in the channel of AlGaN/GaN HEMT is often altered by trapped charges on the surface or in the bulk of the heterostructure, limiting the device performance at high frequencies. The existing methods, such as photoionization spectroscopy, Deep Level Transient Spectroscopy (DLTS) etc., mainly focus on deep level traps in GaN, providing little information about traps in the AlGaN layer. In this work, we use Inelastic Electron Tunneling Spectroscopy (IETS), in conjunction with the Frenkel-Poole (F-P) trap energy extraction method developed by Yeh at el, to examine electrically active traps in the AlGaN barrier layer. The results indicate that traps exist in the AlGaN bulk, as well as at the AlGaN/GaN interface. The trap energy levels are within a 0.5eV band below the conduction band edge (Ec) of AlGaN in the sample that we studied.

We report on the direct measurement of two-dimensional sheet charge density dependence of electron transport in AlGaN/GaN high electron mobility transistors. Pulsed IV measurements established increasing electron velocities with decreasing sheet charge densities, resulting in saturation velocity of 1.9 x 10^7 cm/s at a low sheet charge density of 7.8 x 10^11 cm-2. A new optical phonon emission-based electron velocity model for GaN is also presented. It accommodates stimulated LO phonon emission which clamps the electron velocity with strong electron-phonon interaction and long LO phonon lifetime in GaN. A comparison with the measured density-dependent saturation velocity shows that it captures the dependence rather well. Finally, the experimental result is applied in TCAD-based device simulator to predict DC and small signal characteristics of a reported GaN HEMT. Good agreement between the simulated and reported experimental results validated the measurement presented in this report and established accurate modeling of GaN HEMTs.

We report on the potential of high electron mobility transistors (HEMTs) consisting of high composition AlGaN channel and barrier layers for power switching applications. Detailed two-dimensional (2D) simulations show that threshold voltages in excess of 3 V can be achieved through the use of AlGaN channel layers. We also calculate the 2D electron gas mobility in AlGaN channel HEMTs and evaluate their power figures of merit as a function of device operating temperature and Al mole fraction in the channel. Our models show that power switching transistors with AlGaN channels would have comparable on-resistance to GaN-channel based transistors for the same operation voltage. The modeling in this paper shows the potential of high composition AlGaN as a channel material for future high threshold enhancement mode transistors.

Electrical properties of atomic layer deposited Al2O3/β-Ga2O3 interface were investigated. We determined the conduction band offset and interface charge density of Al2O3/β-Ga2O3 interface by analyzing the capacitance-voltage characteristics. The conduction band offset at the Al2O3/β-Ga2O3 interface was found to be 1.7 eV. A large positive sheet charge density of 3.6 × 1012 cm−2 is induced at the Al2O3/β-Ga2O3 interface, which caused a non-zero field of 0.7 MV/cm in the Al2O3 under flat-band conditions in the β-Ga2O3. The forward current-voltage characteristics were found to be related to trap-assisted tunneling.

We investigate the energy levels of electron traps in AlGaN/GaN high electron mobility transistors by the use of electron tunneling spectroscopy. Detailed analysis of a typical spectrum, obtained in a wide gate bias range and with both bias polarities, suggests the existence of electron traps both in the bulk of AlGaN and at the AlGaN/GaN interface. The energy levels of the electron traps have been determined to lie within a 0.5 eV band below the conduction band minimum of AlGaN, and there is strong evidence suggesting that these traps contribute to Frenkel-Poole conduction through the AlGaN barrier.

Characterization of Al2O3 gate dielectric on GaN using pulsed laser Atom Probe Tomography is reported. Atomic layer deposition was used to grow 5 nm of aluminum oxide on Ga-polar GaN. No oxidation of the surface of the semiconductor was observed and the interface was found to be non-abrupt. A significant amount of carbon impurities (1019/cm3) were detected in the dielectric film that matches well with the estimated bulk trap density from C–V measurements. Our experiments suggest possible correlation between trap-related electrical hysteresis and the observed impurity concentration in these films.

Interface charges at atomic layer deposited Al2O3/III-nitride interfaces were investigated for III-nitride layers of different polarity. A large positive sheet charge density is induced at the Al2O3/III-nitride interface on all the orientations of GaN and Ga-polar AlGaN, and this sheet charge can be significantly altered using post-metallization anneals. It is proposed that the charges are caused by interfacial defects that can be passivated and neutralized through a H2 based anneal. Tailoring of the interface charge density described here can be used to improve critical device characteristics such as gate leakage and electron transport, and for lateral electrostatic engineering.

Investigation of the properties of Al2O3-on-GaN metal-oxide-semiconductor diodes is reported. A new method is shown to calculate the metal-oxide barrier height based on the onset of the Fowler-Nordheim tunnelling current regime in direct bias. The Ni/Al2O3 barrier was extracted, for the first time with this method, and it was found to match other reports in the literature. The dependence of the effectiveness of this method on the oxide thickness is discussed. The breakdown field for Al2O3 was also measured and found to be in agreement with previous reports.

We report on the calculation of the two dimension electron gas (2DEG) mobility in scaled AlGaN/GaN metal-insulator-semiconductor high-electron-mobility-transistors. We investigate the effect of remote impurity and phonon scattering models on the 2DEG mobility of the dielectric/AlGaN/GaN structure and investigate its variation with dielectric/AlGaN interface charge density, 2DEG concentration, and AlGaN thickness. Remote impurity scattering was found to be the dominant mechanism when the 2DEG density is below 5 × 1012 cm−2 and dielectric/AlGaN interface charge density is above 5 × 1012 cm−2. The interfacial charge has significant effect on the mobility as the AlGaN cap layer thickness is scaled down below 5 nm.

We report on our investigation of the electrical properties of metal/Al2O3/GaN metal-insulator-semiconductor (MIS) capacitors. We determined the conduction band offset and interface charge density of the alumina/GaN interface by analyzing capacitance-voltage characteristics of atomic layer deposited Al2O3 films on GaN substrates. The conduction band offset at the Al2O3/GaN interface was calculated to be 2.13 eV, in agreement with theoretical predications. A non-zero field of 0.93 MV/cm in the oxide under flat-band conditions in the GaN was inferred, which we attribute to a fixed net positive charge density of magnitude 4.60x1012 cm-2 at the Al2O3/GaN interface. We provide hypotheses to explain the origin of this charge by analyzing the energy band line-up., 8 pages, 4 figures, Applied Physics Letters

The enhanced optical transmission through the annular aluminum metal with different number of concentric rings arranged in a long-range periodic structure on the silicon substrate is investigated. The measured transmission spectra demonstrate that the surface plasmon modes depend sensitively on the structural parameters of the metallic rings. The degenerate (1,0), (1,1), and (2,1) Al∕Si surface plasmon modes are determined by the long periodicity of the structure. The localized modes in cavities with different length can be observed in this structure as well. These phenomena suggest that both surface plasmons and localized cavity modes are excited within super unit cell.