Enhanced Electron Confinement Research Articles

Chemically functionalized AlN quantum dots for effective sensing and removal of methanol, ethanol, and formaldehyde: A first principle study

In this study, we delve into the structural and electronic intricacies of 2D aluminum nitride quantum dots (AlN-QDs) and their derivatives. Through detailed analysis, we uncover notable variations in bond lengths upon passivation with elements such as fluorine (F) and hydroxyl (OH) groups, with the latter exhibiting a particularly intriguing stability profile with a binding energy of 5.171 eV. Our investigation reveals a substantial energy gap of ∼5 eV in AlN-QDs, indicating enhanced electron confinement and optimal conditions for semiconductor applications. Furthermore, we elucidate the electron donation properties of nitrogen atoms and electron acceptance tendencies of aluminum atoms within AlN-QDs, shedding light on their unique electronic structure. Quantum stability assessments unveil charge distribution asymmetries and variations in electronegativity, contributing to a deeper understanding of AlN-QDs' robustness. We also demonstrate a significant enhancement in electrical conductivity, notably with AlN-QDs-surf-2CO exhibiting remarkable performance. Additionally, our study showcases AlN-QDs-OH's exceptional adsorption capabilities, evidenced by significantly higher adsorption energies for small organic compounds, highlighting their potential as highly effective sensors. Optical investigations further reinforce these findings, revealing distinct shifts in absorption spectra upon adsorption, which underscore the substantial impact of adsorbates on AlN-QDs' optical properties

Enhanced Electron Confinement of p-Block Indium Site in Extended Macrocyclic Conjugation Boosting Oxygen Reduction to Hydrogen Peroxide.

The electrocatalytic oxygen reduction reaction via a two-electron pathway (2e- ORR) is a promising route for hydrogen peroxide (H2O2) production. However, the strong electron interaction between the metal site and oxygen-containing intermediates usually generates 4-electron ORR, limiting H2O2 selectivity. Here, combining theoretical and experimental studies, we propose to enhance the electron confinement of the indium (In) center in an extended macrocyclic conjugation system toward high-efficiency H2O2 production. The extended macrocyclic conjugation in indium polyphthalocyanine (InPPc) evokes the attenuated transfer electron ability of the In center and weakens the interaction between the s orbital of In and the p obital of OOH*, favoring protonation of OOH* to H2O2. Experimentally, the prepared InPPc catalyst exhibits a noticeable H2O2 selectivity above 90% in 0.1-0.6 V vs RHE, outperforming the counterpart InPc. Importantly, the InPPc displays a high average H2O2 production rate of 23.77 mg/cm2/h in a flow cell. This study proposes a novel strategy to engineer molecular catalysts and provides new insights into the ORR mechanism.

In-Composition Graded Quantum Barriers for Polarization Manipulation in InGaN-Based Yellow Light-Emitting Diodes

Highly efficient indium gallium nitride (InGaN)-based yellow light-emitting diodes (LEDs) with low efficiency droop have always been pursued for next-generation displays and lighting products. In this work, we report an InGaN quantum barrier (QB) with linear-increase In-composition along [0001] direction for InGaN-based yellow LEDs. With the In-composition in QBs systematically engineered, three QB structures including linear-increase QB (LIQB), linear-decrease QB (LDQB) and commonly used flat QB (FQB) were investigated by simulation. The results show that the LIQB not only yields enhanced electron confinement, but also contributes to suppressed polarization field. Consequently, the yellow LED incorporated with LIQBs demonstrates improved radiative recombination rates and the efficiency droop is alleviated. Under a current density of 100 A/cm2, the efficiency droop ratios of LEDs with FQBs, LDQBs and LIQBs are 58.7%, 62.2% and 51.5%, respectively. When current density varies from 1 A/cm2 to 60 A/cm2, the blueshift values of peak emission wavelength for LEDs with FQBs, LDQBs and LIQBs are 14.4 nm, 16.5 nm and 13.0 nm, respectively. This work is believed to provide a feasible solution for high-performance InGaN-based LEDs in long-wavelength spectral region.

Effects of racetrack magnetic field strength on structure and properties of amorphous carbon coatings deposited by HiPIMS using deep oscillation pulses

In this study, non‑hydrogenated diamond like carbon (DLC) coatings were deposited by sputtering a graphite target in argon (Ar) by high power impulse magnetron sputtering (HiPIMS) using deep oscillation pulses. The effects of the magnetic field strength (B) tangential to surface of the target racetrack on the deposition parameters were studied. The structure, adhesion, and mechanical properties of DLC coatings deposited at different B were investigated by scanning electron microscopy (SEM), Raman spectroscopy, atomic force microscopy (AFM), scratch test, and nanoindentation. The tribological properties of the DLC coatings were evaluated using ball on disk wear test under dry and lubricated test conditions. It was found that the peak target current and substrate current density increased as B increased due to the enhanced electron confinement which results in an increased ionization efficiency. The enhanced ion bombardment was beneficial for improving the structure and properties of DLC coatings. As B increased, the DLC coatings exhibited more compact structure, smaller carbon mounds, and higher sp3 bond fractions. The improvement of the microstructure of the DLC coatings contributed to improved hardness and wear resistance of the coatings in both dry and lubricated test conditions. However, the deposition rate decreased at higher B owing to the high probability of back-attraction of carbon ions. The results suggested that controlling B in the range of 600 G to 700 G is important for achieving fully dense structure, high sp3 bond fractions, and high hardness for the DLC coatings deposited using HiPIMS. A further increase in B to 850 G showed no significant changes in the magnetic field induced effects on the structure and properties of the coatings.

Electrically injected GeSn lasers with peak wavelength up to 2.7 μm

GeSn lasers enable the monolithic integration of lasers on the Si platform using all-group-IV direct-bandgap material. The GeSn laser study recently moved from optical pumping into electrical injection. In this work, we present explorative investigations of GeSn heterostructure laser diodes with various layer thicknesses and material compositions. Cap layer material was studied by using Si 0.03 Ge 0.89 Sn 0.08 and Ge 0.95 Sn 0.05 , and cap layer total thickness was also compared. The 190 nm SiGeSn-cap device had threshold of 0.6 kA / cm 2 at 10 K and a maximum operating temperature ( T max ) of 100 K, compared to 1.4 kA / cm 2 and 50 K from 150 nm SiGeSn-cap device, respectively. Furthermore, the 220 nm GeSn-cap device had 10 K threshold at 2.4 kA / cm 2 and T max at 90 K, i.e., higher threshold and lower maximal operation temperature compared to the SiGeSn cap layer, indicating that enhanced electron confinement using SiGeSn can reduce the threshold considerably. The study of the active region material showed that device gain region using Ge 0.87 Sn 0.13 had a higher threshold and lower T max , compared to Ge 0.89 Sn 0.11 . The performance was affected by the metal absorption, free carrier absorption, and possibly defect density level. The maximum peak wavelength was measured as 2682 nm at 90 K by using Ge 0.87 Sn 0.13 in gain regions. The investigations provide directions to the future GeSn laser diode designs toward the full integration of group-IV photonics on a Si platform.

Composite‐channel In 0. 17 Al 0 . 83 N /In 0. 1 Ga 0 . 9 N / GaN /Al 0. 04 Ga 0 . 96 N high electron mobility transistors for RF applications

In this work, we present the high performance of composite channel based In0.17Al0.83N/In0.1Ga0.9N/GaN/Al0.04Ga0.96N high electron mobility transistors (HEMTs) on a sapphire substrate. A numerical simulation is carried out for the proposed and conventional GaN channel-based HEMTs using TCAD. Due to the strong polarization of InAlN/InGaN, enhanced electron confinement and high electron mobility of composite channel based proposed device shows excellent DC and RF characteristics with improved linearity than conventional GaN channel based HEMTs. A 55 nm T-gate device demonstrates 4.45 A/mm drain current density (IDS) at VGS = 0 V, 0.7 S/mm stable transconductance (GM) for a wide range of gate bias, and excellent FT/Fmax of 274/288 GHz. Benefiting from the Al0.04Ga0.96N buffer (back-barrier), the device shows a very low sub-threshold drain leakage current and high breakdown voltage (VBR) of 43.5 V. The combination of high FT/Fmax, stable transconductance, and high breakdown voltage of the proposed HEMTs shows the great promise for high power and wide-bandwidth millimeter-wave applications.

High performance InGaN double channel high electron mobility transistors with strong coupling effect between the channels

In this paper, high performance InGaN double channel (DC) high electron mobility transistors (HEMTs) are proposed and systematically investigated. Due to the coordination of double InGaN channels, a large maximum drain current density and a distinct double-hump feature of the transconductance and frequency performance are achieved. More importantly, it is revealed that the coupling effect between the two InGaN channels is much stronger than that of the conventional GaN DC HEMTs. This characteristic leads to a remarkable enhancement in the gate voltage swing, indicating the excellent linearity of the InGaN DC HEMTs at both dc and rf conditions. Benefiting from the enhanced electron confinement in InGaN channels, the fabricated HEMTs show a low off state drain leakage current of 0.26 μA/mm and a high on/off current ratio (Ion/Ioff) of 5.1 × 106. In addition, the desirable current collapse and breakdown characteristics are also obtained. This work convincingly demonstrates the great potential and practicality of the InGaN DC HEMTs for high power and high bandwidth applications.

Al0.3Ga0.7N/GaN (10 nm)/Al0.1Ga0.9N HEMTs With Low Leakage Current and High Three-Terminal Breakdown Voltage

In this work, we presented a high performance AlGaN/GaN/AlGaN double heterostructure HEMT with a 10 nm channel layer and an Al0.1Ga0.9N back barrier layer. The fabricated devices exhibited an extremely low off-state drain leakage current of ${I}_{ {\scriptscriptstyle {\text{ON}}}}/{I}_{ {\scriptscriptstyle {\text{OFF}}}}$ ) of up to 1010 and a subthreshold swing (SS) of 63 mV/dec were attained due to the reduced leakage current and enhanced electron confinement. The presented devices with a gate-drain spacing ( ${L}_{\text {GD}}$ ) of $22~\mu \text{m}$ exhibited a soft breakdown voltage ( ${V}_{\text {BR}}$ ) of 1860 V with the criteria of $0.1~\mu \text{A}$ /mm and a hard ${V}_{\text {BR}}$ of 2009 V combined with a specific on-resistance ( ${R}_{ {\scriptscriptstyle {\text{ON}}}, \text {sp}}$ ) of 10.6 $\text{m}\Omega \!\cdot \! \text {cm}^{{2}}$ . Moreover, excellent high-temperature values for ${I}_{ {\scriptscriptstyle {\text{ON}}}}/{I}_{ {\scriptscriptstyle {\text{OFF}}}}$ , SS, and ${V}_{\text {BR}}$ were also attained. These results demonstrate a promising potential of the proposed devices for high power applications.

Investigation of efficiency enhancement in InGaN MQW LED with compositionally step graded GaN/InAlN/GaN multi-layer barrier

The advantage of InGaN multiple Quantum well (MQW) Light emitting diode (LED) on a SiC substrate with compositionally step graded GaN/InAlN/GaN multi-layer barrier (MLB) is studied. The Internal quantum efficiency, Optical power, current-voltage characteristics, spontaneous emission rate and carrier distribution profile in the active region are investigated using Sentaurus TCAD simulation. An analytical model is also developed to describe the QW carrier injection efficiency, by including carrier leakage mechanisms like carrier overflow, thermionic emission and tunnelling. The enhanced electron confinement, reduced carrier asymmetry, and suppressed carrier overflow in the active region of the MLB MQW LED leads to render a superior performance than the conventional GaN barrier MQW LED. The simulation result also elucidates the efficiency droop behaviour in the MLB MQW LED, it suggests that the efficiency droop effect is remarkably improved when the GaN barrier is replaced with GaN/InAlN/GaN MLB barrier. The analysis shows a dominating behaviour of carrier escape mechanism due to tunnelling. Moreover, the lower lattice mismatching of SiC substrate with GaN epitaxial layer is attributed with good crystal quality and reduced polarization effect, ultimately enhances the optical performance of the LEDs.

Improving hole injection and carrier distribution in InGaN light-emitting diodes by removing the electron blocking layer and including a unique last quantum barrier

The effects of removing the AlGaN electron blocking layer (EBL), and using a last quantum barrier (LQB) with a unique design in conventional blue InGaN light-emitting diodes (LEDs), were investigated through simulations. Compared with the conventional LED design that contained a GaN LQB and an AlGaN EBL, the LED that contained an AlGaN LQB with a graded-composition and no EBL exhibited enhanced optical performance and less efficiency droop. This effect was caused by an enhanced electron confinement and hole injection efficiency. Furthermore, when the AlGaN LQB was replaced with a triangular graded-composition, the performance improved further and the efficiency droop was lowered. The simulation results indicated that the enhanced hole injection efficiency and uniform distribution of carriers observed in the quantum wells were caused by the smoothing and thinning of the potential barrier for the holes. This allowed a greater number of holes to tunnel into the quantum wells from the p-type regions in the proposed LED structure.

Advantages of blue InGaN light-emitting diodes without an electron-blocking layer by using AlGaN step-like barriers

With the purpose to increase the uniformity of carrier distribution without sacrificing the enhancement of carrier injection efficiency, the light-emitting diodes (LEDs) without an electron-blocking layer (EBL) by using AlGaN step-like barriers (SLBs) is proposed and investigated numerically. The simulation results show that the enhanced electron confinement and hole injection efficiency are mainly attributed to the mitigated downward band bending induced by polarization field at the interface of the last barrier and EBL and the increased carrier distribution uniformity is due to step-like potential height for carrier of the new designed LEDs. In addition, the distribution of radiative recombination rate and the efficiency droop are markedly improved when the conventional GaN barriers are replaced by AlGaN SLBs and the EBL is removed.

Investigation of blue InGaN light-emitting diodes with AlGaN barriers of the increasing Al composition

The characteristics of blue InGaN light-emitting diodes with AlGaN barriers of different step-like growth range Al composition and gradually increasing Al composition are investigated numerically. The simulation results indicate that the enhanced electron confinement and hole injection efficiency are mainly attributed to the mitigated downward band bending of the last barrier induced by polarization field, and the improved carrier distribution is owing to the increasing blocking for electrons as well as the decreasing blocking for holes. What's more, the output power, the distribution and rate of radiative recombination and the efficiency droop are markedly improved.

Efficiency droop improvement for InGaN-based light-emitting diodes with gradually increased In-composition across the active region

The gradually increased In-composition barriers were proposed to synthesize advantages of low polarization of InGaN barriers and high barrier height of GaN barriers. The reference structure with GaN barriers, the structure A with constant In-composition InGaN barriers and the structure B with gradually increased In-composition InxGa1−xN barriers were chosen. The light-emitting diodes were numerically studied. It is found that the structure B has the best performance. The output power is increased by 28% for structure B compared with structure A at 180mA. The improved performance is caused by the enhanced electron confinement and increased hole injection efficiency.

Investigation of ultraviolet optical properties of semiconducting-enriched and metal-enriched single-walled carbon nanotube networks using spectroscopic ellipsometry

The ultraviolet optical properties of semiconducting-enriched and metallic-enriched single-walled carbon nanotube (semi-enriched and m-enriched SWCNT) networks were studied using spectroscopic ellipsometry. According to calculated energy loss function, the energy loss peak assigned to the maximum intensity of π-plasmon energy was found to increase from 4.5 eV to 5.0 eV as SWCNT network composition was changed from m-SWCNT enriched to semi-SWCNT enriched. These results clearly demonstrate that the dielectric response in the 4-6 eV range is sensitive to changes in the surrounding dielectric environment depending on the semi-/m-SWCNT content. Therefore, the spectral shift of this energy loss is attributed to the enhanced electron confinement by the presence of the surface plasmon due to a small amount of m-SWCNT, which is an important phenomenon at the SWCNT network.

Room temperature InAs/InAs1−xSbx single quantum well light emitting diodes with barriers for improved carrier confinement

Room temperature InAs/InAs1−xSbx single quantum well light emitting diodes for the mid-infrared region that emit at λ∼4.2 μm with an internal efficiency of 2.6% and pulsed output powers of more than 110μW/A are studied. The structures are grown by molecular beam epitaxy and include an InAl0.17As0.83 barrier for enhanced electron confinement in the active region. Comparison with an identical structure grown without the barrier demonstrates an improvement in room temperature efficiency by a factor of more than six. Additional magneto-electroluminescence measurements reveal several very narrow subband transitions with a typical FWHM of only 10 meV. The broad (∼40 meV) LED emission spectra are therefore due to multiple bound states in the quantum wells. This shows the high material quality of the quantum wells, and that the quasi-Fermi energy separation, even at low (150 A/cm2) current densities, exceeds ∼30 meV and promises excellent prospects for high gain in laser diode structures made from these heterostructures.

Simple effective mass model to include the effects of GAMMA - X mixing in multiquantum barriers

An extended effective mass model is developed to account for the possibility of mixing of the electron wave function from the Γ conduction-band state to the X conduction-band state. The strength of the mixing is determined by a mixing parameter Δ in association with the assumption of a finite interface thickness. For a simple quantum well, the model Δ compares favorably with more complicated empirical pseudopotential models, featuring complete descriptions of the band structure. A multiquantum barrier (MQB) has been designed. Using the single-band effective mass approximation model, for use in visible laser diode structures for enhanced electron confinement, it is clear that within the limitations of the model when mixing effects are accounted for, the degradation in performance is negligible. The MOB design compared with a single barrier of equivalent thickness shows a doubling of the electron reflection coefficient.

CORDIS—an improved high-current ion source for gases

The multipole/reflex discharge ion source ELSIRE delivered high-current heavy ion beams (20–50 mA) of low emittance, but with poor power- and gas-efficiencies. Therefore, a new version of the source, CORDIS, was constructed, based on the same discharge principle. The diameter of the discharge chamber was doubled, compared to ELSIRE, thus allowing enlarged extraction areas. At the same time, a modified magnetic multipole field leads to enhanced electron confinement, while a shift of the extraction plane increases the effective plasma density. The measurements show a reduction of discharge power and gas pressure by a factor of ten. Thus reliability and life-time are much improved and dc operation has also become possible. With 1.3 kW dc discharge power, the source life-time exceeds 80 h. Several test runs with single- and multi-aperture extraction systems will be discussed. The most prominent result amounts to 71 mA for xenon ions or 814 (mA) normalized current (proton equivalent).