Aluminum Oxide Passivation Layer Research Articles

Influence of Process Conditions During Aqueous and Direct Recycling of NMC811 Cathodes.

This study investigated the impact of various process conditions on the aqueous, direct recycling of LiNi0.8Mn0.1Co0.1O2 (NMC811) cathodes. Three model systems were used. The first system assumes that the current collector delamination is performed in a dry environment without the use of water as a process medium. Consequently, the NMC811 is only exposed to water during classification, where no aluminum foil is present. The second model system assumes that the current collector delamination occurs in water. Therefore, the NMC811 is exposed to water in the presence of aluminum foil. Due to the pH increase caused by the Li+/H+ exchange reaction, the pH value surpasses the stability window of the aluminum-oxide passivation layer (pH 4.5-8.5), resulting in the deposition of aluminum-containing species on the NMC811 surface. The third model system is identical to the second, with the exception that H3PO4 is added. This causes the pH to decrease and prevents corrosion of the aluminum foil. The findings reveal that process conditions significantly affect the surface chemistry on NMC811, influencing electrochemical performance. Notably, aluminum-containing species increase polarization. Heat treatment simulating regeneration led to cation mixing as surface species diffused into the NMC811 bulk structure, highlighting the need to control recycling process conditions.

Effect of annealing on MoOx and interface properties for carrier-selective contact solar cells with different passivation layers

The structural, electrical and optical properties of molybdenum oxide (MoOx) thin films prepared by magnetron sputtering are studied with annealing temperature. The interface properties of silicon with the intrinsic amorphous silicon (a-Si:H(i)) and alumina (AlOx) passivation layers are investigated by the minority carrier lifetime and implied-Voc (iVoc). The AlOx shows the better passivation properties and thermal stability for the carrier-selective contact solar cells. The Ce-doped In2O3(ICO) is deposited on the surface of MoOx thin films. It is found that the optimized annealing temperature is 125 °C for the carrier selective contact solar cells with the a-Si:H(i) passivation layer. It could increase to 175 °C for the AlOx passivation layer.

Passivated indium oxide thin-film transistors with high field-effect mobility (128.3 cm2 V−1 s−1) and low thermal budget (200 °C)

Here, we demonstrate a high-mobility indium oxide (In2O3) thin-film transistor (TFT) with a sputtered alumina (Al2O3) passivation layer (PVL) with a low thermal budget (200 °C). The sputtering process of the Al2O3 PVL plays a positive role in improving the field-effect mobility (µ FE) and current on/off ratio (I ON/I OFF) performance of the In2O3 TFTs. However, these enhancements are limited due to the high density of intrinsic trap defects in the In2O3 channels, as reflected in their large hysteresis and poor bias stability. Treating the In2O3 channel with oxygen (O2) plasma prior to sputtering the Al2O3 PVL results in notable improvements. Specifically, a high µ FE of 128.3 cm2V−1 s−1, a high I ON/I OFF over 106 at V DS of 0.1 V, a small hysteresis of 0.03 V, and a negligible threshold voltage shift under negative bias stress are achieved in the passivated In2O3 TFT (with O2 plasma pretreatment), representing a significant improvement compared to the passivated In2O3 TFT (without O2 plasma pretreatment) and the unpassivated In2O3 TFT. The remarkable reduction of intrinsic trap defects in the passivated In2O3 TFT compensated by O2 plasma is the primary mechanism underlying the improvement in µ FE and bias stability, as validated by x-ray photoelectron spectra, hysteresis analysis, and temperature-stress electrical characterizations. Plasma treatment effectively compensates for intrinsic trap defects in oxide semiconductor (OS) channels, when combined with sputter passivation, resulting in a significant enhancement of the overall performance of OS TFTs under low thermal budgets. This approach offers valuable insights into advancing OS TFTs with satisfactory driving capability and wide applicability.

A Non-Flammable and Flexible Aluminum Derived Lithium-Ion Storage Device with a Wide Temperature Range of Operation.

With the rapid development and increasing popularity of electric vehicles and wearables, battery safety has become a leading focus in the field of energy storage research. Specifically, aluminum-ion batteries are gaining increasing attention as low-cost energy-storage systems with high safety levels and theoretical energy density. However, the dense alumina passivation layer on the aluminum anode surface and slow kinetic performance of commonly used ionic liquid electrolytes still render poor performance. This report presents a new type of aluminum-derived lithium-ion battery (ALIB) that maintains a certain discharge performance under damaging conditions, including continuous bending, high- and low-temperature environments, and shearing. This new ALIB effectively meets the current demand for flexible and wearable batteries. The prepared ALIB achieves a stable cycle of 130 mAh g-1 specific capacity and ≈260Wh kg-1 theoretical energy density at a wide voltage platform of 2V and a test temperature of 25 °C without undergoing combustion. Additionally, the study analyzes the reaction mechanism of this ALIB based on density functional theory and conducts ex situ XRD and XPS analyses to elucidate the underlying storage mechanism.

Passivation-Free, Liquid-Metal-Based Electrosynthesis of Aluminum Metal-Organic Frameworks Mediated by Light Metal Activation.

The production of aluminum (Al) metal-organic frameworks (MOFs) by electrosynthesis using solid-state Al electrodes always faces significant challenges due to the formation of a passivating aluminum oxide layer in the process. Here, we developed a liquid-metal-based method to electrosynthesize an aluminum Al-MOF (MIL-53). This method uses a liquid-state gallium (Ga) anode as a reservoir and activator for a light metal, Al, in the form of Al-Ga alloys that releases Al3+ for the electrosynthesis of Al-MOFs. Introducing Ga into the system inhibits the formation of aluminum oxide passivation layer and promotes the electrochemical reaction for Al-MOF synthesis. The electrosynthesis using liquid Al-Ga alloy is conducted at ambient temperatures for long durations without requiring pretreatment for aluminum oxide removal. We show that the Al-MOF products synthesized from 0.40 wt % Al in liquid Ga lead to the highest crystallinity and possess a specific surface area greater than 800 m2 g-1 and a low capacity for CO2 adsorption that can be used as a potential matrix for CO2/N2 separation. This work provides evidence that employing liquid-metal electrodes offers a viable pathway to circumvent surface passivation effects that inevitably occur when using conventional solid metals. It also introduces an efficient electrosynthesis method based on liquid metals for producing atomically porous materials.

Enhancing electrical performance and stability of nanometer-thin ITO transistors via thermally oxidized alumina passivation layer

In this study, we investigated the utilization of alumina (AlOx), formed through the oxidation of thermally evaporated aluminum, as a passivation layer for nanometer-thin indium-tin-oxide (ITO) transistors. The ITO transistors passivated with thermally oxidized AlOx passivation exhibited remarkable electrical properties, with an average field-effect mobility of 241 cm2/Vs, significantly higher than the 40 cm2/Vs observed for devices without the AlOx passivation layer. Moreover, the passivated transistors maintained a high on/off current ratio at 108 level. In addition, the passivated transistors demonstrated improved stability, with a decrease in the threshold voltage (Vth) shift under negative bias stress testing conducted over 3600 seconds. The ITO transistors also displayed better air-ambient stability compared to transistors without the AlOx passivation layer. These results demonstrate the potential application of alumina passivation in nanometer-thin ITO field-effect transistors.

Exotic Inverse Kinetic Isotopic Effect in the Thermal Decomposition of Levitated Aluminum Iodate Hexahydrate Particles

Aluminum iodate hexahydrate ([Al(H2O)6](IO3)3(HIO3)2; AIH) represents a novel, oxidizing material for energetic applications. Recently, AIH was synthesized to replace the aluminum oxide passivation layer of aluminum nanoenergetic materials (ALNEM). The design of reactive coatings for ALNEM-doped hydrocarbon fuels in propulsion systems requires fundamental insights of the elementary steps of the decomposition of AIH. Here, through the levitation of single AIH particles in an ultrasonic field, we reveal a three-stage decomposition mechanism initiated by loss of water (H2O) accompanied by an unconventional inverse isotopic effect and ultimate breakdown of AIH into gaseous elements (iodine and oxygen). Hence, AIH coating on aluminum nanoparticles replacing the oxide layer would provide a critical supply of oxygen in direct contact with the metal surface thus enhancing reactivity and reducing ignition delays, further eliminating decades-old obstacles of passivation layers on nanoenergetic materials. These findings demonstrate the potential of AIH to aid in the development of next-generation propulsion systems.

(Digital Presentation) Characterization of Passivation Dielectrics on Silicon Through Second Harmonic Generation: Effect of Fixed Charge

This paper presents the characterization of alumina passivation layers using second harmonic generation (SHG). Based on nonlinear optics, the technique has the advantage of being rapid and non-destructive, especially for thin oxide layers. For the materials under study, the SHG is sensitive to the electronic and structural properties of the interface, particularly to the interfacial electric field (Edc), and thus allowing to characterize fixed oxide charges (Qox) in the oxide and interface traps density (Dit). Time-dependent SHG (TD-SHG) is firstly used here to probe samples with various Dit and a total oxide charges (Qtot), previously extracted using corona oxide characterization of semiconductor (COCOS). The measurement conditions are adjusted to focus on the impact of the fixed charges on the SHG signal. A more detailed analysis of the SHG versus input polarization is conducted in both experiments and simulations and it shows coherent evolution tendencies with the oxide charge.

PMMA/Al2O3 bilayer passivation for suppression of hysteresis in chemically doped carbon nanotube thin-film transistors

Hysteresis is usually present in carbon nanotube thin-film transistors exposed to air due to adsorbed water and oxygen molecules. Thus, it is desirable to passivate the device from these environmental effects and provide an air-stable platform for chemical doping to tune the threshold voltages. Here, we demonstrate p- and n-doped carbon nanotube transistors with suppressed hysteresis using bilayer stacking of poly(methyl methacrylate) and aluminum oxide (Al2O3) passivation layers using a low-temperature process suitable for flexible substrates. The results show that the bilayer passivation layers achieved reduced hysteresis to be 2.25% of applied gate voltage at low operation voltage as 2 V.

Study on Annealing Process of Aluminum Oxide Passivation Layer for PERC Solar Cells

In this study, Atomic Layer Deposition (ALD) equipment was used to deposit Al2O3 film on a p-type silicon wafer, trimethylaluminum (TMA) and H2O were used as precursor materials, and then the post-annealing process was conducted under atmospheric pressure. The Al2O3 films annealed at different temperatures between 200–500 °C were compared to ascertain the effect of passivation films and to confirm the changes in film structure and thickness before and after annealing through TEM images. Furthermore, the negative fixed charge and interface defect density were analyzed using the C-V measurement method. Photo-induced carrier generation was used to measure the effective minority carrier lifetime, the implied open-circuit voltage, and the effective surface recombination velocity of the film. The carrier lifetime was found to be the longest (2181.7 μs) for Al2O3/Si post-annealed at 400 °C. Finally, with the use of VHF (40.68 MHz) plasma-enhanced chemical vapor deposition (PECVD) equipment, a silicon nitride (SiNx) film was plated as an anti-reflection layer over the front side of the wafer and as a capping layer on the back to realize a passivated emitter and rear contact (PERC) solar cell with optimal efficiency up to 21.54%.

Design of Grating Al2O3 Passivation Structure Optimized for High-Efficiency Cu(In,Ga)Se2 Solar Cells.

In this paper, we propose an optimized structure of thin Cu(In,Ga)Se2 (CIGS) solar cells with a grating aluminum oxide (Al2O3) passivation layer (GAPL) providing nano-sized contact openings in order to improve power conversion efficiency using optoelectrical simulations. Al2O3 is used as a rear surface passivation material to reduce carrier recombination and improve reflectivity at a rear surface for high efficiency in thin CIGS solar cells. To realize high efficiency for thin CIGS solar cells, the optimized structure was designed by manipulating two structural factors: the contact opening width (COW) and the pitch of the GAPL. Compared with an unpassivated thin CIGS solar cell, the efficiency was improved up to 20.38% when the pitch of the GAPL was 7.5–12.5 μm. Furthermore, the efficiency was improved as the COW of the GAPL was decreased. The maximum efficiency value occurred when the COW was 100 nm because of the effective carrier recombination inhibition and high reflectivity of the Al2O3 insulator passivation with local contacts. These results indicate that the designed structure has optimized structural points for high-efficiency thin CIGS solar cells. Therefore, the photovoltaic (PV) generator and sensor designers can achieve the higher performance of photosensitive thin CIGS solar cells by considering these results.

Novel cost-effective approach to produce nano-sized contact openings in an aluminum oxide passivation layer up to 30 nm thick for CIGS solar cells

This work presents a novel method of local contact openings formation in an aluminum oxide (Al2O3) rear surface passivation layer by the selenization of the lithium fluoride (LiF) salt on top of the Al2O3 for ultra-thin copper indium gallium (di)selenide (CIGS) solar cells (SCs). This study introduces the potentially cost-effective, fast, industrially viable, and environmentally friendly way to create the nano-sized contact openings with the homogeneous distribution in the thick, i.e. up to 30 nm, Al2O3 passivation layer. The passivation layer is deposited by atomic layer deposition, while the LiF layer is spin-coated. Selenization is done in the H2Se atmosphere and the optimal process parameters are deduced to obtain nano-sized and uniformly allocated openings as confirmed by scanning electron microscopy images. The contact openings were produced in the different thicknesses of the alumina layer from 6 nm to 30 nm. Furthermore, the Al2O3 rear surface passivation layer with the contact openings was implemented into ultra-thin CIGS SC design, and one trial set was produced. We demonstrated that the created openings facilitate the effective current collection through the dielectric Al2O3 layer up to 30 nm thick. However, the upper limit of Al2O3 thickness in which the contact openings can be created by the described method is not established yet. The produced passivated CIGS SCs show increased external quantum efficiency response due to the optical enhancement of the passivated cells. However, the production of SCs on the Al2O3 passivation layer with the openings created by selenization of LiF is not optimized yet.

AC-coupled n-in-p pixel detectors on MCz silicon with atomic layer deposition (ALD) grown thin film

We report initial characterization of our novel sensor process solutions with AC-coupled n+/p−/p+ pixel detectors made on 150 mm diameter p-type Magnetic Czochralski silicon (MCz-Si) wafers. The pixels were segmented in a 52 × 80 dual column array and designed to be AC capacitive coupled. The resistive coupling between pixels, allowing quality assurance probing prior the flip chip bonding, was realized with thin film metal-nitride resistors fabricated by sputtering deposition. This approach allows us to omit punch-through resistor structures, which reduces the overall process complexity. Moreover, our previous studies have emphasized that applying ALD Aluminum Oxide (Al2O3) field insulator and passivation layer results in negative net oxide charge and thus additional p-spray or p-stop surface current termination structures are not necessary. Our focused application is a radiation-hard ALD AC-coupled pixel detector to be used in future particle physics experiments, such as the High-Luminosity Large Hadron Collider (HL-LHC), as well as photon counting applications. The pixel detectors were tested at Helsinki Institute of Physics (HIP) Detector laboratory and Ruđer Bošković Institute (RBI). We show measurement data of pixel detectors and other test structures. For the TiN resistors surrounding pixels, the resistance values were measured to be about 15kΩ. Data of electrical properties, full depletion voltage and leakage current are shown as well. Our Transient Current Technique (TCT) measurements indicated clear pixel segmentation with excellent homogeneity. For further study, AC-coupled sensors were hybridized to PSI46dig read out chips (ROC) by flip-chip interconnection technique and tested with a radioactive source.

Spatial Atomic Layer Deposition of Aluminum Oxide as a Passivating Hole Contact for Silicon Solar Cells

Herein, tunneling aluminum oxide (Al2O3) passivation layers are demonstrated to be a candidate for hole collecting, passivating contacts when coupled with a boron‐doped surface. These very thin Al2O3 films (1.5–3 nm) are deposited using spatial atomic layer deposition (ALD) on boron diffused (110–115 Ω □−1) hydrophilic surfaces operating as metal–insulator–semiconductor (MIS) contacts. The emitter saturation current density values of ≈57 fA cm−2 are achieved for the Al2O3 film thicknesses of 2 nm before metallization. At this same thickness, the contact resistivity values of 33 mΩ cm2 are obtained after metallization. Most importantly, the boron diffusion, wet chemical surface preparation, and spatial ALD of Al2O3 used to create these MIS structures are all performed with industrially relevant equipment on Cz wafers.

Improving the Passivation of Molybdenum Oxide Hole‐Selective Contacts with 1 nm Hydrogenated Aluminum Oxide Films for Silicon Solar Cells

Silicon Solar Cells Precisely inserting hydrogen in few monolayer aluminum oxide passivation layer during atomic layer deposition (ALD) can lead to carrier lifetimes of over one millisecond. Coupling this layer with an ALD hole-selective molybdenum oxide film results in a low resistivity, fully transparent, passivating hole contact. This film stack can be integrated in highly efficient silicon solar cells. More details can be found in article number 2000093 by Kristopher O. Davis and co-workers.

(Invited) Rare Earth Doped Layers Fabricated By Atomic Layer Deposition

Many approaches, developments, structures and materials have been proposed these last years to offer innovative solutions allowing the decrease of the CO2 production and the energy consumption while increasing the efficiency of the properties which are aiming for. Over the last decade, among the approaches developed, a growth process has experienced an important boom related to the possibility it offers on the development of high quality layers. It concerns the Atomic Layer Deposition technique (ALD) that allows growing conformal layer on a substrate having high surface/volume ratio. Although such a technique is well developed and used for microelectronic and photovoltaic applications, the works on photonic devices are still at an early stage. Indeed, for the former, Al2O3, SiNx, HfO2 materials are currently deposited using ALD for microelectronic devices. Besides, the high quality alumina passivation layer is deposited on the Si solar cell bottom that allows the increase of the performance of the solar cell. However, for photonic devices, the crucial issue is to succeed in incorporating and managing the dopant concentration during the process.ALD process is a, at least, two steps process requiring a precursor containing the element of the layer to grow and oxidation step. The most used sequence for Al2O3 growth is a trymethylaluminium (TMA) precursor pulse followed by an oxidation step using water pulse. For doping such layer, a suitable precursor allowing to grow a dopant atomic layer in a temperature range and under oxidizing conditions that are appropriate with the host matrix growth has to be found.The objective of this paper is to present our recent investigations on the growth of RE-doped Al2O3 layer by ALD using different RE precursors. For growing such doped layer, four steps process is required corresponding to the TMA precursor/oxidation sequence followed by the RE-precursor/oxidation one. Fabrication conditions using either water, O2 plasma or ozone as oxidant agent have been investigated to find the ALD window leading to a suitable Growth Per Cycle (GPC) rate in a low deposition temperature range. After deposition, different annealing treatments have been applied to optimize the microstructural and the optical properties of the films considering their potential application, notably in photovoltaic domain. The most attention was paid to Tb- and Er-doped Al2O3 thin layers growth and to the optimization of the processing conditions to achieve required optical properties for the photon management in solar cell.As an example, Er-doped Al2O3 layers have been produced varying the number of Er precursor cycles with respect to the TMA one in order to manage the Er concentration in the layer. Our thin films containing 4.0 to 13 at.% of Er in the host matrix were found to be homogeneous not only prior to the annealing treatment but also after an annealing at 650°C during 15 minutes in nitrogen, conditions that are suitable for solar cell processing. For the highest concentration, phase separation has been observed upon annealing temperature at high temperature. Photoluminescence and photoluminescence excitation experiments have been carried out to study the optical response of such a layer. Indeed, considering that 100nm-thick Al2O3 ALD layer is actually used at the bottom of the Si Cell, succeeding to incorporate optically active Er ions in such a layer and achieving an upconversion process to convert the IR non-absorbed photons by the cell would be a way to increase the Si cell efficiency without modifying a well-established industrial process.

Aluminium oxide passivation films by liquid phase deposition for TiO2 ultraviolet solid–liquid heterojunction photodetectors

In this study, an aluminum oxide passivation layer generated through liquid-phase deposition (LPD) was used to improve the properties of a TiO2 ultraviolet solid–liquid heterojunction photodetector. An aluminum oxide deposition solution was used to reduce the oxygen vacancies of TiO2. Moreover, the surface roughness and porosity of the TiO2 film improved after aluminum oxide deposition. An aluminum oxide passivation layer was deposited on a TiO2/indium-tin-oxide (ITO)/glass photodetector with the precursors of aluminum sulfate and sodium bicarbonate. The responsivity and turn-off time of the TiO2/ITO photodetector were 133 mA/W and 34.6 s, respectively. A dense and uniform film surface could be obtained after the aluminum oxide passivation layer was deposited on TiO2 to form an Al2O3–TiO2 composite film. After deposition, the responsivity and turn-off time improved to 208 mA/W and 27.3 s, respectively. Thus, the LPD passivation film is highly favorable for improving the properties of photodetectors.

Ultrathin Al2O3 passivation layer-wrapped Ag@TiO2 nanorods by atomic layer deposition for enhanced photoelectrochemical performance

In this study, new one-dimensional (1D) titanium dioxide nanorod (TONR) array films sensitized with Ag nanoparticles (ANPs) and coated with ultrathin alumina (Al2O3) passivation layer were synthesized. ANPs and Al2O3 passivation layer were deposited via magnetron sputtering technology and atomic layer deposition (ALD) method, respectively. The morphology, structure, composition, optical properties, and PEC properties on varied amounts ANPs and tailored Al2O3-modulated TONR films were investigated systematically. The results exhibited that with an optimal thickness of the Al2O3 layer and a suitable sputtering time of ANPs, the TONR arrays can effectively restrain the recombination of electron-holes and improve the PEC performance. Furthermore, 20 cycles of Al2O3 passivation on Ag10@TONR shows the optimal PEC performance with the maximum photocurrent density (~0.34 mA/cm2), which is almost 5 times higher than that of Ag10@TONR (~56.9 μA/cm2) and 30 times as much as that of pure TONR (~11.3 μA/cm2). The superior PEC performance of Al2O3-Ag@TONR is ascribed to the local surface plasmon resonance (LSPR) effect of ANPs, and the passivation effect of the Al2O3 coating layer.

Size effects in the resistivity of graphene nanoribbons

The electrical resistivity of single-layer graphene nanoribbons has been studied experimentally for ribbon widths from 16 to 320 nm and is shown to validate the expected quantum scattering model for conduction through confined graphene structures. The experimental findings are that the resistivity follows a more dramatic trend than that seen for metallic nanowires of similar dimensions, due to a combination of the nature of the charge carriers in this 2D material, surface scattering from the edges, bandgap related effects and shifts in the Fermi level due to edge effects. We show that the charge neutrality point switches polarity below a ribbon width of around 50 nm, and that at this point, the thermal coefficient of resistance is a maximum. The majority doping type therefore can be controlled by altering ribbon width below 100 nm. We also demonstrate that an alumina passivation layer has a significant effect on the mean free path of the charge carriers within the graphene, which can be probed directly via measurements of the width-dependent resistivity.

Effect of Hydration on Promoting Oxidative Reactions with Aluminum Oxide and Oxyhydroxide Nanoparticles

To harness greater power from aluminum (Al) combustion, one approach is to chemically transform the aluminum oxide (Al2O3) passivation layer surrounding the Al core particle by exploiting surface r...