Al2O3 Passivation Layer Research Articles

Bias-controlled photocurrent generation process in GaN-based ultraviolet p–i–n photodetectors fabricated with a thick Al2O3 passivation layer

GaN-based p–i–n ultraviolet photodetectors (UV-PDs) with a 20 nm thick Al2O3 passivation layer are fabricated and the photocurrent generation mechanisms of the device at different biases are studied by performing different electro-optical measurements. Our UV-PDs reveal good rectifying current–voltage behavior but their generated photocurrent to UV light varies sub-linearly with the impinging power. This sub-linear trend is ascribed to the effect of strong carrier trapping. Furthermore, in reverse bias mode, PDs show higher photocurrent than forward bias, suggesting the higher charge carrier separation process caused by the exacerbated electric field. The simulated results are also agreed well with the experimental observations.

Cyclic Thermal Effects on Devices of Two‐Dimensional Layered Semiconducting Materials

AbstractField‐effect transistors (FETs), using transition metal dichalcogenides (TMD) as channels, have various types of interfaces, and their characteristics are sensitively changed in temperature and electrical stress. In this article, the effect of fast cyclic thermal stress on the performance of FETs using TMD as a channel is investigated and introduced. The Al2O3 passivation layer is deposited onto the TMD channel by atomic layer deposition process, and the hysteresis decreases and the direction changes from clockwise to counterclockwise. Applying cyclic thermal stress that rapidly heats and cools by 90 K in a 20 s cycle increases and decreases drain current repeatedly as charges move between the TMD channel and the interface traps. As cyclic thermal stress is applied, permanent interfacial damage occurs, resulting in increased interface trap density at the bottom and decreased hysteresis. These experimental results are also shown through technology computer‐aided design simulations. In addition, series resistance and mobility attenuation factor increase due to the concentration of the conduction paths at the bottom of the channel.

Investigation on Al3+ and Al2O3 Coexist in BiVO4 for Efficient Methylene Blue Degradation: Insight into Surface States and Charge Separation.

A series of Al-doped BiVO4 composites have been synthesized via the hydrothermal method for methylene blue (MB) degradation application. The reasons for the improvement of photocatalytic performance was explained from the perspective of optics. Transient photovoltage (TPV) measurements suggested that the surface states have the priority to capture photogenerated carriers, and the Al2O3 surface passivation layer can prolong the lifetime of charge carrier. The results of surface photovoltage (SPV), transient photovoltage (TPV), and surface photocurrent (SPC) measurements suggested that the coexistence of Al3+ and Al2O3 caused by the appropriate doping would improve the transfer property and prolong the lifetime of photogenerated carriers. Finally, the possible photocatalytic mechanism is expounded to illustrate the photogenerated charge behavior under visible light irradiation. This work provides a better understanding of the synergistic effect of Al-doping and Al2O3 passivation layer on enhancing the photocatalytic performance.

Radiation hardened H-diamond MOSFET (RADDFET) operating after 1 MGy irradiation

Although the surface conductivity of a hydrogen-terminated diamond (H-diamond) enables production of high-performance field effect transistors (FETs), the total ionizing dose effect is yet to be clarified for H-diamond FETs. We fabricated a RADiation hardened H-terminated Diamond metal–oxide–semiconductor FET (RADDFET) using an oxide gate dielectric deposited at high temperatures. This paper describes its stable operation after 1 MGy irradiation. H-diamond films were prepared using microwave plasma assisted chemical vapor deposition with a p+ layer for reduction of contact resistance. The Al2O3 passivation layer was deposited by atomic layer deposition at 450 °C to achieve operation in high-temperature environment; then a RADDFET was fabricated on them using a Ru electrode. Several current–voltage characteristics were compared before irradiation and after certain dose levels up to 1 MGy. Before they were irradiated in air, the dose rate was measured using a cellulose triacetate film dosimeter. Even after an irradiation level of 1 MGy, the off-current at gate bias voltage (VG) of 3 V was more than six orders of magnitude lower than the on-current at VG of −6 V. Variation of the drain current density (JDS) in the measurements was less than 2%. The threshold voltage shifted approximately 1.7 V with 3 kGy of x ray irradiation, but no marked degradation was confirmed at higher levels. The subthreshold swings were 238, 215, and 264 mV/decade, respectively, after irradiation of 100 kGy, 300 kGy, and 1 MGy. These results indicate that the RADDFET was very stable at higher doses after initial stabilization.

Reliability study on deep-ultraviolet photodetectors based on ZnGa2O4 epilayers grown by MOCVD

Deep ultra-violate (DUV) photodetectors (PDs) fabricated by ZnGa2O4 thin film with back-to-back Schottky type metal–semiconductor-metal (MSM) structure have been studied and presented a superior performance. To further discuss the reliability of DUV device should be the pivot for the DUV application. We were using an accelerating life test (ALT) for UVC PDs by applied in monitoring sterilization light sources during this research. After ALT for one week, the device showed low reliability with a varying current level, and the change of response time and rejection ratio are enormous. Following the XRD and XPS results, we find out that the reliability issue is caused by the surface water adsorption and ozone compensation. Furthermore, the 45-nm-thick Al2O3 passivation layer was deposited by atomic layer deposition (ALD) for isolating the effect of the atmosphere. It resulted in increasing the stability of the current level and reducing the response time for the DUV PDs.

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.

A Three-Dimensional Branched TiO2 Photoanode with an Ultrathin Al2O3 Passivation Layer and a NiOOH Cocatalyst toward Photoelectrochemical Water Oxidation.

Photoelectrochemical (PEC) water splitting provides an alternative strategy for clean and renewable hydrogen production; however, the practical application is severely limited by the low solar conversion. Herein, a novel and simple strategy has been developed to construct a 3D branched TiO2 photoanode with an ultrathin Al2O3 passivation layer and NiOOH cocatalyst. The structure and properties of the as-obtained photoanodes are explored by X-ray diffraction, Mott-Schottky, electrochemical impedance spectroscopy, and open circuit voltage measurements. The as-obtained B-TiO2/Al2O3/NiOOH ternary heterojunction with a high-quality contact interface exhibits improved light absorption ability, an enhanced photocurrent density of 1.42 mA/cm2 at 1.23 VRHE, high conversion efficiency (0.44% at 0.80 VRHE), and excellent stability compared to pristine TiO2 and alone-Al2O3 or NiOOH decorated TiO2 photoanodes. Therefore, this work could offer a new approach to designing and fabricating high-quality contact interfaces between photoelectrodes and various cocatalysts.

Role of an Al2O3 Passivation Layer during Annealing of 2D-SnS2 Thin Films Grown by Atomic Layer Deposition

Tin disulfide (SnS2) is a two-dimensional (2D) post-transition metal chalcogenide (p-TMDC) with considerable potential to compete with other benchmarked 2D-TMDC materials such as MoS2 and WS2. Compared with other 2D-TMDC materials, SnS2 has the strong advantage of being synthesized at low temperature. However, a lower synthetic temperature of SnS2 lessens its thermal stability at high temperature. Thus, many researchers have cautiously handled SnS2 when exposing it to high process temperature. In this paper, 2D SnS2 thin films with and without an Al2O3 passivation layer were prepared by atomic layer deposition (ALD), and post-annealing was performed under a H2S environment at various temperatures. SnS2 thin film with an Al2O3 passivation layer is more thermally stable at higher temperature during post-annealing than is SnS2 thin film without an Al2O3 passivation layer. Furthermore, higher temperatures used during post-annealing facilitate enhanced crystallinity of 2D SnS2 thin films without evaporation. The enhanced crystallinity is mainly attributed to the presence of an Al2O3 passivation layer that blocks evaporation of SnS2 and enables increased processing temperature in post-annealing.

Improving photovoltaic properties of ZTO-based DSSCs using surface modification of Zn2SnO4 nanoparticles prepared by co-precipitation method

We synthesized high-quality Zn2SnO4 nanoparticles via simple co-precipitation method and crystallinity along with phase purity of resultant nanopowders were increased by applying different values of pH, precursor concentrations, and annealing temperatures. After that, the crystalline Zn2SnO4 nanoparticles with an average size of about 35 nm were used as a mesoporous layer and then modified by using MgO and Al2O3 passivation layers. We optimized the thickness of these barrier layers with controlling the concentration of solution and velocity of the spin-coating process which had a vital role in suppressing recombination and significantly enhanced performance of DSSCs. The highest electronic parameters of JSC=8.59 mA/cm2, VOC=0.66 V, and FF=0.51 were obtained for the MgO-treated device (with rotation speed of 4000 rpm) that showed 40% increment in the efficiency from 2.07% to 2.90% compared to the untreated sample. The improvement of VOC was observed in all treated samples that attribute to an upward shift of the Zn2SnO4 flat band energy and could be explained by the blocking effect of the interfacial layer. Further investigation through the transport and recombination mechanisms were carried out by electrochemical impedance spectroscopy, open-circuit voltage decay, and dye-loading process, which confirmed faster transport rate and slower electron recombination in the most modified devices.

Role of ALD Al2O3 Surface Passivation on the Performance of p-Type Cu2O Thin Film Transistors.

High-performance p-type oxide thin film transistors (TFTs) have great potential for many semiconductor applications. However, these devices typically suffer from low hole mobility and high off-state currents. We fabricated p-type TFTs with a phase-pure polycrystalline Cu2O semiconductor channel grown by atomic layer deposition (ALD). The TFT switching characteristics were improved by applying a thin ALD Al2O3 passivation layer on the Cu2O channel, followed by vacuum annealing at 300 °C. Detailed characterization by transmission electron microscopy-energy dispersive X-ray analysis and X-ray photoelectron spectroscopy shows that the surface of Cu2O is reduced following Al2O3 deposition and indicates the formation of a 1-2 nm thick CuAlO2 interfacial layer. This, together with field-effect passivation caused by the high negative fixed charge of the ALD Al2O3, leads to an improvement in the TFT performance by reducing the density of deep trap states as well as by reducing the accumulation of electrons in the semiconducting layer in the device off-state.

Mode Analysis of Pt/LGS Surface Acoustic Wave Devices.

Platinum (Pt) gratings on langasite (LGS) substrates are a widely used structures in high temperature surface acoustic wave (SAW) devices. Multiple modes can be excited in PtLGS SAW devices owing to the heavy weight of the Pt electrode and leaky waves in the LGS substrate. In this work, we report on a detailed mode analysis of PtLGS SAW devices, where three commonly used LGS cuts are considered. A three-dimensional (3D) finite element method (FEM) numerical model was developed, and the simulation and experiment results were compared. The experiment and simulation results showed that there are two modes excited in the PtLGS SAW devices with Euler angle (0, 138.5, 27) and (0, 138.5, 117), which are Rayleigh-type SAW and SH-type leaky wave, respectively. Only the Rayleigh-type mode was observed in the PtLGS SAW devices with Euler angle (0, 138.5, 72). It was found that the acoustic velocities are dependent on the wavelength, which is attributed to the change of wave penetration depth in interdigital transducers (IDTs) and the velocity dispersion can be modulated by the thickness of the Pt electrode. We also demonstrated that addition of an Al2O3 passivation layer has no effect on the wave modes, but can increase the resonant frequencies. This paper provides a better understanding of the acoustic modes of PtLGS SAW devices, as well as useful guidance for device design. It is believed that the Rayleigh-type SAW and SH-type leaky waves are potentially useful for dual-mode sensing applications in harsh environments, to achieve multi-parameter monitoring or temperature-compensation on a single chip.

Impact of Passivation System on Device Performance and Proton Radiation Hardness in GaN-Based MIS-HEMTs

GaN-based metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs) are intensively investigated for high power, high frequency [1] and aerospace application [2] due to its wide bandgap, high breakdown field, and high carrier density and mobility at AlGaN/GaN interface [3]. For the demonstration of high power radio-frequency and aerospace applicable devices, the passivation layer introduced on the AlGaN barrier plays significant roles for the enhancement of the frequency characteristics [4] and proton radiation hardness [2]. From this point of view, diverse passivation materials and systems have been researched in GaN-based MIS-HEMTs [2, 5, 6]. However, the detailed impact of passivation layer on the device properties and the immunity to the proton irradiation is not clear in many cases, so far.In this work, we have prepared the SiN/Al2O3 bi-layer passivation system to study the impact of mechanical stress introduced by the passivation layer deposition on the device performance (Sample A: SiN = 20 nm, Sample B: SiN/Al2O3 = 5/15 nm, Sample C: SiN/Al2O3 = 5/35 nm). The correlation between the induced mechanical stress on the GaN channel and carrier transport properties in terms of carrier concentration and mobility at hetero-interface in GaN-based MIS-HEMTs was examined. The Al2O3 layer deposited by the atomic layer deposition (ALD) provided the tensile stress which compensated the compressive stress generated by the SiN layer deposited by the plasma enhanced chemical vapor deposition (PEDVD). When the compressive stress reduces through the deposition of Al2O3 on the SiN layer, the carrier concentration and mobility at hetero-interface were increased. With decreasing compressive stress, the piezoelectric field enlarges that enhances polarization charges [7] and carrier concentration. The carrier mobility was also improved with diminishing compressive stress since the mean free path related to the lattice scattering is decreased, enhancing transconductance as well. As a result, GaN-based MIS-HEMTs with slight tensile stress in Sample C exhibits the best device performance.The proton radiation hardness according to the passivation system was studied for various passivation systems. When we compared the device characteristics before and after the proton irradiation with the fluences of 1013 and 1014 cm-2 at an energy of 5 MeV, the device properties such as threshold voltage, drain current, and transconductance were changed. After the proton radiation, the threshold voltage was negatively shifted that is identical characteristics to the metal-oxide-semiconductor device [8], rather than GaN-based HEMTs [9] as relatively large amount of holes was trapped inside of the passivation system due to the lower hole mobility than electron. The alternation of the device characteristics depended on the passivation system. The ALD-deposited Al2O3 showed superior quality compared to the PECVD-deposited SiN that was revealed by the pulse-mode stress measurements. Therefore, the hole trap sites generated by the proton irradiation and located interior of the passivation system are less when the Al2O3 layer was employed as a passivation layer, showing smaller threshold voltage shift. Moreover, the carrier mobility deterioration caused by the Coulomb scattering between the trapped holes inside the passivation system and carriers at hetero-interface was improved with the Al2O3 passivation layer. The drain current and transconductance degradation were improved by applying Al2O3 passivation layer.Our systematic measurement results highlight that the optimized SiN/Al2O3 bi-layer passivation system is promising technique for the enhancement of the device performance and improvement of proton radiation hardness in GaN-based MIS-HEMTs.AcknowledgementThis work was supported by the National Research Council of Science & Technology (NST) grant by the Korean government (MSIP) (No. CRC-19-02-ETRI).

MEMS hydrogen gas sensor for in-situ monitoring of hydrogen gas in transformer oil

Dissolved hydrogen gas analysis (DHGA) is a key aspect that defines the operational status of a transformer and is vital to the maintenance of safety standards in the power grid. In this report, we proposed, MEMS gas sensor arrays for DHGA with a specially designed system having a Wheatstone bridge circuitry with two pairs of resistors. The optimal temperature of the sensor was controlled using a monolithically integrated in-plane microheater and a temperature sensor to monitor the temperature change in the oil and to compensate for the temperature variations in resultant hydrogen sensor signals. The fabricated sensor in a transformer oil showed excellent H2 response (ΔVout = 62μV to 10 ppm and 4.71 mV to 2000 ppm). In addition, long-term stability of sensor performance was observed, confirming that the Al2O3 passivation layer and packaging were effective to enhance the robustness of the sensor in an oil environment. A customized, compact, and portable sensor interface electronics was developed and applied to the sensor system. The results obtained with the developed sensor interface were very similar to those measured with a digital multimeter. Our results demonstrate that the developed sensor system and packaging are very promising for long term monitoring of the operational status of transformers.

Impact of Passivation System on Device Performance and Proton Radiation Hardness in GaN-Based MIS-HEMTs

The impact of the passivation system on the device performance has been studied in GaN-based MIS-HEMTs using SiN/Al2O3 bi-layered passivation. The deposition of SiN and Al2O3 passivation layer induced the compressive and tensile stress on GaN channel layer, respectively. Through the Al2O3 deposition on top of SiN layer, the mechanical stress and device characteristics were modulated. The device properties such as carrier mobility and concentration at the hetero-interface were ameliorated when the slight tensile stress was applied on the GaN channel compared to the compressive stress. The proton radiation hardness corresponding to the passivation system was also researched. The SiN/Al2O3 passivation system exhibited stronger immunity to the proton radiation than that of SiN passivation due to the superior dielectric quality of Al2O3. These results highlight that the SiN/Al2O3 bi-layered passivation is promising technique for the optimization of the device performance and improvement of proton radiation hardness in GaN-based MIS-HEMTs.

Surface Passivation of InGaAs/InP p-i-n Photodiodes Using Epitaxial Regrowth of InP

The use of epitaxial regrowth of InP on lattice-matched In0.53Ga0.47 As for passivation of photodiodes lateral mesa surfaces is investigated. The effect of the regrown layer was examined by photoluminescence and dark current measurements and compared with results obtained with SiO2 and Al2O3 passivation layers. The integrated intensity of steady-state photoluminescence of InGaAs covered by InP increased by a factor between 15.5 and 58.9, depending on the excitation wavelength, denoting a strong reduction of nonradiative recombination. This reduction is expected to be the result of a strong reduction of intragap surface states. For the same photoluminescence measurements, both SiO2 and Al2O3 oxide passivation instead showed a reduction of the photoluminescence intensity. The dark currents of p-i-n photodiodes showed less striking results, a fact that we claim, probably is related to residual doping of the InP regrown layer.

Simultaneously Defined Semiconducting Channel Layer Using Electrohydrodynamic Jet Printing of a Passivation Layer for Oxide Thin-Film Transistors.

A simple fabrication method for homojunction-structured Al-doped indium-tin oxide (ITO) thin-film transistors (TFTs) using an electrohydrodynamic (EHD) jet-printed Al2O3 passivation layer with specific line (WAl2O3) is proposed. After EHD jet printing, the specific region of the ITO film below the Al2O3 passivation layer changes from a conducting electrode to a semiconducting channel layer simultaneously upon the formation of the passivation layer during thermal annealing. The channel length of the fabricated TFTs is defined by WAl2O3, which can be easily changed with varying EHD jet printing conditions, i.e., no need of replacing the mask for varying patterns. Accordingly, the drain current and resistance of the fabricated TFTs can be modified by varying the WAl2O3. Using the proposed method, a transparent n-type metal-oxide-semiconductor (NMOS) inverter with an enhancement load can be fabricated; the effective resistance of load and drive TFTs is easily tuned by varying the processing conditions using this simple method. The fabricated NMOS inverter exhibits an output voltage gain of 7.13 with a supply voltage of 10 V. Thus, the proposed approach is promising as a low-cost and flexible manufacturing system for multi-item small-lot-sized production of Internet of Things devices.

145-MW/cm2 Heteroepitaxial Diamond MOSFETs With NO2 p-Type Doping and an Al2O3 Passivation Layer

In this study, we investigated diamond metal oxide semiconductor field effect transistors (MOSFETs) with NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> p-type doping and Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> passivation layer fabricated on a high-quality heteroepitaxial single crystal (001) diamond substrate called Kenzan diamond <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">®</sup> . MOSFETs with a gate length of 1.4 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> and nearly zero source-gate spacing exhibited a high drain current density of −776 mA/mm with a negligible gate leakage current ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&lt; 0.1~\mu \text{A}$ </tex-math></inline-formula> /mm). MOSFETs with a gate-to-drain length of 4.8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> delivered a high off-state breakdown voltage (−618 V) at an average breakdown field of 1.2 MV/cm and a specific on-resistance of 2.63 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}\Omega \cdot $ </tex-math></inline-formula> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Baliga’s Figure-Of-Merits was calculated as 145 MW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and the anticipated maximum power density was 12 W/mm. The diamond MOSFET was improved with high crystal quality.

Impact of HfO₂ as a Passivation Layer in the Solar Cell Efficiency Enhancement in Passivated Emitter Rear Cell Type.

We report the simulation of high-efficiency c-silicon Passivated Emitter Rear Contact (PERC) type solar cell structure with rear side passivated with HfO₂ as a passivating material. Variation in the half length of pyramid has been carried out to investigate its effect on the solar cell electrical characteristics such as fill factor (FF), open circuit voltage (Voc) and efficiency. Aluminum back Surface Field (Al-BSF) and PERC type solar cell with Al₂O₃ passivation layer structures were also modeled for comparison. Effect of variation in passivation layer (HfO₂) thickness (10 and 15 nm) and permittivity (k = 14 and 25) on the solar cell electrical characteristics has been investigated. Result shows the efficiency improvement in the PERC solar cell with HfO₂ passivation layer by 0.5941% and 0.983% as compared to the Al-BSF and PERC with Al₂O₃ passivation layer at 8 μm pyramid half length. Increased series resistance and reduced FF has been observed with the incorporation of passivation layer at the solar cell structure. Negligible effect of passivation layer thickness has been observed on the solar cell electrical parameters whereas the permittivity value does have significant effect.

Decorating non-noble metal plasmonic Al on a TiO2/Cu2O photoanode to boost performance in photoelectrochemical water splitting

Designing low-cost and high-performance photoelectrodes with improved light harvesting and charge separation rates is significant in photoelectrochemical water splitting. Here, a novel TiO2/Cu2O/Al/Al2O3 photoelectrode is manufactured by depositing plasmonic nanoparticles of the non-noble metal Al on the surface of a TiO2/Cu2O core/shell heterojunction for the first time. The Al nanoparticles, which exhibit a surface plasmon resonance (SPR) effect and are substantially less expensive than noble metals such as Au and Ag, generate hot electron–hole pairs and amplify the electromagnetic field at the interface under illumination. The as-prepared TiO2/Cu2O/Al/Al2O3 photoelectrodes have an extended absorption range and enhanced carrier separation and transfer. Their photocurrent density of 4.52 mA·cm−2 at 1.23 V vs. RHE represents an 1.84-fold improvement over that of TiO2/Cu2O. Specifically, the ultrathin Al2O3 passivation layer spontaneously generated on the surface of Al in air could act as a protective layer to significantly increase its stability. In this work, the synergistic effect of the heterojunctions and the SPR effect of the non-noble metal Al significantly improve the photoelectrode performance, providing a novel concept for the design of electrodes with good properties and high practicability.

Atomic layer deposition of Al2O3 on LiNi0.68Co0.10Mn0.22O2 for enhanced electrochemical performance

Although there have been many studies on atomic layer deposition of Al2O3 to improve the electrochemical performances of ternary cathode materials, few studies considered the harsh conditions such as high temperature and high voltage at the same time. In this work, the Al2O3 passivation layer is employed to coat the high nickel (Ni) LiNi0.68Co0.10Mn0.22O2 cathode through atomic layer deposition (ALD) approach. The Al2O3 coated LiNi0.68Co0.10Mn0.22O2 presents superior cycling stability and rate capability than the pristine at the cut-off voltage of 2.7–4.4 V under room temperature. Furthermore, under the harsh condition at high temperature of 60 °C or at high voltage of 2.7–4.8 V, the Al2O3 coated LiNi0.68Co0.10Mn0.22O2 also shows significantly improved performances than the pristine. The superior electrochemical performance of Al2O3 coated LiNi0.68Co0.10Mn0.22O2 could be attributed to the enhanced interfacial stability, the mitigated side reactions with electrolyte and the better maintained lithium ion diffusion kinetics. Manipulating the surface coating chemistry and evaluating the performance under harsh condition provide a useful approach for fast screening of effective surface modification technology, which might significantly advance the development of high energy density cathode materials.