Dielectric Passivation Research Articles

Substantial improvement of InGaN/GaN visible-light polarization-induced self-depletion phototransistor by thermally oxidized Al2O3

Atomic layer deposited (ALD) Al2O3 acting as gate dielectric and surface passivation is widely adopted in power electronics but seldom used in optoelectronic fields for its sophisticated and expensive technology. Herein, a simple but efficient Al2O3 passivation is used in the fabrication of InGaN/GaN visible-light (VL) polarization-induced self-depletion field effect phototransistors (FEPTs), for suppressing the surface leakage and recombination. The Al2O3 layer obtained by thermal oxidation (TO) of 2-nm-thick thermally evaporated metal Al shows high electrical insulation and even better passivation effect than the ALD-Al2O3. As a result, the dark current of TO-Al2O3 passivated device decreases by about 2 orders of magnitudes; meanwhile, the photoresponse increases by about 65%. Under a weak VL illumination of 6.8 μW/cm2, the InGaN/GaN FEPT exhibits a large photo-to-dark current ratio of 3.1 × 108 and an ultrahigh shot-noise-limited detectivity of 1.9 × 1018 jones. In addition, the FEPTs exhibit a strong wavelength selectivity with a 600 nm/400 nm spectral response rejection ratio exceeding 5 × 105. All these performances show huge potential in emerging VL applications that are limited by the insufficiencies of current Si photodetectors.

Dielectric screening modulating charge carrier recombination in high-performance of CsPbI2Br carbon-based perovskite solar cells

As a type of ionic crystal, CsPbI2Br perovskite inevitably generates a significant number of defects during the rapid crystallization process that occurs from deposition to annealing. The non-radiative recombination of charge carriers caused by these defects severely limits the performance of perovskite solar cells (PSCs). Here, 2,2,2-trifluoroethylamine hydrochloride (F3EACl) with permanent dipole moment is devised to modify the perovskite interface. Highly electronegative trifluoro groups can accelerate the dielectric response of perovskite films, intensify the dielectric screening effect, and significantly suppress non-radiative recombination of charge carriers. Meanwhile, the –NH3+ group in F3EACl effectively passivates the defects at the perovskite surface, further alleviating the defect-induced carrier recombination loss. Consequently, the CsPbI2Br carbon-based PSCs treated with F3EACl achieved an impressive power conversion efficiency (PCE) of 14.69 % at a higher open-circuit voltage (1.28 V), along with excellent environmental stability. This work demonstrates a unique tactic to achieve efficient and stable PSCs by modulating charge carrier recombination utilizing the synergistic effects of dielectric screening and defect passivation.

Operational Characteristics of AlGaN/GaN High-Electron-Mobility Transistors with Various Dielectric Passivation Structures for High-Power and High-Frequency Operations: A Simulation Study.

This study investigates the operational characteristics of AlGaN/GaN high-electron-mobility transistors (HEMTs) by employing various passivation materials with different dielectric constants and passivation structures. To ensure the simulation reliability, the parameters were calibrated based on the measured data from the fabricated basic Si3N4 passivation structure of the HEMT. The Si3N4 passivation material was replaced with high-k materials, such as Al2O3 and HfO2, to improve the breakdown voltage. The Al2O3 and HfO2 passivation structures achieved breakdown voltage improvements of 6.62% and 17.45%, respectively, compared to the basic Si3N4 passivation structure. However, the increased parasitic capacitances reduced the cut-off frequency. To mitigate this reduction, the operational characteristics of hybrid and partial passivation structures were analyzed. Compared with the HfO2 passivation structure, the HfO2 partial passivation structure exhibited a 7.6% reduction in breakdown voltage but a substantial 82.76% increase in cut-off frequency. In addition, the HfO2 partial passivation structure exhibited the highest Johnson's figure of merit. Consequently, considering the trade-off relationship between breakdown voltage and frequency characteristics, the HfO2 partial passivation structure emerged as a promising candidate for high-power and high-frequency AlGaN/GaN HEMT applications.

Strain‐Engineered Unified SiNx Deposition for Device Passivation and Capacitance Dielectric in GaN Monolithic Microwave Integrated Circuit

Silicon nitride (SiNx) is used for device passivation and capacitance dielectric in GaN monolithic microwave integrated circuits. However, this is a conflicting requirement as passivation requires SiNx to cause tensile strain, and capacitance dielectric primarily demands a high breakdown voltage and large dielectric constant for SiNx, leading to a damaged AlGaN surface during deposition. Two independent SiNx depositions under two different conditions (silicon‐ and nitrogen‐rich) are usually carried out to meet both requirements. Herein, a solution for a unified deposition through interfacial strain analysis on an AlGaN/GaN heterostructure grown on 6H‐SiC imposed by thin film silicon nitride (SiNx), deposited using inductively coupled plasma chemical vapor deposition system is proposed. The strain analysis is done using Raman spectroscopy. The surface morphology of the SiNx is studied using atomic force microscopy. The breakdown characteristics are ascertained from measurements on high electron mobility transistors and metal–insulator–metal capacitors.

Battery pack passive insulation strategies of electric vehicles under a frigid environment

Further application of electric vehicles (EVs) in frigid regions is hindered by the diminished performance of lithium-ion batteries (LIBs) at sub-zero temperatures. Developing efficient heat preservation strategies has significant implications for the broad application of EVs and LIBs. This study focuses on passive heat preservation strategies (PHPS) for battery packs in frigid environments (−30 °C). A validated 3D battery pack heat preservation model integrated with airflow is constructed in this paper, and the model analysis results indicate that arranging aerogels at the pack level provides superior heat preservation compared to cell and module levels. Additionally, the influence of flow field distribution (FFD) schemes on heat preservation performance is discovered. Both experimental and simulation results confirm that the proposed scheme can optimize the cooling rate to about 2.3 °C/h. Commencing from an initial temperature of 30 °C, extending the battery pack retention time above 0 °C to over 12 h under −30 °C can significantly expand the application of electric vehicles in frigid regions. This paper explores the primary factors affecting the heat dissipation of battery packs in the frigid temperature environment, which have great significance in guiding the heat preservation design of battery systems.

Numerical simulation of insulated drilling technique with refrigerant fluid in the Arctic region

In recent years, there has been a gradual rise in the exploitation of the abundant oil and gas resources in the Arctic. Drilling operations in the permafrost regions of the Arctic can induce thermal energy transfer from the drilling fluid to the permafrost layer, causing permafrost thawing and potentially leading to wellbore instability. Especially when the reservoirs are in deeper formations, the challenge intensifies. In response, some researchers suggest a new drilling technique which adopts the method of injecting refrigerant fluid and vacuum insulated tubing (VIT) cementing for active and passive insulation, respectively. However, due to the novelty of this technique and the complex hydrothermal process in permafrost layers, current studies and numerical models struggle to accurately assess the insulation effect of this method during practical drilling operations. Therefore, referring to previous related research, this article establishes a coupled thermal modeling of this drilling method based on the hydrothermal theory of permafrost. The thermal insulation effect, as well as characteristics of wellbore and formation of this drilling method was investigated through numerical simulation. The findings reveal that compared to conventional drilling methods, this method can effectively delay heat transfer from the wellbore to the permafrost and ensure the volume of thawed permafrost less than 100 m3. Lastly, it is recommended to choose VIT with a thermal conductivity coefficient of less than 0.04 W/(m∙℃), or ensure a flow rate of refrigerant fluid above 7.5 L/s and an injection temperature of refrigerant fluid less than −5 °C when the thermal conductivity of VIT is above 0.04 W/(m∙℃). The model and calculations provided in this paper offer some insights for the implementation of this innovative insulated drilling technique in the Arctic region.

Development and performance evaluation of active insulation systems using solid-state thermal switches

Traditional building envelopes have passive insulation systems that cannot respond to dynamic changes in the environment. An Active Insulation System (AIS) consists of Active Insulation Materials (AIMs) that dynamically vary the thermal conductivity of the insulation system. Several researchers have evaluated the impact of AIS on building thermal and energy performance by using simulation tools. Up to 70% savings in annual heating and cooling energy and significant reductions in peak demand have been predicted for some climates with wall systems employing AIS. However, materials and assembly development still need a cost-effective product that achieves the required performance. In this study, we present the process of developing an AIS that we will install in a test hut for its performance evaluation. Minimum performance criteria of the AIS system are developed based on R-low/R-high ratio, required time and efficiency to switch states, and cost estimates. The following steps during this study are creating the concept to meet the requirements, predicting the performance via simulations, developing the experimental setup for bench-scale testing, and finally, constructing a full-scale wall assembly and monitoring the performance when exposed to environmental chamber tests. The selected approach uses off-the-shelf products to create an AIS that can switch R-value between 0.98 ft2·°F·h/BTU (0.173 m2·K/W) and 5.81 ft2·°F·h/BTU (1.02 m2·K/W) and have a switching time of less than one minute between R-high and R-low.

Etching-free pixel definition in InGaN green micro-LEDs

The traditional plasma etching process for defining micro-LED pixels could lead to significant sidewall damage. Defects near sidewall regions act as non-radiative recombination centers and paths for current leakage, significantly deteriorating device performance. In this study, we demonstrated a novel selective thermal oxidation (STO) method that allowed pixel definition without undergoing plasma damage and subsequent dielectric passivation. Thermal annealing in ambient air oxidized and reshaped the LED structure, such as p-layers and InGaN/GaN multiple quantum wells. Simultaneously, the pixel areas beneath the pre-deposited SiO2 layer were selectively and effectively protected. It was demonstrated that prolonged thermal annealing time enhanced the insulating properties of the oxide, significantly reducing LED leakage current. Furthermore, applying a thicker SiO2 protective layer minimized device resistance and boosted device efficiency effectively. Utilizing the STO method, InGaN green micro-LED arrays with 50-, 30-, and 10-µm pixel sizes were manufactured and characterized. The results indicated that after 4 h of air annealing and with a 3.5-μm SiO2 protective layer, the 10-µm pixel array exhibited leakage currents density 1.2 × 10−6 A/cm2 at −10 V voltage and a peak on-wafer external quantum efficiency of ~6.48%. This work suggests that the STO method could become an effective approach for future micro-LED manufacturing to mitigate adverse LED efficiency size effects due to the plasma etching and improve device efficiency. Micro-LEDs fabricated through the STO method can be applied to micro-displays, visible light communication, and optical interconnect-based memories. Almost planar pixel geometry will provide more possibilities for the monolithic integration of driving circuits with micro-LEDs. Moreover, the STO method is not limited to micro-LED fabrication and can be extended to design other III-nitride devices, such as photodetectors, laser diodes, high-electron-mobility transistors, and Schottky barrier diodes.

Thermal performance of a wooden pipe-embedded building envelope using a low-grade heat source in extreme cold climate conditions

A pipe-embedded wall can effectively reduce building energy consumption in winter. Most of the research on this concept to date has used traditional building materials such as concrete and brick. This paper reports on a wooden pipe-embedded wall allowing more flexible pipe locations, which can be used to reduce heat load in winter. An experimental assessment was developed to investigate the building assemblies thermal performance and the results were used to develop an understanding of its thermal energy saving potential, and as an input for the validation of a numerical model of same. A 3D computational fluid dynamics model of the pipe-embedded wall was developed and applied to assess the thermal performance of the wall under boundary conditions beyond the capabilities of the experimental assessment. Further, the influence of five parameters including the outdoor temperature and pipe positions were studied. A method was proposed for selecting the pipe layer's optimal location. The results show dual thermal impacts of the pipe layer: active heating and passive insulation. Using 8 °C water reduces internal surface heat transfer by 42.5 % under −20 °C outdoor temperature conditions. This is akin to an 18 °C outdoor temperature rise. Furthermore, another interesting result is that increasing the wall material thermal resistance can sometimes increase energy consumption. This study provides a reference for designing and optimizing net zero energy buildings in extreme cold climate conditions.

Application of Modified Passive Insulation Monitors for Selective Earth Fault Location in Live Low Voltage AC IT Circuits

In the publication there are presented most popular passive methods of continuous insulation monitoring in live low voltage unearthed AC networks. There are given formulas for determination of insulation equivalent resistance for multi-phase networks sources with both symmetrical and asymmetrical voltages. Novel solution of elimination of the most popular measuring scheme’s shortcomings is proposed. New methods of insulation resistance measurement and earth fault location based on supervision

CIGS bifacial solar cells with novel rear architectures: Simulation point of view and the creation of a digital twin

The performance of bifacial Cu(In,Ga)Se2 (CIGS) cells does not yet reach the one of monofacial cells, with standard Mo rear contacts. By exploring optoelectronic simulations, this study addresses the impact of a transparent conducting oxide layer used as rear contact in CIGS solar cells. These simulations, which aim to create a digital twin of bifacial CIGS solar cells, offer insight into the impact of novel rear contact architectures. It was observed that with an indium tin oxide (ITO) rear contact the CIGS cell performance lacks in comparison to a Mo one due to an electrical barrier, under rear side illumination these devices may only reach 3.9 % in conversion efficiency. The implementation of dielectric rear passivation schemes have great performance benefits in cells with Mo rear contacts. Therefore, the same passivation strategy in ITO contacts is discussed and additional novel architectures are proposed, from which a design of alternated lines between dielectric and 15 nm Mo layers on ITO showed promising results. Such rear architectures aim to achieve i) a highly transparent rear contact, ii) an ohmic-like behaviour with CIGS, and iii) a low defective interface with rear passivation. The selenization of the complete 15 nm Mo in the proposed novel architecture during the CIGS growth was considered, resulting in transmittance values above 70 % and, notably, reaching the transparency of bare ITO in the infrared range. Such rear architecture may provide for bifacial CIGS solar cells with conversion efficiency values surpassing 20 and 15 % for front and rear side illumination, respectively, allowing to fully exploit bifaciality.

Investigating the impact of edge passivation on shingle solar modules

This work deals with solar modules made from rectangular-shaped solar cell strips, so-called shingles, that are interconnected by overlapping one with another. For the fabrication of such modules, host solar cells are cut into several shingles resulting in unpassivated shingle cell edges and relevant recombination losses. As discussed in this work based on simulations, quantifying these losses on module level is not straightforward and is ideally done by referring to the pseudo fill factor pFF. In this context, it is shown that by passivating the cut edges of the shingles by depositing a dielectric layer, a significant pFF increase can be achieved both on shingle as well as on module level. Considering the highest respective pFF value found for modules with and without edge passivation, an increase of ΔpFF = 0.5%abs is reached. At the same time, no significant compromise of the interconnection quality is observed. These results are obtained for monofacial passivated emitter and rear cell (PERC) shingles. In short, this work is the first comprehensive analysis of experimental data on module level in the context of edge passivation. It demonstrates that the deposition of a dielectric passivation layer at the shingle's edges can boost pFF of shingle solar modules, while the current transit between the busbars of jointed shingles is not significantly hindered.

Development of a Plasmonic Light Management Architecture Integrated within an Interface Passivation Scheme for Ultrathin Solar Cells

In response to climate and resource challenges, the transition to a renewable and decentralized energy system is imperative. Ultrathin Cu(In,Ga)Se2 (CIGS)‐based solar cells are compatible with such transition due to their low material usage and improved production throughput. Despite the benchmark efficiency of CIGS technology, ultrathin configurations face efficiency drops arising from increased rear interface recombination and incomplete light absorption. Dielectric passivation schemes address rear interface recombination, but achieving simultaneous electrical and optical gains is crucial for thinning down the absorber. Plasmonic nanoparticles emerge as a solution, enhancing light interaction through resonant scattering. In the proposed architecture, the nanoparticles are encapsulated within a dielectric rear passivation layer, combining effective passivation and light trapping. A controlled deposition and encapsulation of individualized nanoparticles is achieved by an optimized process flow using microfluidic devices and nanoimprint lithography. With the developed plasmonic and passivated architecture, a 3.7 mA cm−2 short‐circuit current density and a 23 mV open‐circuit voltage improvements are obtained, leading to an almost 2% increase in light‐to‐power conversion efficiency compared to a reference device. This work showcases the developed architecture potential to tackle the electrical and optical downfalls arising from the absorber thickness reduction, contributing to the dissemination of ultrathin technology.

Analysis of breakdown voltage for GaN MIS-HEMT with various composite field plate configurations and passivation layers

The effects of different field plate designs on the breakdown voltage of GaN Metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs) were examined in this study. The study's primary goal was to determine the dependence of breakdown voltage with respective to composite field plate designs using TCAD simulation. For devices featuring only G-FP, with a fixed gate to drain distance of 15 μm and a fixed G-FP to drain distance of 15 μm, the maximum breakdown voltage was achieved 1 μm G-FP. Breakdown voltage trends were also determined for composite field plate configurations, such as adding a source field plate (S-FP) or a drain field plate (D-FP) with a fixed 1 μm G-FP length. A further enhancement in device breakdown performance was demonstrated by employing a novel D-FP structure. A single D-FP improves the breakdown voltage from 1.4 kV (conventional breakdown voltage with 1um G-FP) to 1.6 kV when combined with 1 μm G-FP, while the novel two-step D-FP achieves a breakdown voltage of about 1.7 kV when combined with 1 μm G-FP. We also investigated the influence of high-k dielectric passivation layers on the breakdown voltage. The breakdown voltage of the devices with optimized G-FP can be further improved by using high-k dielectric material as a passivation layer. The thorough investigations contribute to a better understanding of GaN MIS-HEMT breakdown characteristics and prospective pathways for improving their performance via unique field plate designs and superior dielectric materials.

Optical analysis of III-nitride micro-light-emitting diodes with different sidewall treatments at low current density operation

In this work, the optical efficiency of III-nitride blue micro-LEDs (μLEDs) ranged from 5 × 5 to 60 × 60 μm2 with different sidewall treatments at low current density range was investigated. The results showed dielectric sidewall passivation using atomic layer deposition (ALD) has superior optical enhancement compared to conventional RF sputtering, where most of the enhancement occurred at low current density range. Additionally, the use of ALD sidewall passivation and chemical treatment offered significant efficiency improvement for different sizes of μLEDs at operating less than 1 A cm−2 and the devices without sidewall treatments did not emit light. The effect of sidewall treatments to the effective Shockley–Read–Hall (SRH) nonradiative recombination coefficient, or the effective A coefficient from the ABC model, was estimated. The effective SRH nonradiative recombination coefficient was suppressed by two orders of magnitude for devices with sidewall treatments compared to devices without sidewall passivation.

Enhancing dielectric passivation on monolayer WS2 via a sacrificial graphene oxide seeding layer

The full utilization of two-dimensional transition metal dichalcogenides (2D TMDCs) faces several challenges, among which is realizing uniform material deposition on the 2D surface. Typical strategies to enable material growth lead to a poor interface quality, degrading the 2D TMDC’s properties. In this work, a sacrificial, graphene oxide-based seeding layer is used (1) as passivation layer, protecting the underlying 2D TMDC and (2) as nucleation layer, enabling uniform material growth. Graphene is transferred on monolayer WS2, establishing a high-quality van der Waals interface. After transfer, the polymeric residues on graphene are cleaned via a combination of wet- and dry treatments and functionalized via dry UV/O3 oxidation. The rate of graphene oxidation is shown to be substrate dependent, which is explained by UV light-induced ultrafast charge transfer between the graphene and WS2 monolayer. The carbon-oxygen functionalities serve as nucleation sites in a subsequent HfO2 ALD process, achieving more uniform dielectric growth and faster layer closure compared to direct deposition. The graphene-based nucleation- / passivation approach offers adaptability, allowing for tailored surface chemistry to enable any alternative material growth, while maintaining a prefect van der Waals interface.

Enhanced robustness against hot-electron-induced degradation in active-passivation p-GaN gate HEMT

The hot-electron-related reliability is an important issue for GaN power devices under harsh operation condition or environment. These high-energy electrons can scatter toward the device surface or buffer layer, introducing newly generated traps/defects and resulting in the degradation of dynamic ON-resistance (RON). This work investigates the dynamic characteristics in active-passivation p-GaN gate HEMTs (AP-HEMTs) after hot-electron stress (HES). Unlike the dielectric passivation whose dynamic RON performance is often reported to severely worsen as hot-electron-induced defects/traps accumulate, the active passivation is found to have a superior robustness against hot-electron stress. In this study, after an HES of 30 min with VD = 200 V and IS = 10 mA/mm, the dynamic RON/static RON of a conventional HEMT increases dramatically from 3.63 to 9.35 for VDS-OFF = 650 V, whereas that of AP-HEMT only shows a slight increase from 1.51 to 1.85. Two mechanisms have been experimentally proved for the improved hot-electron robustness in AP-HEMT. (i) The mobile holes in active passivation layer can effectively screen the preexisting and/or newly generated surface defects/traps from affecting the 2DEG channel. (ii) The recovery of buffer trapping is accelerated by hole injection from gate and active passivation.

Improving AlGaInP Micro-LEDs Characteristics via Varied Dielectric Passivation Layers

Improving AlGaInP Micro-LEDs Characteristics via Varied Dielectric Passivation Layers

Stable and low loss oxide layer on α-Ta (110) film for superconducting qubits

The presence of amorphous oxide layers can significantly affect the coherent time of superconducting qubits due to their high dielectric loss. Typically, the surface oxides of superconductor films exhibit lossy and unstable behavior when exposed to air. To increase the coherence time, it is essential for qubits to have stable and low dielectric loss oxides, either as barrier or passivation layers. In this study, we highlight the robust and stable nature of an amorphous tantalum oxide layer formed on α-Ta (110) film by employing chemical and structural analyses. Such kind of oxide layer forms in a self-limiting process on the surface of α-Ta (110) film in piranha solution, yielding stable thickness and steady chemical composition. Quarter-wavelength coplanar waveguide resonators are made to study the loss of this oxide. One resonator has a Qi of 3.0 × 106 in the single photon region. The Qi of most devices are higher than 2.0 × 106. Moreover, most of them are still over 1 × 106 even after exposed to air for months. Based on these findings, we propose an all-tantalum superconducting qubit utilizing such oxide as passivation layers, which possess low dielectric loss and improved stability.

Stability of Near-Surface Nitrogen Vacancy Centers Using Dielectric Surface Passivation.

We study the photophysical stability of ensemble near-surface nitrogen vacancy (NV) centers in diamond under vacuum and air. The optically detected magnetic resonance contrast of the NV centers was measured following exposure to laser illumination, showing opposing trends in air compared to vacuum (increasing by up to 9% and dropping by up to 25%, respectively). Characterization using X-ray photoelectron spectroscopy (XPS) suggests a surface reconstruction: In air, atmospheric oxygen adsorption on a surface leads to an increase in NV- fraction, whereas in vacuum, net oxygen desorption increases the NV0 fraction. NV charge state switching is confirmed by photoluminescence spectroscopy. Deposition of ∼2 nm alumina (Al2O3) over the diamond surface was shown to stabilize the NV charge state under illumination in either environment, attributed to a more stable surface electronegativity. The use of an alumina coating on diamond is therefore a promising approach to improve the resilience of NV sensors.