Al2O3 Passivation Layer Research Articles

Hydrogen-terminated polycrystalline diamond MOSFETs with Al2O3 passivation layers grown by atomic layer deposition at different temperatures

Metal oxide semiconductor field effect transistors (MOSFETs) with Al2O3 passivation layer grown by atomic layer deposition (ALD) at 200 oC and 300 oC were fabricated on hydrogen-terminated polycrystalline diamond by using gold mask technology. The device with 200 oC grown Al2O3 dielectric shows high output current, low on-resistance, large threshold voltage and high transconductance compared to that with 300 oC grown Al2O3. A maximum drain current of 339 mA/mm has been achieved by the 2-μm device of the former kind, which, as we know, is the best result reported for the diamond MOSFETs with the same gate length except the NO2-adsorbed case. The current-voltage (I-V) of gate diodes of both kinds of devices show the gate forward leakage is dominated by the Frenkel-Poole (FP) emission mechanism at a high electric field, and the gate of the latter device can sustain higher forward bias. The stability of successive I-V measurements of both kinds of devices was proved. We expect that a high performance H-diamond MOSFET with high stability can be achieved by a double-layer dielectric structure with 200 oC grown Al2O3 stacked by another high-quality high κ dielectric.

Improving the Explosive Performance of Aluminum Nanoparticles with Aluminum Iodate Hexahydrate (AIH)

A new synthesis approach for aluminum particles enables an aluminum core to be passivated by an oxidizing salt: aluminum iodate hexahydrate (AIH). Transmission electron microscopy (TEM) images show that AIH replaces the Al2O3 passivation layer on Al particles that limits Al oxidation. The new core-shell particle reactivity was characterized using laser-induced air shock from energetic materials (LASEM) and results for two different Al-AIH core-shell samples that vary in the AIH concentration demonstrate their potential use for explosive enhancement on both fast (detonation velocity) and slow (blast effects) timescales. Estimates of the detonation velocity for TNT-AIH composites suggest an enhancement of up to 30% may be achievable over pure TNT detonation velocities. Replacement of Al2O3 with AIH allows Al to react on similar timescales as detonation waves. The AIH mixtures tested here have relatively low concentrations of AIH (15 wt. % and 6 wt. %) compared to previously reported samples (57.8 wt. %) and still increase TNT performance by up to 30%. Further optimization of AIH synthesis could result in additional increases in explosive performance.

Highly pure yellow light emission of perovskite CsPb(BrxI1-x)3 quantum dots and their application for yellow light-emitting diodes

High-quality all-inorganic perovskite CsPb(BrxI1-x)3 quantum dots (QDs) with quantum yield of 50% were systematically studied as yellow light convertor for light emitting diodes (LEDs). A novel heat insulation structure was designed for the QD-converted yellow LEDs. In this structure, a silicone layer was set on top of the GaN LED chip to prevent directly heating of the QDs by the LED chip. Then the CsPb(BrxI1-x)3 QDs were filled in the bowl-shaped silicone layer after ultrasonic dispersion treatment. Finally, an Al2O3 passivation layer was grown on the QDs layer by Atomic Layer Disposition at 40 °C. When x = 0.55, highly pure yellow LEDs with an emission peak at ∼570 nm and a full width at half maximum of 25 nm were achieved. The chromaticity coordinates of the QD-converted yellow LEDs (0.4920 ± 0.0017, 0.4988 ± 0.0053) showed almost no variation under driving current from 5 mA to 150 mA. During an operation period of 60 min, the emission wavelength of the yellow LEDs showed no distinct shift. Moreover, the luminous efficiency of the QD-converted yellow LEDs achieved 13.51 l m/W at 6 mA. These results demonstrated that CsPb(BrxI1-x)3 QDs and the heat insulation structure are promising candidate for high purity yellow LEDs.

Interface Modulation and Optimization of Electrical Properties of HfGdO/GaAs Gate Stacks by ALD‐Derived Al2O3 Passivation Layer and Forming Gas Annealing

AbstractMetal‐oxide‐semiconductor (MOS) capacitors with sputtering‐deposited Gd‐doped HfO2(HGO) high k gate dielectric thin films and ALD‐derived Al2O3 interfacial passivation layer were fabricated on GaAs substrates. The effects of the passivation layer and the forming gas annealing (FGA) temperature were explored by studying the interfacial chemical bonding states and electrical properties of HGO/GaAs and HGO/Al2O3/GaAs gate stacks via x‐ray photoelectron spectroscopy (XPS), capacitance‐voltage (C–V), and leakage current density‐voltage ( J–V) measurements. Results indicated that the MOS capacitors performances were enhanced by performing FGA. The electrical analysis revealed that the 300 °C‐annealed Al/HGO/GaAs/Al MOS capacitor with 20 cycles Al2O3 passivation layer experienced improved electrical properties, with a dielectric constant of 44, a flat band voltage of 0.64 V, a hysteresis of 0.02 V corresponding to the oxide charge density of −6.2 × 1012 cm2, border trapped oxide charge density of −3.02 × 1011 cm2, a leakage current density 5.87 × 10‐6 A/cm2 at a bias voltage of 2 V. The low temperature (77–300 K) dependent detailed current conduction mechanisms (CCMs) of the 300 °C‐annealed MOS capacitor at low temperatures were also systematically investigated. The optimized interface chemistry and the excellent electrical properties suggested that HGO/Al2O3/GaAs potential gate stacks could be applied in future III‐V‐based MOSFET devices.

Facile Room Temperature Routes to Improve Performance of IGZO Thin-Film Transistors by an Ultrathin Al2O3Passivation Layer

Although oxide thin-film transistors (TFTs) have drawn great interests in flexible displays, a key obstacle is the requirement of high-temperature annealing to realized mobility>10 cm $^{2}/\text {V}\cdot \text {s}$ . In this paper, a fully room-temperature strategy, involving the deposition of ~10 nm In–Ga–Zn–O (IGZO) channel layer and ~4 nm Al2O3 passivation layer, is introduced. The as-prepared flexible TFT on polymide substrate exhibits a saturation mobility of 15.3 cm $^{2}/\text {V}\cdot \text {s}$ , $V_{{\text {th}}}$ of 3.08 V, and on/off current ratio of $2.3\times 10^{{\text {7}}}$ . Thickness-dependent analysis indicates that the interface between Al2O3 and IGZO is composed of negative O-rich layer, which impel the energy band bending inside the IGZO layers and release of electrons from traps. This paper opens up a route to achieve fully room-temperature fabrication of high-performance flexible TFT.

High-pressure oxygen annealing of Al2O3 passivation layer for performance enhancement of graphene field-effect transistors

High-pressure annealing in oxygen ambient at low temperatures (∼300 °C) was effective in improving the performance of graphene field-effect transistors. The field-effect mobility was improved by 45% and 83% for holes and electrons, respectively. The improvement in the quality of Al2O3 and the reduction in oxygen-related charge generation at the Al2O3-graphene interface, are suggested as the reasons for this improvement. This process can be useful for the commercial implementation of graphene-based electronic devices.

Effects of Backchannel Passivation on Electrical Behavior of Hetero-Stacked a-IWO/IGZO Thin Film Transistors

This study investigates the effects of positive gate-bias stress (PGBS) on the electrical instability of amorphous InWO/InGaZnO (a-IWO/IGZO) stacked thin-film transistors (TFTs) with a backchannel passivation layer of SiO2 or Al2O3 film. After the application of PGBS to a-IWO/IGZO TFTs with an SiO2 passivation layer, abnormal negative threshold voltage (Vth) shifts were observed, while positive Vth shifts were observed in the TFTs with an Al2O3 passivation layer. This unusual positive bias instability is explained using a two-step electrical degradation behavior model, including both electron trapping and moisture absorption at the damaged back channel interface between a-IWO/IGZO TFTs and the SiO2 passivation layer.

Enhanced Carrier Transport Properties in GaN-Based Metal-Insulator-Semiconductor High Electron Mobility Transistor with SiN/Al2O3 Bi-Layer Passivation

The impacts of SiN/Al2O3 bi-layer passivation on the carrier transport characteristics in GaN-based metal-insulator-semiconductor high electron mobility transistors (MISHEMTs) were studied. Various mechanical stresses, as measured by micro-Ramam spectroscopy, were introduced on the GaN channel according to the different passivation systems. The SiN dielectric layer deposited by plasma enhanced chemical vapor deposition on top of the GaN capping layer resulted in compressive stress. On the other hand, the Al2O3 passivation layer deposited by atomic layer deposition on SiN layer generated tensile stress, which compensated the compressive stress produced by the SiN layer. The correlation between the applied mechanical stress induced by the deposited dielectric layers and device performance of the GaN-based HEMT was also investigated. When a slight tensile stress was applied on the GaN channel through the bi-layer passivation, the carrier transfer characteristics were improved in terms of carrier concentration at the AlGaN/GaN interface, as well as carrier mobility and sheet resistance compared to the high compressive stress condition. These results show that the mechanical stress engineering via optimized passivation process is a promising technique for the improvement of the device performance in GaN-based MISHEMTs.

Spatial control of cocatalysts and elimination of interfacial defects towards efficient and robust CIGS photocathodes for solar water splitting

Modifying TiO2-protected CIGS/CdS photocathodes: spatially controlled Pt cocatalysts accelerate the surface HER reaction, while the Al2O3passivation layer eliminates interfacial defects.

Abnormal Bias-Temperature Stress and Thermal Instability of $\beta$ -Ga2O3 Nanomembrane Field-Effect Transistor

In this paper, we report on the electrical and thermal instability of $\beta $ -Ga2O3 nanomembrane field-effect transistor with a bottom-gate configuration. The fabricated device exhibits high electrical performance of field-effect mobility of up to 60.9 cm2/ $\text{V}\cdot \text{s}$ , on/off-current ratio of 109, and subthreshold slope of 210 mV/dec. However, we observe abnormal positive threshold voltage ( ${V} _{\mathrm{ TH}}$ ) shifts under negative bias-temperature stress at an elevated operating temperature of 80 °C as well as under temperature-dependent transfer characteristics up to 200 °C. This abnormal instability is significantly influenced by the surface depletion effect, and is discussed using energy band diagram. The opposite ${V} _{\mathrm{ TH}}$ shift was achieved by applying atomic-layer deposited Al2O3 passivation layer.

Minimizing Light-Induced Degradation of the Al2O3 Rear Passivation Layer for Highly Efficient PERC Solar Cells

Commercializing a highly efficient passivated-emitter-and-rear-cell solar cell requires high passivation quality and stability of the cell's Al2O3 layer. This paper reports on light-induced degradation (LID) of the Al2O3 layer and the effects of post-annealing temperatures after light soaking on the passivation quality. To understand the LID phenomenon of the Al2O3 passivation layer, we used a Ga-doped Si wafer that prevented boron-oxygen LID effects. The fabrication process was carried out on large-area (156 × 156 mm2), commercially available, (100)-oriented Ga-doped Czochralski(Cz) Si wafers in the pilot line. Before and after light soaking, the effective lifetime was measured using Sinton's quasi-steady-state photoconductance as a function of annealing temperature. Chemical binding structures near the interface of the Al2O3 film and Si wafer were investigated using X-ray photoelectron spectroscopy (XPS). The passivation quality and light-induced degradation showed the best performance at an annealing temperature of 600°C. Analysis of XPS data revealed that the chemical binding structures at the interface of the Al2O3 layer and Si wafer were stabilized by optimizing the annealing condition of the Al2O3 layer. By optimizing an industrially feasible Al2O3 passivation process, an efficiency of 20.1% was achieved on large-area, commercial-grade Cz c-Si wafers.

Room-Temperature-Processed Flexible Amorphous InGaZnO Thin Film Transistor.

A room-temperature flexible amorphous indium-gallium-zinc oxide thin film transistor (a-IGZO TFT) technology is developed on plastic substrates, in which both the gate dielectric and passivation layers of the TFTs are formed by an anodic oxidation (anodization) technique. While the gate dielectric Al2O3 is grown with a conventional anodization on an Al:Nd gate electrode, the channel passivation layer Al2O3 is formed using a localized anodization technique. The anodized Al2O3 passivation layer shows a superior passivation effect to that of PECVD SiO2. The room-temperature-processed flexible a-IGZO TFT exhibits a field-effect mobility of 7.5 cm2/V·s, a subthreshold swing of 0.44 V/dec, an on-off ratio of 3.1 × 108, and an acceptable gate-bias stability with threshold voltage shifts of 2.65 and -1.09 V under positive gate-bias stress and negative gate-bias stress, respectively. Bending and fatigue tests confirm that the flexible a-IGZO TFT also has a good mechanical reliability, with electrical performances remaining consistent up to a strain of 0.76% as well as after 1200 cycles of fatigue testing.

Interface Manipulation to Improve Plasmon-Coupled Photoelectrochemical Water Splitting on α-Fe2 O3 Photoanodes.

The plasmon resonance effect of metal nanoparticles (NPs) offers a promising route to improve the solar energy conversion efficiency of semiconductors. In this study, it is revealed that hot electrons generated by the plasmon resonance effect of Au NPs tend to inject into the surface states instead of the conduction band of Fe2 O3 photoanodes, and then severe surface recombination occurs. Such an electron-transfer process seems to be independent of external applied potentials, but is sensitive to metal-semiconductor interface properties. Passivating the surface states of Fe2 O3 with a noncatalytic Al2 O3 layer can construct an effective resonant energy-transfer interface between Ti-doped Fe2 O3 (Ti-Fe2 O3 ) and Au NPs. In such a Ti-Fe2 O3 /Al2 O3 /Au electrode configuration, the enhanced photoelectrochemical (PEC) water-splitting performance can be attributed to the following two factors: 1) in the non-light-responsive wavelength range of Au NPs, both the relaxing Fermi pinning effect of the Al2 O3 passivation layer and the higher work function of Au enlarge band bending; thus promoting the charge separation; and 2) in the light-responsive wavelength range of Au NPs, the effective resonant energy transfer contributes to light harvesting and conversion. The interface manipulation proposed herein may provide a new route to design efficient plasmonic PEC devices for energy conversion.

A Hybrid Gate Dielectrics of Ion Gel with Ultra-Thin Passivation Layer for High-Performance Transistors Based on Two-Dimensional Semiconductor Channels

We propose a hybrid gate structure for ion gel dielectrics using an ultra-thin Al2O3 passivation layer for realizing high-performance devices based on electric-double-layer capacitors. Electric-double-layer transistors can be applied to practical devices with flexibility and transparency as well as research on the fundamental physical properties of channel materials; however, they suffer from inherent unwanted leakage currents between electrodes, especially for channel materials with low off-currents. Therefore, the Al2O3 passivation layer was introduced between the metal electrodes and ion gel film as a leakage current barrier; this simple approach effectively reduced the leakage current without capacitance degradation. In addition, we confirmed that a monolayer MoS2 transistor fabricated with the proposed hybrid gate dielectric exhibited remarkably enhanced device properties compared to a transistor using a normal ion gel gate dielectric. Our findings on a simple method to improve the leakage current properties of ion gels could be applied extensively to realize high-performance electric-double-layer transistors utilizing various channel materials.

Replacing the Al2O3 Shell on Al Particles with an Oxidizing Salt, Aluminum Iodate Hexahydrate. Part II: Synthesis

Improvements in the reactivity, measured in terms of flame speed, for aluminum-based energetic mixtures are increased by a factor of 2–3 by replacing the Al2O3 passivation layer of aluminum (Al) nanoparticles with aluminum iodate hexahydrate (AIH), an oxidizing salt. The Al–AIH nanoparticles are examined under transmission electron microscopy. An AIH passivation shell surrounding the Al core particle is a more reactive composite structure than Al2O3 passivation around Al which facilitates increased reaction rates with flame speeds as high as 3200 m/s. Flame speed measurements are used to show that reaction rates in AIH mixtures are determined by the AIH/Al2O3 ratio, oxygen balance, and β-HIO3. Further optimization of these properties will ultimately boost significant increases in the reaction rates of the energetic materials presented in this article.

Electrical properties and thermal stability in stack structure of HfO2/Al2O3/InSb by atomic layer deposition

Changes in the electrical properties and thermal stability of HfO2 grown on Al2O3-passivated InSb by atomic layer deposition (ALD) were investigated. The deposited HfO2 on InSb at a temperature of 200 °C was in an amorphous phase with low interfacial defect states. During post-deposition annealing (PDA) at 400 °C, In–Sb bonding was dissociated and diffusion through HfO2 occurred. The diffusion of indium atoms from the InSb substrate into the HfO2 increased during PDA at 400 °C. Most of the diffused atoms reacted with oxygen in the overall HfO2 layer, which degraded the capacitance equivalent thickness (CET). However, since a 1-nm-thick Al2O3 passivation layer on the InSb substrate effectively reduced the diffusion of indium atoms, we could significantly improve the thermal stability of the capacitor. In addition, we could dramatically reduce the gate leakage current by the Al2O3 passivation layer. Even if the border traps measured by C–V data were slightly larger than those of the as-grown sample without the passivation layer, the interface trap density was reduced by the Al2O3 passivation layer. As a result, the passivation layer effectively improved the thermal stability of the capacitor and reduced the interface trap density, compared with the sample without the passivation layer.

Deleterious electrostatic interaction in silicon passivation stack between thin ALD Al2O3 and its a-SiNX:H capping layer: numerical and experimental evidences

This study focuses on the electrostatic interaction between the ALD Al2O3 passivation layer and the PECVD a-SiNX:H capping layer, while reducing ALD Al2O3 thickness. The first one embeds negative fixed charges while the second is well known to possess a fixed charge density with an opposite polarity. We reduced the Al2O3 thickness from 20 to 2 nm while keeping constant the a-SiNX:H thickness. To increase the magnitude of the field effect passivation provided by Al2O3, we used an original light-induced field effect enhancement strategy. QSS-PC was used to quantify the initial passivation properties. We monitored the evolution of the passivation quality under low-intensity light-soaking until its stabilization. We report here a minority carrier lifetime enhancement up to 900% and surface recombination velocity reduction below 10 cm.s-1. The evidence of field effect compensation at c-Si surface due to a-SiNX:H positive charges has been supported by numerical simulations (SILVACO ATLAS). While keeping the parameters of the a-SiNX:H layer constant, the configuration of the Al2O3 layer (thickness and fixed charge density) were varied. These results allow us to conclude that in order to use thinner Al2O3 passivation layer (2 nm), ideal capping layer has to be free of positive fixed charges and to release enough hydrogen at desired temperature to ensure the chemical passivation.

In Situ Growth of Al2O3 as a Passivation and Antireflection Layer on TiO2-Based MSM Photodetectors

The in situ growth of Al2O3 on TiO2 by ultrasonic spray pyrolysis deposition is presented in this paper. Here, Al2O3 is used as the passivation and the antireflection layer. TiO2-based photodetectors (PDs) with Al2O3, SiO2, and no passivation layers were studied. It was found that the PD without the passivation layer has the highest dark current and photocurrent due to high internal photoconductive gain related to the reaction between the oxygen molecule and TiO2. The PDs with Al2O3 and SiO2 passivation layers suppress the internal photoconductive gain and show stable $I$ – $V$ characteristics after the PDs are exposed to air for 30 days. The device with the Al2O3 passivation layer showed the most stable $I$ – $V$ characteristics and the highest detectivity and the shortest response time among the three devices.

Enhanced electrical and optical properties of single-layered MoS2 by incorporation of aluminum

Electrical and optical enhancements of single-layer semiconducting materials such as transition metal dichalcogenides have recently been studied to achieve sensitive properties via external treatments, such as the formation of organic/inorganic protecting layers on field-effect transistors (FETs), thermal annealing, and nano-dot doping of sensors and detectors. Here, we propose a new analytical approach to electrical and optical enhancement through a passivation process using atomic layer deposition (ALD), and demonstrate a synthesized MoS2 monolayer incorporated with Al atoms in an Al2O3 passivation layer. The incorporated Al atoms in the MoS2 monolayer are clearly observed by spherical aberration-corrected scanning transmission electron microscopy (Cs-STEM) and TEM-energy-dispersive X-ray spectroscopy results. We demonstrate that the chemically incorporated FETs exhibit highly enhanced mobilities of approximately 3.7 cm2·V−1·s−1, forty times greater than that of as-synthesized MoS2, with a three-fold improvement in the photoluminescence properties.

The Stability Effect of Atomic Layer Deposition (ALD) of Al<sub>2</sub>O<sub>3</sub> on CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> Perovskite Solar Cell Fabricated by Vapor Deposition

The perovskite solar cells (PSCs) with Al2O3 passivation layer were fabricated and characterized. The PSC have some advantages of easier and cheaper fabrication process than that of conventional Si solar cells, III-V compound semiconductor solar cells, and organic solar cells. The perovskite light harvester, CH3NH3PbI3, was deposited by vapor deposition on [compact TiO2 / F-doped tin oxide (FTO) / glass]. The advantage of vapor deposition over solution process is expected to be able to offer the thin film with smoother surface over larger area. Then, Al2O3 passivation layer was deposited by atomic layer deposition (ALD) on the CH3NH3PbI3 light harvester. Al2O3 passivation layer was expected to prevent the CH3NH3PbI3 light harvester from oxidation and improve the solar cell efficiency, and ALD has been one of the most effective methods to deposit Al2O3 thin film for last 25 years. The atomic layer deposited Al2O3 layer thickness was optimized from the solar cell characterization. The optimized power conversion efficiency (PCE) and Al2O3 thickness were ~8.0 % and ~10.0 nm, respectively.