High-temperature Annealing Process Research Articles

Ge-ion implantation and activation in (100) β-Ga2O3 for ohmic contact improvement using pulsed rapid thermal annealing

In this work, we analyze the optimum annealing conditions for the activation of Ge-implanted β-Ga2O3 in order to reach low ohmic contact resistances. The experiments involved the use of a pulsed rapid thermal annealing treatment at temperatures between 900 and 1200 °C in nitrogen atmosphere. Our investigations show remarkable changes in the surface morphology involving increased surface roughness after high-temperature annealing above 1000 °C as well as a significant redistribution of the implanted Ge. Nevertheless, the specific contact resistance is strongly reduced by one order of magnitude after annealing at 1100 °C, reaching a record value of 4.8 × 10−7 Ω cm2 at an implantation activation efficiency of 14.2%. The highest activation efficiency of 19.2% and lowest sheet resistances were reached upon annealing at 1200 °C, which, in turn, showed inferior ohmic contact properties due to a severe increase of the surface roughness. Our results verify the high potential of applying high-temperature annealing processes above 1000 °C after Ge implantation for reaching low ohmic contact resistances to β-Ga2O3.

Unveiling the Enhanced Electrochemical Performance of LiNi0.5Mn0.3Co0.2O2 sol-gel coated with Li-La-Zr-O based gel

The LiNi0.5Mn0.3Co0.2O2 (NMC532) cathode surface has been coated with LLZO using the citric acid-aided sol-gel technique by adjusting the coating ratio and the annealing temperature. As a result, a thin coating layer is obtained on the cathode surface. LaMO3 formation is observed due to the diffusion of lanthanum ions during the high-temperature annealing process. Electrochemical examinations demonstrated that the electrochemical behaviour of coated samples improved compared to the uncoated sample. In particular, samples coated with 2 % LLZO with annealing temperatures higher than 700 °C deliver a desirable capacity retention of 92 % at 0.1 C after 100 cycles and an improved discharge capacity of 102 mA h g−1 at 1 C. Furthermore, electrochemical impedance spectroscopy measurement reveals that 2 % LLZO-coated samples with annealing above 700 °C have lower interface resistance than pristine NMC532. These findings provide a practical understanding of the NMC/LLZO coating interface in terms of phase formation and chemical composition and its effect on the electrochemical performance.

Role of Oxygen Incorporation in High Temperature Annealed AlGaN

High‐temperature annealing (HTA) is a powerful technique to decrease dislocation density in AlN, which can also be applied on AlGaN. This work investigates the impact of using sapphire and AlN as a material cover during the face‐to‐face HTA process on AlxGa1−xN (0.55 < x < 0.93) properties. Before HTA, the threading dislocation density (TDD) in the AlGaN for all xAl was about 6.0 × 109 cm−2. Meanwhile, after HTA, the sapphire cover led to a further reduction of the TDD at 5.7 × 109 cm−2 for the lowest xAl and 1.4 × 109 cm−2 for the highest xAl in comparison to the AlN cover. In most cases, strain relaxation increased by HTA, especially with the sapphire cover. Furthermore, increased optical absorption in HTA AlGaN can be lessened by the sapphire cover. Such absorption compromises the performance of UV LEDs which usually emit through the substrate. These advantages of sapphire over AlN as the cover in the HTA process are associated with additional oxygen incorporation into the AlGaN, most probably from the surface of the sapphire cover.

Effect of High-Temperature Annealing on Raman Characteristics of Silicon Nanowire Arrays

We demonstrate two distinct experimental processes involving the large-area growth of ordered and disordered silicon nanowire arrays (SiNWs) on a p-type silicon substrate using the metal-assisted chemical etching method. The two processes are based on the etching of monocrystalline silicon wafers by randomly distributed Ag films and ultra-thin Au films with ordered nano-mesh arrays, respectively, wherein the growth of SiNWs is implemented using a specific proportion of a HF-containing solution at room temperature. In this study, the microstructural change mechanisms for the two morphologically different arrays before and after annealing were investigated using Raman spectra. The effects of various mechanisms on the observed Raman scattering peak’s deviation from symmetry, redshift and broadening were analyzed. The evolution of the unstable amorphous structures of nanoscale materials during the high-temperature annealing process was observed via high-resolution scanning electron microscope (SEM) observations. The scattering peak parameters determined from the Raman spectra led to conclusions concerning the various mechanisms by which high-temperature annealing influences the microstructures of the two morphologically different SiNWs fabricated on the p-type silicon substrate. Therefore, the deviation of SiNWs from the monocrystalline silicon scattering peak at 520.05 cm−1 when changing the diameter of the nanowire columns was calculated to further analyze the effect of thermal annealing on Raman characteristics.

Chemical Mechanical Polishing of MgO Substrate and Its Effect on Fabrication of Atomic Step-Terrace Structures on MgO Surface by Subsequent High-Temperature Annealing

Single-crystalline MgO is used as a substrate for the deposition of various functional thin films. The present study focused on the development of a complete sequence of fabricating atomic step-terrace structures on the MgO substrate via a method that includes grinding, precise mechanical polishing, chemical mechanical polishing (CMP), and high-temperature annealing. The effect of a damage-free surface pretreatment on the subsequent high-temperature annealing was investigated. An atomically smooth and damage-free MgO substrate surface with an average surface roughness of 0.05 nm was obtained via a CMP process using a colloidal silica slurry. Atomic step-terrace structures were formed on the substrate after the high-temperature annealing process at 1000 °C for 20 h under atmospheric air. The obtained step height was 0.20 nm, which corresponds to one-half the unit cell of an MgO crystal (0.21 nm). By contrast, when a mechanically damaged MgO substrate was subjected to the annealing process, Ca segregation was observed on the annealed surface, without the formation of an atomic step-terrace structure. CMP was found to be necessary prior to high-temperature annealing to attain atomic step-terrace structures and to avoid the out-diffusion of impurities in the MgO bulk crystals.

Manipulation of the coercivity of FeCoCr films through artificial defects engineering based on Bi doping

FeCoCr thin films have been considered as promising candidates for magnetic code disk materials used in high-precision magnetic rotary encoders. However, realizing high coercivity with a sufficient remanence is a critical issue for magnetic recording stability from the point of view of practical applications. We prepared Bi-free and Bi-doped FeCoCr(250 nm)/Ta(10 nm) films on Si substrates using magnetron sputtering followed by vacuum annealing at 650 °C for 30 min. The in-plane coercivity of Bi-free and Bi-doped FeCoCr samples are 414 Oe and 930 Oe respectively, indicating that the coercivity can be greatly enhanced by Bi doping. X-ray photoelectron spectroscopy (XPS) reveals that Bi atoms diffuse to the film surface and then sublimate during high-temperature annealing process. Positron annihilation spectroscopy (PAS) indicates that the diffusion of Bi atoms increases the density of defects in the film. Scanning transmission electron microscopy (STEM) analysis shows that the diffusion behavior of Bi atoms not only refines the grain size but also results in a uniform distribution of the Fe-Co-rich (α1 phase) phase with the Cr-rich (α2 phase) phase. Magnetic force microscopy (MFM) analysis observes that the introduction of Bi decreases the magnetic domain size and increases the magnetic domain density resulting in the enhancement of coercivity.

Low-Temperature Phase-Transition for Compositional-Pure α-FAPbI3 Solar Cells with Low Residual-Stress and High Crystal-Orientation.

Transition of δ-phase formamidinium lead triiodide (δ-FAPbI3 ) to pure α-phase FAPbI3 (α-FAPbI3 ) typically requires high processing temperature (150 °C), which often results in unavoidable residual stress. Besides, using methylammonium chloride (MACl) as additive in fabrication will cause MA residue in the film, compromising the compositional purity. Here, a stress-released and compositional-pure α-FAPbI3 thin-film is fabricated using 3-chloropropylammonium chloride (Cl-PACl) by two-step annealing. The 2D template of n = 2 can preferentially form in perovskite with the introduction of Cl-PACl at a temperature as low as 80 °C. Such a 2D template can guide the free components to form ordered α-FAPbI3 and promote the transition of the formed δ-FAPbI3 to α-FAPbI3 by reducing the phase transition energy. As a result, the obtained perovskite films via low-temperature phase-transition have a high degree of crystal orientation and reduced residual stress. More importantly, most of the Cl-PACl is volatilized during the subsequent high-temperature annealing process accompanied by the disintegration of the 2D templates. The residual trace of Cl-PA+ is mainly concentrated at the grain boundary near the perovskite surface layer, stabilizing α-FAPbI3 and passivating defects. Perovskite solar cell based on pure α-FAPbI3 achieves a power conversion efficiency of 23.03% with excellent phase stability and photo-stability.

Band gap and Morphology Engineering of Hematite Nanoflakes from an Ex Situ Sn Doping for Enhanced Photoelectrochemical Water Splitting.

In this article, we report a simple ex situ Sn-doping method on hematite nanoflakes (coded as MSnO2-H) that can protect the nanoflake (NF) morphology against the 800 °C high-temperature annealing process and activate the photoresponse of hematite until 800 nm wavelength excitation. MSnO2-H has been fabricated by dropping SnCl4 ethanol solution on hematite nanoflakes homogeneously grown over the conductive FTO glass substrate and annealed at 500 °C to synthesize the SnO2 nanoparticles on hematite NFs. The Sn-treated samples were then placed in a furnace again, and the sintering process was conducted at 800 °C for 15 min. During this step, structure deformation of hematite occurs normally due to the grain boundary motion and oriented attachment. However, in the case of MSnO2-H, the outer SnO2 nanoparticles efficiently prevented a shape deformation and maintained the nanoflake shape owing to the encapsulation of hematite NFs. Furthermore, the interface of hematite/SnO2 nanoparticles became the spots for a heavy Sn ion doping. We demonstrated the generation of the newly localized states, resulting in an extension of the photoresponse of hematite until 800 nm wavelength light irradiation. Furthermore, we demonstrated that SnO2 nanoparticles can effectively act as a passivation layer, which can reduce the onset potential of hematite for water splitting redox reactions. The optimized MSnO2-H nanostructures showed a 2.84 times higher photocurrent density and 300 mV reduced onset potential compared with a pristine hematite nanoflake photoanode.

Non-polar a-plane AlN epitaxial films on r-plane sapphire with greatly reduced defect densities obtained by high-temperature annealing

This study addresses the difficulty of obtaining high crystalline quality non-polar a-plane AlN films grown epitaxially on r-plane sapphire substrates by applying a high-temperature annealing process to films grown via standard-temperature metal organic chemical vapor deposition. Atomic force microscopy results demonstrate the occurrence of a significant recrystallization process in the AlN films during annealing. Raman spectroscopy measurements reveal that the AlN films are subject to a transition from tensile strain to compressive strain after the annealing process. Transmission electron microscopy analyses demonstrate that the non-polar a-plane AlN films provide an appropriately low dislocation density of 3.7 × 109 cm−2.

Improvement of Device Characteristics of Low Temperature IGZO Thin-film Transistors through Laser Post Annealing

High-performance thin-film transistors (TFTs) produced at low temperatures are required for ultrahigh- resolution and flexible display applications. The scientific community has been studying unconventional techniques to investigate low voltage flexible devices and low power flexible circuits for the past decade. In particular, metal oxide semiconductors, such as indium gallium zinc oxide (IGZO), have made significant progress as amorphous silicon replacements for electronics and commercial displays. On the other hand, developing metal oxide transistors with low processing temperatures remains a difficulty. The hightemperature annealing process causes very instability in the plastic substrate. Here, we introduce IGZO TFTs that shows enhanced electrical properties environmental stability by laser post-annealing. After annealing process, the laser post-annealing process was given at 80 MHz, pulse width 140 fs, for 50 seconds. The improved electrical characteristics of this laser post-annealed IGZO TFTs were: 9.03 cm<sup>2</sup>/Vs; 2.2×10<sup>7</sup> on/off current ratio. The IGZO TFT to which laser post-annealing was applied had a flat surface, and it was confirmed that the combination of internal metal and oxygen was urged, and the leakage current problem was improved by suppressing excessive generation of oxygen vacancy. Furthermore, the voltage transfer curve was measured after fabricating the N-MOS logic inverter circuit, this inverter showed a value of 80.8% the total noise margin.

Component Design of Environmentally Friendly High-Temperature Resistance Coating for Oriented Silicon Steel and Effects on Anti-Corrosion Property

Oriented silicon steel is vital for power transformer cores, while the high-temperature annealing process limits the industrialization of environmentally friendly coatings on the surface. In this paper, the high-temperature binders Al(H2PO4)3 solution and silica sol were introduced innovatively. They condensed into macromolecular polymer chains, network structures and SiO2 particles at high temperatures, providing high-temperature stability and adhesion. The influence of types of silica sol, additives and functional fillers on the corrosion resistance of the coating was studied. The prepared environmentally friendly inorganic insulating coating for oriented silicon steel has excellent corrosion resistance after curing at 475 °C and annealing at 800 °C, which was matched with the currently rolling process of oriented silicon steel. The salt-spray resistance can last for more than 24 h and up to 72 h.

Effect of capping layer on the ferroelectricity of hafnium oxide

In this work, we investigate the effect of a capping layer of aluminum oxide (AlOx) on dopant-free hafnium-oxide (HfO2) ferroelectric layer. According to our experimental results, the AlOx-capped HfO2 ferroelectric capacitor exhibits the significant improvement on ferroelectric polarization strength and also presents a comparable electrical stress resistance in comparison with control HfO2 ferroelectric capacitor with a very weak ferroelectric hysteresis. An additional nitrogen treatment on AlOx capping layer effectively alleviate the stress-induced generation of defect traps near the interface of tantalum nitride (TaN) electrode under negative-bias voltage stress. Therefore, the performance improvement can be ascribed to the introduction of AlOx capping layer and well-controlled nitrogen plasma treatment to improve interface traps and stabilize the ferroelectric phase transformation during high-temperature annealing process.

A study on repeatable and universal growth morphology optimization for nanowires grown on Si substrates

In this work, a series of NWs growths with different treatments for substrate surface have been carried out to study growth morphology optimization for NWs grown on Si substrates. A substrate treatment method of high-temperature annealing combined with thin oxide layer formed on the substrate surface has been developed. It is found that a lot of crystal defects exist in random locations of common substrates surface which make it difficult to grow NWs, but easy to form parasitic islands. XRD and AFM show that high-temperature annealing process can effectively eliminate most of the crystal defects in the substrates, inhibit the formation of parasitic islands. Combined with forming thin natural oxide layer on the substrate surface, the density of InAs NWs can be increased, the growth morphology uniformity of InAs NWs on Si substrates can be improved and parasitic islands are rarely formed on the substrates surface at all. In order to verify the effectiveness and universality of this method, another experiment of InGaAs NWs grown at different temperatures obtained excellent growth results as well. Therefore, this substrate treatment method has good effectiveness, repeatability and universality in optimizing the growth morphology of NWs.

Considerations on the kinetic correlation between SiC nitridation and etching at the 4H-SiC(0001)/SiO2 interface in N2 and N2/H2 annealing

The kinetics of the SiC surface nitridation process of high-temperature N2 annealing was investigated with a 4H-SiC(0001)/SiO2 structure based on the correlation between the rates of N incorporation and SiC consumption induced by SiC etching. During the early stage of the annealing process, the rate-limiting step for N incorporation would be the removal of the topmost C atoms in the slow-etching case, while it would be another reaction step, probably the activation process of N, in the fast-etching case. The SiO2 layer thickness and the annealing ambient gas, which serve as the parameters affecting the SiC etching rate, would determine the N incorporation rate according to the kinetic correlation between the N incorporation and SiC etching. The SiC consumption observed during high-temperature annealing in N2 and N2/H2 atmospheres would be induced by active oxidation by residual O2 or H2O in the ambient gas, which would lead to SiC surface roughening.

Effect of 2 MHz frequency power applied to the substrate for low-temperature silicon nitride thin film deposition

Silicon nitride (SiNx) thin films were deposited at a low temperature of 80 °C using a dual-frequency plasma-enhanced chemical vapor deposition (PECVD) equipment. The density of the thin film was increased by 17% by increasing the low-frequency (LF) power of 2 MHz applied to the lower electrode to 100 W separately from the plasma generated by the 180 W power of 13.56 MHz applied to the upper electrode. The advantage of this dual-frequency PECVD process is that even if it is deposited at a low temperature, it shows similar effects to high-temperature deposition or post-deposition annealing process. Due to the LF power applied to the substrate, the hydrogen concentration in the deposited SiNx thin film decreases, which in turn leads to an increase in the film density. The increase in SiNx thin film density eventually results in a 21% increase in dielectric constant. It was shown that the use of SiNx thin films with improved properties as a dielectric layer of a thin film transistor can increase mobility and on-off ratio and reduce leakage current and subthreshold swing of the transistor.

Coercivity and remanence enhancement in hot-deformed Nd-Fe-B magnets by high-temperature short-term annealing process

It is challenging to simultaneously improve the coercivity, remanence and squareness factors of sintered and hot-deformed magnets, because of the complicated influences by various microstructure factors. In this work, we demonstrate that the coercivity, remanence and squareness factor of hot-deformed Nd-Fe-B magnet can be enhanced simultaneously by high-temperature short-term annealing process. The coercivity of the hot-deformed sample increased from 1.05 T to a maximum of 1.28 T after annealing at 800 °C, and decreased to 0.87 T at 900 °C. The remanence of the hot-deformed sample increased continuously from 1.41 to 1.49 T as the annealing temperature increased to 900 °C. The calculated squareness value firstly increased from 0.91 to 0.97 at 850 °C, then decreased to 0.74 at 900 °C. An block-shaped Nd-Fe-rich phase, Nd6(Fe,Co)13Ga, was identified in hot-deformed sample. The improvement of coercivity is due to the melting and infiltration of Nd6(Fe,Co)13Ga phase from the surface of powder flakes into the grain boundaries during annealing process. The slightly anisotropic growth of Nd2Fe14B grains results in an improved grain alignment thus the enhanced remanence. Furthermore, the melting point of Nd6Fe13Ga (810 ℃) and Nd6(Fe,Co)13Ga (760 ℃) phases were confirmed by DSC, indicates that adding a small amount of Co element in Nd6Fe13Ga compound can significantly reduce its melting point. Due to the micrometer scale infiltration distance from powder flake surface into the grain boundaries, a balance between infiltration within the powder flakes and grain growth can be achieved under the present processing conditions. This opens up a new route to improve the coercivity, remanence and squareness factor simultaneously for hot-deformed Nd-Fe-B sample.

MoO3 Nanoparticle Coatings on High-Voltage 5 V LiNi0.5Mn1.5O4 Cathode Materials for Improving Lithium-Ion Battery Performance.

To reduce surface contamination and increase battery life, MoO3 nanoparticles were coated with a high-voltage (5 V) LiNi0.5Mn1.5O4 cathode material by in-situ method during the high-temperature annealing process. To avoid charging by more than 5 V, we also developed a system based on anode-limited full-cell with a negative/positive electrode (N/P) ratio of 0.9. The pristine LiNi0.5Mn1.5O4 was initially prepared by high-energy ball-mill with a solid-state reaction, followed by a precipitation reaction with a molybdenum precursor for the MoO3 coating. The typical structural and electrochemical behaviors of the materials were clearly investigated and reported. The results revealed that a sample of 2 wt.% MoO3-coated LiNi0.5Mn1.5O4 electrode exhibited an optimal electrochemical activity, indicating that the MoO3 nanoparticle coating layers considerably enhanced the high-rate charge–discharge profiles and cycle life performance of LiNi0.5Mn1.5O4 with a negligible capacity decay. The 2 wt.% MoO3-coated LiNi0.5Mn1.5O4 electrode could achieve high specific discharge capacities of 131 and 124 mAh g−1 at the rates of 1 and 10 C, respectively. In particular, the 2 wt.% MoO3-coated LiNi0.5Mn1.5O4 electrode retained its specific capacity (87 mAh g−1) of 80.1% after 500 cycles at a rate of 10 C. The Li4Ti5O12/LiNi0.5Mn1.5O4 full cell based on the electrochemical-cell (EL-cell) configuration was successfully assembled and tested, exhibiting excellent cycling retention of 93.4% at a 1 C rate for 100 cycles. The results suggest that the MoO3 nano-coating layer could effectively reduce side reactions at the interface of the LiNi0.5Mn1.5O4 cathode and the electrolyte, thus improving the electrochemical performance of the battery system.

Sulfur-Bridged Bonds Boost the Conversion Reaction of the Flexible Self-Supporting MnS@MXene@CNF Anode for High-Rate and Long-Life Lithium-Ion Batteries.

Manganese sulfide (MnS) has been found to be a suitable electrode material for lithium-ion batteries (LIBs) owing to its considerable theoretical capacity, high electrochemical activity, and low discharge voltage platform, while its poor electrical conductivity and severe pulverization caused by volume expansion of the material limit its practical application. To improve the rate performance and cycle stability of MnS in LIBs, the structure-control strategy has been used to design and fabricate new anode materials. Herein, the MnS@MXene@CNF (MMC, CNFs means carbon nanofibers) electrode has been prepared by electrospinning and a subsequent high-temperature annealing process. The MMC electrode exhibits excellent cyclic stability with a capacity retention rate close to 100% after 1000 cycles at 1000 mA/g and an improved rate performance with a specific capacity up to 500 mAh/g at a high current density of 5000 mA/g, much higher than the 308 mAh/g of the MnS@CNF (MC) electrode. The elevated electrochemical performance of the MMC electrode not only benefits from the unique structure of MnS nanoparticles evenly dispersed in the well-designed flexible self-supporting three-dimensional (3D) CNF network but, more importantly, also benefits from the formation of sulfur-bridged Mn-S-C bonds at the MnS/MXene interface. The newly formed bonds between MnS and MXene nanosheets can stabilize the structure of MnS near the interfaces and provide a channel for fast charge transfer, which notably increase both the reversibility and the rate of the conversion reaction during the charge/discharge process. This work may pave a new path for designing stable and self-supporting anodes for high-performance LIBs.

A-Site Substitute for Fabricating All-Inorganic Perovskite CsPbCl3 with Application in Self-Powered Ultraviolet Photodetectors.

Because of its stable chemical properties and wide band gap, CsPbCl3 perovskite has shown great application prospects in ultraviolet photodetectors (UPDs). However, the poor solubility of CsCl in organic solvents impedes the fabrication of high-quality CsPbCl3 films. Herein, we introduced an A-site substitute route for fabricating a high-quality CsPbCl3 microcrystalline (MC) film by spin-coating cesium acetate on a MAPbCl3 MC film followed by a high-temperature annealing process. To enhance the device performance of the FTO/SnO2/CsPbCl3 MCs/carbon structure UPD, a pressure-assisted annealing strategy was carried out, which reduced the void density and surface roughness of the microcrystal film. Finally, our optimized PDs showed high device performances with an on/off ratio of 6 × 104, a responsivity of 0.13 A W-1, a detectivity of as high as 1.07 × 1012 Jones, and a rise/fall time of 10/24 μs. Moreover, our unpacked PDs showed good storage and light stability. Our results lay a foundation for the application of all inorganic perovskite in the ultraviolet region.

Flexible Ferroelectric Hafnia-Based Synaptic Transistor by Focused-Microwave Annealing.

Hafnia-based ferroelectric memory devices with excellent ferroelectricity, low power consumption, and fast operation speed have attracted considerable interest with the ever-growing desire for nonvolatile memory in flexible electronics. However, hafnia films are required to perform a high temperature (>500 °C) annealing process for crystallization into the ferroelectric orthorhombic phase. It can hinder the integration of hafnia ferroelectric films on flexible substrates including plastic and polymer, which are not endurable at high temperatures above 300 °C. Here, we propose the extremely low-temperature (∼250 °C) process for crystallization of Hf0.5Zr0.5O2 (HZO) thin films by applying a focused-microwave induced annealing method. HZO thin films on a flexible mica substrate exhibits robust remnant polarization (2Pr ∼ 50 μC/cm2), which is negligibly changed under bending tests. In addition, the electrical characteristics of a HZO capacitor on the mica substrate were evaluated, and ferroelectric thin film transistors (Fe-TFTs), using a HZO gate insulator, were fabricated on mica substrates for flexible synapse applications. Symmetric potentiation and depression characteristics are successfully demonstrated in the Fe-TFT memory devices, and the synaptic devices result in high recognition accuracy of 91.44%. The low-temperature annealing method used in this work are promising for forming hafnia-based Fe-TFT memory devices as a building block on a flexible platform.