High Temperature Post Annealing Research Articles

Influence of oxygen on the optical and electrical properties of magnetron-sputtered indium tin oxide thin films at ambient temperature

Indium Tin Oxide (ITO) thin films are commonly used as transparent conductive layers in the production of solar cells. ITO films are typically heat-treated at temperatures exceeding 200 °C after magnetron sputtering to optimize the physical, optical, and electrical characteristics for photovoltaic devices. This high temperature heating procedure greatly limits the use of potential substrates, particularly those comprised of low-temperature-rated polymers. Herein, we examine the physical, optical, and electrical transport effects of oxygen:argon plasmas during radio frequency magnetron sputtering of ITO on glass and flexible polymer surfaces without subsequent heat treatment. ITO thin films were characterized via sheet resistance testing, UV–Vis spectroscopy, X-ray diffraction, and scanning electron microscopy imaging. Sheet resistance measurements revealed an increase in surface resistance with increasing oxygen concentration during sputtering. UV–Vis optical transmittance measurements demonstrated an improvement in optical transmittance with an increase in oxygen concentration reaching a maximum transmittance at an oxygen concentration of 1-2%. Most importantly, it was discovered that producing bilayers of ITO with pure argon sputtered plasmas followed by oxygen:argon plasmas produced ITO thin films with suitable resistance and transmittance without the need for high temperature post annealing. These results highlight a methodology for the deposition of ITO thin films on temperature sensitive substrates for flexible photovoltaics and low-cost module production.

Greatly Improved Trapped Magnetic Fields of REBCO Melt-Grown Bulks Through Reductive High-Temperature Post-Annealing

We investigated the effects of high-temperature post-annealing on magnetic field-trapping properties of REBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">_y</i> melt-grown bulks composed of a single <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> -growth domain prepared by the single-direction melt growth (SDMG) method. High-temperature post-annealing at 900°C under moderately reductive atmosphere for readily oxygenated bulks greatly improved trapped fields with maintaining circular concentric distributions. Oxygen diffusion was found to be further accelerated after post-annealing as well. An enhancement ratio of the trapped field averaged over all bulks through this post-annealing was ∼40% in the present study. In particular, a DyBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">_y</i> bulk with 24.3 mm in diameter and 10.8 mm in thickness recorded a high trapped field of 1.09 T at 77 K.

Preparation of In0.5Sc1.5Mo3O12 nanofibers and its negative thermal expansion property

Orthorhombic In0.5Sc1.5Mo3O12 nanofibers were prepared by electrospinning followed by a heat treatment. The effects of post-annealing temperatures on the phase composition, microstructure and morphology were investigated by XRD, SEM, HRTEM and XPS. Negative thermal expansion (NTE) behaviors of the In0.5Sc1.5Mo3O12 nanofibers were analyzed by high-temperature XRD. Results indicate that the as-prepared In0.5Sc1.5Mo3O12 nanofibers show an amorphous structure with smooth and homogeneous shape. The average diameter of the as-prepared In0.5Sc1.5Mo3O12 nanofibers is around 515 nm. Well crystallized orthorhombic In0.5Sc1.5Mo3O12 nanofibers could be prepared after post-annealing at 550 °C for 2 h with an average diameter of about 192 nm. The crystallinity of In0.5Sc1.5Mo3O12 nanofibers gradually improved with the increase of annealing temperature. However, too high post-annealing temperature leads to a damage of sample's fiber structure. The high-temperature XRD results reveal that In0.5Sc1.5Mo3O12 nanofibers show an anisotropic NTE, and the coefficients of thermal expansion (CTEs) along a-axis and c-axis were −5.95 × 10−6 °C−1 and -3.54 × 10−6 °C−1, while the one along b-axis is 5.61 × 10−6 °C−1. The volumetric CTE of In0.5Sc1.5Mo3O12 nanofibers is −3.90 × 10−6 °C−1 and the linear one is 1.3 × 10−6 °C−1 in 25–700 °C.

Cerium-Doped Indium Oxide as a Top Electrode of Semitransparent Perovskite Solar Cells

Semitransparent perovskite solar cells (ST-PSCs) play a very important role in high-efficiency tandem solar cells and building integrated photovoltaics (BIPV). One of the main challenges for high-performance ST-PSCs is to obtain suitable top-transparent electrodes by appropriate methods. Transparent conductive oxide (TCO) films, as the most widely used transparent electrodes, are also adopted in ST-PSCs. However, the possible ion bombardment damage during the TCO deposition and the relatively high postannealing temperature usually required for high-quality TCO films is not conducive to improving the performance of the perovskite solar cells with low ion bombardment and temperature tolerances. Herein, cerium-doped indium oxide (ICO) thin films are prepared by reactive plasma deposition (RPD) at substrate temperatures below 60 °C. A high carrier mobility of 50.26 cm2 V-1 s-1, a low resistivity of 7.18 × 10-4 Ω·cm, and an average transmittance of 86.53% in the wavelength range of 400-800 nm and 87.37% in the wavelength range of 800-1200 nm are achieved. The RPD-prepared ICO film is used as a transparent electrode on top of the ST-PSCs (band gap ∼1.68 eV), and photovoltaic conversion efficiency (PCE) of 18.96% is achieved on the champion device.

Atomic tailoring of low-thermal-budget and nearly wake-up-free ferroelectric Hf0.5Zr0.5O2 nanoscale thin films by atomic layer annealing

In recent years, ferroelectric hafnium zirconium oxide (Hf0.5Zr0.5O2, HZO) has emerged as apromising candidate for nonvolatile memory and energy storage devices. A low thermal budget technique for achieving sub-10 nm HZO thin films with pronounced ferroelectricity is highly demanded for ferroelectric applications such asadvanced semiconductor technology nodes. In this paper, the atomic layer annealing (ALA) technique, which is thein situHe/Ar plasma treatment incorporated into the atomic layer deposition cycle, is demonstrated to achieve the transformation from amorphous to orthorhombic phase in sub-10 nm HZO layers without the need of any high-temperature post annealing. As compared with the ALA process conducted on each ZrO2monolayer, the ALA treatment performed on each HfO2monolayer is much preferred in terms of superior crystallinity and ferroelectric properties of the HZO thin films. Hence a high remanent polarization together with a nearly wake-up-free property are accomplished in the HZO layer. The study demonstrates ALA is an effective technique to realize the atomic tailoring ofcrystalline quality and ferroelectric/dielectric characteristics of nanoscale thin films at a low temperature, which is very favorable in a variety of applications including biomedical, wearable, and nanoelectronic devices, in which a low thermal budget process is required.

A flexible and transparent β-Ga2O3 solar-blind ultraviolet photodetector on mica

In the present work, we report a flexible transparent β-Ga2O3 solar-blind ultraviolet (UV) photodetector (PD) fabricated on a mica substrate. A laminated a-Ga2O3/Ga/a-Ga2O3 structure is thermally annealed at 1050 °C, forming a β-Ga2O3 film incorporating Ga nanospheres. A PD based on this nanocomposite film has a spectrum response peak at 250 nm, an extremely low dark current of 0.6 pA at a 10 V bias, a very high Ilight/Idark ratio of 3 × 106, and a fast recovery speed of less than 50 ms. Robust flexibility is demonstrated by bending tests and 10 000 cycles of a fatigue test with a radius as small as 8 mm. Compared to a room-temperature-fabricated flexible amorphous Ga2O3 (a-Ga2O3) PD, the flexible β-Ga2O3 PD on mica exhibits improved solar-blind UV photoresponse characteristics. The insertion of a gallium interlayer and treatment by high-temperature post annealing are proposed to contribute to a better stoichiometry and lattice order of the β-Ga2O3 thin film, as evidenced by the pronounced Raman peaks related to the GaI(OI)2 and GaIO4 vibration modes in β-phase Ga2O3. Our research is believed to provide a simple and practical route to achieving flexible transparent β-Ga2O3 solar-blind UV PDs, as well as other devices such as flexible transparent phototransistors and power rectifiers.

Ultra high hole mobility in Ge films grown directly on Si (1 0 0) through interface modulation

We have demonstrated an effective method to achieve ultra high mobility in the Ge films grown directly on Si (100) using molecular beam epitaxy (MBE). The Hall effect measurements revealed that the unintentionally doped Ge films have a hole mobility up to 1252 cm2/V·s at room temperature and 3855 cm2/V·s at 80 K. A proper combination of low temperature epitaxy and high temperature post annealing provides the opportunity on defect reduction and interface modulation. The periodic 90° interfacial misfit (IMF) array formed at the Ge/Si interface is believed to contribute to a preferential strain relieve at the interface and the ultra high mobility.

New deposition method of MgB2 thin film with thermal evaporation of Mg and sputtering of B

We are now developing a new in situ deposition process for MgB2 film as a candidate method to mass-produce MgB2 thin film superconducting tape. In the new method, a MgB2 film is deposited on a heated metal substrate by a hybrid deposition method, which consists of thermal evaporation of magnesium and sputtering of boron. By using the hybrid deposition method, the substrate temperature can raise from 250 to 350 °C, while its fluctuation is kept less than 1 °C, which will improve the quality and reproducibility of MgB2 film in mass production. The Jc of MgB2 film deposited by the hybrid deposition method at 20 K and self-field was more than 30,000 A mm−2, which was better than the results reported by the two-step in situ process using DC sputtering and 830 °C high-temperature post annealing [] or by the as-grown depostion using sputttering targets of Mg and B []. Although we obtained better Jc than other deposition methods that use sputtering process, the Jc is still lower than the value we obtained by using a co-evaporation method with electron beam (EB). We investigated the film structure and Jc–B–T properties of the film made by the hybrid deposition method and compared them with those of the film made by co-evaporation. From the analysis results, we think the reasons for the lower Jc are the larger amount of heterogeneous phases such as magnesium oxides in the film and the amorphous B phase under the MgB2. We expect to improve the the crystal qualities and superconductivities of the MgB2 film deposited by the new method by removing impurities in Ar gas during sputtering and thinning the B amorphous phase by increasing the Mg deposition rate in the initial stage of deposition.

Intense pulsed light sintering of vanadium dioxide nanoparticle films and their optical properties for thermochromic smart window

As cost-efficient and large-scalable fabrication, solution processing has been developed to prepare vanadium dioxide (VO2) films for thermochromic smart windows that can modulate infrared radiation in response to changes in ambient temperature while maintaining visible transmittance. Herein, we report for fabrication of VO2 films from ball-milled VO2 nanoparticle ink using intense pulsed light (IPL) sintering. The VO2 films on quartz substrates were prepared by spin coating. The prepared films were sintered by IPL in air with various voltages from 1400 to 2000 V with the fixed conditions of 4 ms, 400 pulses and 1 Hz. IPL sintering of VO2 nanoparticle ink led to granular films which were sintered at higher voltages since IPL irradiation was able to evaporate solvent including polymers in the ink, and sinter VO2 nanoparticles. The VO2 films IPL sintered at 2000 V exhibit luminous transmittance of over 46.3% and solar transmittance modulation of 11.2%. These results reveal that IPL sintering is substantial progress in terms of long-time and high-temperature post annealing for fabrication of solution-based thermochromic films.

Influence of annealing conditions on threading dislocation density in Ge deposited on Si by reduced pressure chemical vapor deposition

The influence of annealing conditions on the crystallinity of Ge deposited on Si(001) is investigated. Ge deposited with postannealing at 800 °C and 850 °C, five cycles of postannealing at 750 °C and 850 °C (temperature-swing postannealing) and several cycles of annealing at 800 °C or 850 °C during the Ge growth by interrupting the deposition step (cyclic annealing) are compared. To check the threading dislocation density (TDD) of the deeper part of the Ge, thinning by HCl vapor phase etching (VPE) followed by Secco defect etching is performed for 5 μm thick Ge of all three annealing variants. By comparing the TDD of the same Ge thickness with and without HCl VPE, TDD reduction by VPE is observed for the sample using the cyclic annealing process only. Lower TDD is observed at higher postannealing temperature. By the five cycles of temperature swinging, TDD becomes around a half compared to conventional postannealing at 850 °C. In the case of the cyclic annealing process significant improvement of TDD is observed with increasing Ge thickness. Even at a maximum temperature of 800 °C, the same or lower TDD levels were observed for higher than 2 μm thick Ge compared to that with five cycles of temperature-swing postannealing. For the sample with cyclic annealing at 800 °C, a lower Si diffusion length into Ge is also observed for the cyclic annealing process indicating a lower thermal budget. A lower amount of tilted Ge planes at the interface is confirmed showing higher crystal quality also in the deeper part of the Ge layer.

Effect of post-annealing in low oxidizing atmosphere on the properties of CeO2 buffer layer for coated conductors

CeO2-x thin films have been fabricated by chemical solution deposition (CSD) technique on bi-axial textured Ni5W substrates. The effect of post-annealing in moderate oxidizing atmosphere on the structure and texture of the film has been studied by varying temperature and CO2 concentration during the post-annealing process. The results show that the structure and texture stability of the CeO2-x film is heavily dependent on the post-annealing temperature. A high post-annealing temperature could lead to the change of cerium valence and even oxidation of Ni5W substrate. In addition, an excess amount of CO2 could cause the degeneration of texture degree and surface flatness of CeO2-x film because of the increase of oxygen vacancy defects and the production of carbonates. Except effective removal of residual carbon in films, therefore, the production of both the oxygen vacancy concentration and carbonates should be greatly controlled to improve the texture degree and surface flatness of CeO2-x films by adjusting the concentration of oxidizing gas and the heat-treatment temperature during the post-annealing process or the YBCO deposition process. Moreover, the CeO2-x film post-annealed at 700 °C in the mixture atmosphere with 1% CO2 show sharper texture and smoother surface because of the existence of small amount of oxygen vacancy and carbonates compared with the as-prepared sample.

Jointing of Coated Conductors by Using Nano-particle Metal Pastes

Development of a jointing technique of coated conductors is important for all applications, such as superconducting magnets, cables, etc. Low resistance jointing techniques by means of silver diffusion [1] and for superconducting joints[2] have been reported so far. Since these processes were carried out at higher temperatures than the O2 annealing temperature for appropriate carrier doping to the REBa2Cu3O7-d (REBCO) crystals and resulted in oxygen deficiency in the REBCO crystals, long time O2 annealing was required for compensation of this oxygen deficiency. Because the long time and high temperature post annealing is an inappropriate process as on-site technology, solder jointing technology has been widely accepted, in general, for practical applications. However, the resistance of the solder joint is 50 - 100 nΩ, and then the Joule heat generation in the joint region is a serious problem and must be solved. Consequently, we have studied a new jointing technique by using the pastes containing of silver or gold nano-particles. Because the Ic value of GdBCO was deteriorated with higher temperature heat treatment, we have tried to develop a jointing technology with the low temperature (below 200°C). We used the nano-particle metal pastes (∼5nm) which contained dispersants around the chemically active surface of nano-particles and dissociates at low temperatures and achieved the low resistance joint (∼ 3nΩ, 10 x 160mm2, 77K) as well as no Ic degradation without O2 post annealing.

AlGaN/GaN MOS-HEMTs-on-Si employing sputtered TaN-based electrodes and HfO2 gate insulator

We report on a low specific on-resistance (Ron,sp) of 3.58mΩ-cm2 and a high breakdown voltage of 1.4kV in a CMOS-compatible AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistor (MOS-HEMT). The MOS-HEMT is on a Si substrate and uses TaN electrodes and a HfO2-gate insulator. The sputtered TaN – a substitute for Au that has low resistivity, high work function, and thermal stability – was applied at room temperature to the gate, source, and drain. In order to obtain a low Ron,sp and high breakdown voltage, sputtering power and post-annealing temperature were optimized by measuring the characteristics of TaN. Using optimized conditions, a sputtering power of 50W, and an annealing temperature of 880°C, we successfully achieved a high on/off current ratio of 6×109 for the proposed AlGaN/GaN MOS-HEMT at a gate–drain distance of 10μm. These results indicate that the TaN process is a promising technique for power-switching GaN devices with CMOS compatibility.

Electrical properties of SiGe nanowire following fluorine/nitrogen plasma treatment

The improvements to electrical properties of SiGe nanowires by surface plasma treatment were investigated. Various durations of pre-oxidation with fluorine; ambients for post-nitridation plasma treatment, and annealing temperature after plasma treatment, 800–950°C, were applied. Pre-oxidation treatment using fluorine plasma; improved the conductance of SiGe nanowires because the Si–F binding energy created a more stable interface state than bare nanowire on the surface of SiGe. N2 plasma incorporated more N than does in NH3 plasma, and NH3 has the drawback of introducing electron traps, causing Si–H bonds to break in the subsequent annealing process. Since the reparation of surface defects by plasma treatment is valid, the high post-annealing temperature to reduce defect by re-crystallizing can be reduced. Hence, Ge diffusion at low post-annealing temperature did not reduce the high concentration of Ge at the SiGe nanowire surfaces.

The reason of degradation in electrical properties of ZnO:Al thin films annealed with various post-annealing temperature

ZnO:Al (AZO) thin films were deposited on glass substrates by RF magnetron sputtering at room temperature and post-annealed in rapid thermal annealing (RTA) system. The effect of post-annealing temperature on the structural, optical, and electrical properties was investigated. As the post-annealing temperature increased, electrical conductivity is deteriorated due to a decrease in the mobility or carrier concentration, gradually. According to X-ray photoelectron spectroscopy (XPS) analysis, the behavior of mobility and carrier concentration is attributed to increase the O2 absorption on film surface, which act as rising the barrier potential at the low post-annealing temperature (200 °C) and reducing the density of donor-like defects at the high post-annealing temperature (400 °C). In case of post-annealing, the minimization of O2 absorption is a very important factor to obtain better electrical properties.

Low-temperature fabrication (

This paper presents a low temperature fabrication of amorphous IGZO TFTs (a-IGZO TFTs) via high density CVD and superimposed rf/dc magnetron sputtering below 150 °C Low temperature processed SiOx films were been prepared in high density plasma chemical vapor deposition with inductively-coupled plasma (ICP) source and their electrical properties of these films have been investigated as a function of an ICP power and an O2 flow rate. Also, we found that a-IGZO semiconductor could be affected by a dc self-bias of a target surface using a superimposed rf/dc magnetron sputtering. Increasing a dc self-bias, higher post-annealing temperature is needed to achieve their electrical characteristics of a-IGZO TFTs. For a low-temperature and high performance a-IGZO TFTs, therefore, it is necessarily considered that a-IGZO semiconductors could be damaged due to accelerated negative oxygen ions during conventional magnetron sputtering.

The induction of a graphite-like phase on diamond films by a Fe-coating/post-annealing process to improve their electron field emission properties

The electron field emission (EFE) process for diamond films was tremendously enhanced by Fe-coating and post-annealing processes. Microstructural analysis indicates that the mechanism for the improvement in the EFE process is the formation of nanographites with good crystallinity that surround the Fe (or Fe3C) nanoclusters. Presumably the nanographites were formed via the reaction of Fe clusters with diamond films, viz. by the dissolution of carbons into Fe (or Fe3C) clusters and the reprecipitation of carbon species to the surface of the clusters, a process similar to the growth of carbon nanotubes via Fe clusters as catalyst. Not only is a sufficiently high post-annealing temperature (900°C) required but also a highly active reducing atmosphere (NH3) is needed to give a proper microstructure for enhancing the EFE process. The best EFE properties are obtained by post-annealing the Fe-coated diamond films at 900°C in an NH3 environment for 5 min. The EFE behavior of the films can be turned on at E0 = 1.9 V/μm, attaining a large EFE current density of 315 μA/cm2 at an applied field of 8.8 V/μm (extrapolation using the Fowler–Nordheim model leads to Je = 40.7 mA/cm2 at a 20 V/μm applied field).

Synthesis of CaIn2O4 Rods and Its Photocatalytic Performance Under Visible-light Irradiation

A type of CaIn2O4 particle was synthesized at a relatively low temperature by a solution-combustion method using calcium nitrate and indium nitrate as oxidizers and glycine as a fuel, followed by a high-temperature postannealing, during which the nanometric grains of the as-combusted CaIn2O4 powder self-assembled into nano-capsules, and subsequently the nano-capsules linked end to end to form the regular CaIn2O4 rods with the diameter of 300 nm and the length of about 2 μm. The CaIn2O4 rods showed significantly higher photocatalytic activity for methylene blue degradation and toluene oxidation under visible-light irradiation than that of the sample synthesized by the conventional solid-state reaction. Particularly, the Pt-dispersed CaIn2O4 rods exhibited excellent photocatalytic activity for water decomposition under visible-light irradiation. The high crystallization degree, low impurity level and relatively large surface area of CaIn2O4 rods were considered as the important factors for its high photocatalytic performance.

Raman spectroscopic characterization of the microstructure of V2O5 films

The vanadium pentoxide (V2O5) films were deposited on silicon wafer by DC magnetron sputtering. By Raman scattering measurements, the microstructure properties of the V2O5 films prepared with different O2–Ar gas flow ratios and annealed at different temperatures were studied, respectively. The results revealed that the increase of O2–Ar gas flow ratio during sputtering was of advantage to prepare the V2O5 film with desired layer structure. A high post-annealing temperature (below 500 °C) induced the crystallization and the formation of the integrated structure of V2O5 film. However, it was found that both intensities of Raman scattering peaks at 146 cm−1 and 994 cm−1, respectively, decreased for samples annealed at a temperature of 550 °C. The peak at 146 cm−1 was attributed to skeleton bent vibration and that at 994 cm−1 was due to the stretching vibration of vanadyl V=OA bond. It showed that the high-temperature annealing was believed to have distorted the microstructure of V2O5 films. The oxygen vacancies were, therefore, induced, which benefited the formation of V-OA-V bonds between layers. The result of X-ray diffraction measurements was in good agreement with that of Raman scattering spectra.

Enhanced Tc of Bi(Pb)2223 sintered bulks up to 115 K

Enhancement of Tc was attempted for Bi(Pb)2223 sintered bulks by optimizations of starting cation composition and post-annealing conditions. Tc was enhanced from 110.4 K to 111.4 K after post-annealing at ~700°C in 1%O2. Additional high temperature annealing at ~830°C in air largely improved crystallinity of Bi(Pb)2223 and high Tc up to 114.3 K was achieved. Increases in the c-axis length indicated that the enhancement of Tc is possibly due to changes in cation composition towards the stoichiometric one. An as-synthesized Bi(Pb)2223 bulks starting from Sr-rich compositions showed slightly high Tc of 110.8 K, suggesting suppression of partial substitution of Ca and/or Bi for the Sr-site. In addition, Bi-rich starting composition resulted in decreases of secondary phases without suppression of Tc. High temperature post annealing in air performed for these Sr-rich or Bi-rich bulks also improved Tc's up to 114.4 and 114.8 K, respectively.