Annealing In Oxygen Atmosphere Research Articles

Conductance modification of molybdenum oxide thin films through oxygen-vacancy engineering for visible-blind ultraviolet photodetection

We propose a simple approach to locally modify the conductance of molybdenum oxide thin films with thermal annealing in oxygen atmosphere at relatively low temperature for constructing a visible-blind ultraviolet photoconductor. The amorphous MoO x is grown by remote plasma enhanced atomic layer deposition (RPALD), and then crystallized into α-MoO x at 500 °C in argon atmosphere, which exhibits good conductance with resistivity of 3.9 × 10−3 Ω cm due to the formation of oxygen vacancies. Good ohmic contact between Ti and the crystallized MoO x is demonstrated with specific contact resistance of 9.74 × 10−4 Ω cm2. The lateral Au/Ti-MoO x -Ti/Au structures are defined and the conductance of the exposed MoO x channel is significantly modified by thermal annealing in oxygen atmosphere to form a photodetector, which shows obvious photoresponse at the wavelength of less than 372 nm with low dark current of 0.9 pA at 5 V, and the remarkable responsivity of 0.75 mA W−1 at 280 nm is achieved with a high ultravoilet/visible rejection ratio. The low dark current and incredible responsivity can be attributed to the good ohmic contacts of untreated MoO x and the reduction of number of oxygen vacancies in the MoO x channel. The key role of oxygen vacancy on the conductance of MoO x has been demonstrated. Those results suggest that the MoO x thin films are promising candidate for visible-blind ultraviolet photodetectors in a simple complementary metal oxide semiconductor (CMOS)-compatible process.

Epitaxial Growth of Cobalt Oxide Thin Films on Sapphire Substrates Using Atmospheric Pressure Mist Chemical Vapor Deposition

This study demonstrated the epitaxial growth of single-phase (111) CoO and (111) Co3O4 thin films on a-plane sapphire substrates using an atmospheric pressure mist chemical vapor deposition (mist-CVD) process. The phase structure of the grown cobalt oxide films was manipulated by controlling the growth temperature and process ambient, confirmed through X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. Furthermore, the electrical properties of Co3O4 films were significantly improved after thermal annealing in oxygen ambient, exhibiting a stable p-type conductivity with an electrical resistivity of 8.35 Ohm cm and a carrier concentration of 4.19 × 1016 cm−3. While annealing CoO in oxygen atmosphere, the Co3O4 films were found to be most readily formed on the CoO surface due to the oxidation reaction. The orientation of the atomic arrangement of formed Co3O4 was epitaxially constrained by the underlying CoO epitaxial layer. The oxidation of CoO to Co3O4 was largely driven by outward diffusion of cobalt cations, resulting in the formation of pores in the interior of formed Co3O4 films.

Atmosphere and cooling rate effect on the dielectric behavior of the lead-free piezoelectric Bi1/2K1/2TiO3

The electromechanical behavior and phase transition of lead-free piezoelectric Bi1/2K1/2TiO3 (BKT) can be modified without changing the processing parameters, composition, or microstructure through post-densification thermal treatment. Although this provides a method to control the disorder and, thereby, the thermal stability, the role of annealing atmosphere remains not well understood. In this work, solid-state processed BKT was annealed with varying cooling rates (5 K/min to 0.1 K/min) and atmospheres (air, oxygen, nitrogen) in order to investigate influence on the functional properties. Crystal structure analysis revealed an enhanced evaporation of volatile constituents of BKT ceramics, namely Bi3+ and K+ after the annealing in oxygen atmosphere, leading to decreasing properties, i.e., dielectric response. Also, a suppression of the relaxor-to-ferroelectric transition is observed in the dielectric response at lower cooling rates, demonstrating the influence of the atmosphere and cooling rate during thermal process in BKT. The findings are linked to structural changes respectively defect content (A-sites vacancies) and chemical homogeneity of A-site cations in BKT atmospherically annealed samples.

Experimental and Theoretical Investigation of the Surface Electronic Structure of ZnGa2O4(100) Single‐Crystals

Herein, a detailed experimental and theoretical investigation on the surface electronic structure of ZnGa2O4(100) bulk single‐crystals, with a special emphasis on the surface preparation, is presented. The surface crystallizes in the bulk‐derived structure, even at low annealing temperatures. Thermal treatments in ultra‐high vacuum have detrimental effects, as they cannot remove the carbon contamination and induce substantial zinc losses, further exacerbated by sputtering. A short sputtering duration and annealing in oxygen atmosphere dramatically reduce the zinc and oxygen losses in the crystal surface, leading to a contamination‐free, crystalline surface of nearly stoichiometric composition. The investigation of the valence states along the high symmetry directions of the Brillouin zone compares favorably with ab initio pseudopotential calculations, indicating a good surface quality and overall agreement with theory. An in‐depth analysis of the measured and simulated valence band peak intensities reveals difficulties associated with the precise description of the metal‐oxygen hybridization. This study provides a first fundamental understanding of the electronic structure of ZnGa2O4, while also indicating that the surface thermal instability is a challenging task that should be taken into account for the fabrication of heterostructures based on ZnGa2O4.

Microwave and furnace annealing in oxygen ambient for performance enhancement of p-type SnO thin-film transistors

In this study, we investigated the effect of microwave-irradiation annealing (MWA) and thermal furnace annealing (FA) in oxygen ambient on the active channel layer of p-type tin-oxide (SnO) thin-film transistors. At very low source-drain voltage of −0.1 V, the MWA at 1200 W and FA at 300 °C samples have exhibited significant improvement in the electrical characteristics such as subthreshold swing (SS) of 0.93 and 0.485 V dec−1, the I on/I off ratio of 1.65 × 104 and 3.07 × 104, the field-effect mobility (μ FE) of 0.16 and 0.26 cm2 V−1 s and ultra-low off-state current of 1.9 and 2.0 pA respectively. The observed performance enhancement was mainly attributed to the reduction of interface trap density (N t) by tuning the power of MWA and optimizing the temperature in FA. From the result, we observed the optical band gap (E g) increased by 6% in FA, and 12% in MWA, which confirms improved crystallinity and reduction of defect states. Additionally, a low thermal budget microwave anneal process has shown high transmittance of more than 86% in the visible region (380–700 nm). The physical characterization indicates the partial phase transformation of SnO to SnO2 with retaining p-type conductivity in both annealing processes. The results demonstrate that both the annealing process could be highly promising to be used in the complementary logic circuits of new generation flexible/transparent displays.

Revival of Smooth MgO(100) Surface: Ar Ion‐Beam Milling and Postvacuum Annealing in Oxygen Atmosphere

A recreation procedure for achieving the smooth and clean surface morphology of the degraded MgO(100) substrates is presented. The surfaces of the degraded MgO(100) substrates are treated with Ar ion‐beam milling (IBM) and annealing in O2 atmosphere. After each treatment, the changes in the MgO(100) substrate surface morphology are characterized using X‐ray diffraction (XRD), a 3D optical profilometer, atomic force microscopy, and Fourier‐transform infrared (FTIR) spectroscopy and compared with a fresh MgO substrate. It is shown that before any treatment, XRD and FTIR spectra show peaks corresponding to hydroxyl and carbonate groups in the degraded samples, whereas after treatment, XRD and FTIR spectra are comparable with the fresh sample. Further, after treatment, the surface roughness Rav value for two used/degraded samples reduces from 129 and 186 nm to 3.96 and 7.91 nm, respectively, after combined Ar IBM and annealing treatment. It is shown that the surface quality of the treated MgO(100) substrate improves in comparison with as it was before any treatment and can be reused for the good quality thin‐film deposition.

Effect of annealing on HTS tapes with a cerium oxide layer inserted between the REBaCuO and silver layers

This paper presents extensive electrical, microstructural and chemical characterizations of HTS coated conductor samples in which an oxide layer (CeOx) has been added between the superconductor (GdBaCuO) and the silver (Ag) layers, in an attempt to increase the interfacial resistance between these two conductive layers. This increase of interfacial resistance is required to realize the current flow diverter (CFD) architecture in HTS tapes. All samples in this paper have been characterized before and after performing an annealing in oxygen atmosphere. The purpose of the annealing was to reduce the interfacial resistance generated by the CeOx layer, in order to achieve a proper value for the CFD architecture. Samples with different thicknesses of CeOx, namely 0, 10, 35 and 100 nm, have been produced and characterized. The critical current and the critical temperature have been measured to determine the quality of the superconducting layers, while cross-section transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) have been used to monitor the impact of the annealing. The results show a clear degradation of the superconducting layer for samples with a thick layer (≥35 nm) of CeOx after annealing at 450 °C. According to the EDS results, a reduction of the amount of barium is observed in the superconducting layer, which could explain the observed reduction of the critical current.

Effects of reoxidation on the dielectric and energy storage properties of Ce-doped (Ba,Sr)TiO3 ceramics prepared by hot-pressed sintering

Fully densified Ba0.6Sr0.34Ce0.04TiO3 ceramics with small grain microstructure (0.3−0.8 μm) and high insulation (∼1014Ω cm) could be successfully obtained by hot-pressed sintering (HPS) coupled with subsequent thermal annealing in oxygen atmosphere. The effects of annealing on the microstructure, dielectric, electric and energy storage properties were investigated with scanning electron microscope, X-ray photoelectron spectroscope, impedance and ferroelectric analyzers. The preferential oxidation of grain boundaries to gains resulted in the formation of electrically inhomogeneous microstructure, which could be much improved by increasing O2 pressure during annealing process. The reduction of Ti4+ in the as-sintered HPS sample could be decreased with increasing the annealing temperature up to 1200 °C in flowing O2 gas, leading to the decrease in dielectric relaxation and corresponding permittivity/loss above room temperature. Maximum energy density of 1.75 J/cm3 could be obtained under the field of 235 kV/cm with the efficiency of 85 %.

Dark current analysis of germanium-on-insulator vertical p-i-n photodetectors with varying threading dislocation density

Dark current characteristics of germanium (Ge) vertical p-i-n photodetectors were studied. Ge photodetectors were demonstrated on the germanium-on-insulator (GOI) platforms realized via direct wafer bonding and layer transfer. GOI platforms with two different threading dislocation densities (TDDs) of 3.2 × 106 cm−2 (low TDD) and 5.2 × 108 cm−2 (high TDD) were varied via furnace annealing in oxygen ambient. An ultra-low dark current density of 1.12 mA/cm2 for epi-Ge photodetectors was obtained for a low TDD Ge photodetector. This is reduced by a factor of 53 in comparison with a high TDD Ge photodetector. A dominant leakage contribution component shifts from bulk leakage to surface leakage as TDD decreases to 3.2 × 106 cm−2, suggesting that advanced surface passivation is required to further reduce the leakage current. Through an activation energy study, it is revealed that a primary bulk leakage mechanism shifts from Shockley–Read–Hall (SRH) leakage to diffusion leakage in a temperature range of 323–353 K. The surface leakage performed with plasma enhanced chemical vapor deposition-deposited SiO2 is governed by SRH and trap-assisted tunneling leakage processes. Two orders of magnitude enhancement in the effective carrier lifetime is observed with the reduction in TDD. This work suggests that bulk leakage current density and effective lifetime analysis provide a better understanding of TDD-dependent dark leakage current study.

Effect of thermal oxidation on the optical, electrical, and chemical properties of zinc nitride films grown by reactive magnetron sputtering

We have studied the effect of post growth annealing in oxygen ambient on the optical, chemical and electronic properties of zinc nitride thin films. The films were prepared by reactive radio frequency magnetron sputtering of zinc target in the presence of argon and nitrogen gasses at a substrate temperature of 300 °C. Post growth annealing was performed at annealing temperatures of 300, 400, 500, 600, and 700 °C in the oxygen environment to transform the zinc nitride films into p-type zinc oxide. Atomic force microscopy of the films reveal that surface roughness and grain size of the films are directly proportional to the post-growth annealing temperature. X-ray photoelectron spectroscopy of the films revealed that as-grown film has the highest intensity of nitrogen in the film whereas little nitrogen remains in the films that were annealed at 500 °C and higher temperatures. Films annealed at higher temperatures have lower carrier concentration but higher Hall mobility compared to the as-grown film and the films annealed at lower temperature. Moreover, as-grown film and the films annealed at lower temperature have n-type conductivity whereas films annealed at temperatures above 500 °C exhibit p-type conductivity. Films annealed at lower temperature have bandgap values closer to the zinc oxynitride but bandgap of the films annealed at higher temperatures have values close to the bandgap of zinc oxide. This indicates that post growth annealing of zinc nitride films at 500 °C in oxygen ambient transforms it into p-type zinc oxide.

Effect of Annealing on HTS Tapes with a Cerium Oxide Layer Inserted between the REBaCuO and Silver Layers

This paper presents extensive electrical, microstructural and chemical characterizations of HTS coated conductor samples in which an oxide layer (CeOx) has been added between the superconductor (GdBaCuO) and the silver (Ag) layers, in an attempt to increase the interfacial resistance between these two conductive layers. This increase of interfacial resistance is required to realize the current flow diverter (CFD) architecture in HTS tapes. All samples in this paper have been characterized before and after performing an annealing in oxygen atmosphere. The purpose of the annealing was to reduce the interfacial resistance generated by the CeOx layer, in order to achieve a proper value for the CFD architecture. Samples with different thicknesses of CeOx, namely 0, 10, 35 and 100 nm, have been produced and characterized. The critical current and the critical temperature have been measured to determine the quality of the superconducting layers, while cross-section transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) have been used to monitor the impact of the annealing. The results show a clear degradation of the superconducting layer for samples with a thick layer (≥ 35 nm) of CeOx after annealing at 450 oC. According to the EDS results, a reduction of the amount of barium is observed in the superconducting layer, which could explain the observed reduction of the critical current.

Enhanced ferromagnetism and conductivity in epitaxial LaMnO3 thin films by oxygen-atmosphere annealing

We have investigated the effect of the excess oxygen on the structural, magnetic, and transport properties in LaMnO3 thin films by post-annealing in the oxygen atmosphere. The ferromagnetism and conductivity of the LaMnO3 films are greatly enhanced after post-annealing. The valence states of Mn ions are trivalent in the as-grown film and become trivalent and tetravalent mixed in the annealed film. Jahn-Teller interaction is suppressed due to a reduction of MnO6 distortion, confirmed by Raman spectra. The conversion from Mn3+ to Mn4+ and suppression of the Jahn-Teller interaction are responsible for the enhancement of ferromagnetism and conductivity in annealed films.

Er implantation into various cuts of ZnO – experimental study and DFT modelling

This paper presents a DFT study of the positions of erbium ions in the ZnO structure as well as experimental study of Er ion implantation into different crystallographic cuts of ZnO. The theoretical simulations have compared cohesive energies and defect-formation energies for different Er positions in the wurtzite ZnO structure. In the experimental part, single-crystal ZnO substrates were implanted with Er+ ions at an energy of 190 keV using fluences of 1 × 1016 and 5 × 1016 ion.cm−2. The ion implantation was followed by the application of the thermal annealing in oxygen atmosphere at 1000 °C for 5 h. The RBS/channelling method with fine scans was used to study the positions of erbium ions and structure recovery during the annealing process. The Er-doped ZnO samples exhibited clear luminescence in the NIR spectral region at around 1.5 μm. This work provides new results on the comparison of erbium ion implantation into different polar and non-polar crystallographic cuts of ZnO, resulting in different luminescence properties of the samples. Experimental and theoretical results are compared as well.

Effect of post-deposition annealing in oxygen atmosphere on LiCoMnO4 thin films for 5 V lithium batteries

Thin-film batteries are a promising microscale high-capacity energy sources for future micro devices. One possible way to increase the energy density is to use a cathode made of spinel LiCoMnO4, which has a theoretical specific energy of 475 Wh/kg and operates at about 5 V. However, one problem of this material is the loss of oxygen in the lattice during the thin-film formation process, which causes the loss of capacity at 5 V and the appearance of unexpected peak at around 4 V. In the study reported here, the effect of oxygen loss on the thin-film battery performance was investigated using post-deposition annealing of the thin-films under an oxygen flow at different temperatures and for different periods of time. The crystallinity and oxygen deficiency were characterized by the intensity of the X-ray diffraction (XRD) peaks and their shift in position. A clear correlation was found between the discharge capacity and the XRD peak shift (or oxygen content of the thin films). Based on these results, the optimum combination of conditions for post-deposition annealing of the LiCoMnO4 thin films was determined to be a temperature of 600 °C for 6 h under an oxygen atmosphere.

Thermal annealing induced competition of oxidation and grain growth in nickel thin films

The interface of Ni-NiO thin films was developed by thermal evaporation of nickel and subsequent annealing in oxygen atmosphere at 400 °C at varying duration of time. The evolution of layer thicknesses with annealing time was studied using rutherford backscattering spectrometry. The structural characterization showed grain growth stagnation for Ni at higher duration of annealing. The Ni phase had more crystallinity compared to the NiO phase. The surface was studied using atomic force microscope. The magnetic domains were also imaged. Magnetic stripe domain patterns were observed for selected films. Variation in saturation magnetisation and coercivity with annealing time was observed. The observation of weak exchange bias shows the importance of antiferromagnetic phase in determining the exchange bias properties. Thermal annealing of Ni films caused a competition among oxidation and grain growth.

Submicrometer p-Type SnO Thin-Film Transistors Fabricated by Film Profile Engineering Method

We reported the fabrication of submicrometer p-type tin monoxide (SnO) thin-film transistors (TFTs) with a channel length of $0.2~\mu \text{m}$ for back-end-of-line applications using a film profile engineering (FPE) approach. Material analyses indicate that the as-deposited SnO films are amorphous, while be transformed to polycrystalline after a thermal annealing in oxygen ambient. Fabricated p-type SnO FPE-TFTs of a channel length of $0.2~\mu \text{m}$ were manifested with ON/OFF current ratio higher than 105 and subthreshold slope of 320 mV/decade, superior to the data of submicrometer SnO devices ever reported. The extracted field-effect mobility is about 0.25 ${\mathrm {cm}}^{\text {2}}/\text{V}\cdot \text{s}$ . After ruling out the influence of source/drain series resistance, the intrinsic field-effect mobility is found to be about 1 ${\mathrm {cm}}^{\text {2}}/\text{V}\cdot \text{s}$ .

Electroluminescence energy efficiency of Si-structures with different compound of nanoscale dislocation complexes

Changes in the defect structure and luminescence properties of silicon p-type crystals surface layer under the influence of plastic deformation and high temperature annealing in oxygen atmosphere were investigated. A special role of dislocations in the surface layer of silicon during the formation its energy spectrum and rebuilding the defective structure was established. It is shown that the concentration of linear defects more than 104 cm−2 enriched subsurface layer with electrically-active complexes (dislocation—oxygen, dislocation—vacancy, dislocation—interstitial atoms of silicon) that are effective radiative recombination centers. It has been demonstrated that mixed treatment of silicon crystals by plastic deformation, high temperature annealing in the flowing oxygen atmosphere and elastic deformation at the final stage increases the energy efficiency of the radiative structures.

Luminescence in the Visible Region from Annealed Thin ALD‐ZnO Films Implanted with Different Rare Earth Ions

Epitaxial ZnO thin films grown by atomic layer deposition on GaN/Al2O3 substrates are implanted with Yb, Dy, and Pr ions to a fluence of 5 × 1014 at cm−2 and subsequently anneals at 800 °C using a rapid thermal annealing (RTA) system. Structural properties of implanted and annealed ZnO films and the optical response are evaluated by channeling Rutherford backscattering (RBS/c) and photoluminescence spectroscopy (PL), respectively. RTA leads to a partial removal of the post‐implantation defects with simultaneous native defects transformation and optical activation of RE ions. It is found that two groups of defects: defects formed during implantation process and native defects, play an important role in the luminescence in the visible region. The room temperature PL spectra obtained from annealed ZnO:RE films do not show sharp PL lines from transitions within the RE 4f shell, but show near band gap emission and defect related emission, which energy emission is controlled by the RE atoms. It suggests a presence of RE‐related complexes that are formed during high‐temperature annealing in oxygen atmosphere. The excitonic and defect emission modified by RE ions create an optical response of the system resulting in a specific color of the emitted light.

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.

Improvement of the thermal stability of Nb:TiO2−x samples for uncooled infrared detectors

In order to reduce the sun-burn effect in a sample of the bolometric material Nb:TiO2−x, oxygen annealing was carried out. This effect can be examined by comparing thermal stability test results between the as-deposited and oxygen-atmosphere-annealed samples under high-temperature exposure conditions. Structural studies confirm the presence of amorphous and rutile phases in the as-deposited and annealed samples, respectively. Composition studies reveal the offset of oxygen vacancies in the Nb:TiO2−x samples through oxygen-atmosphere annealing. The oxygen atoms were diffused and seemed to occupy the vacant sites in the annealed samples. As a result, the annealed samples show better thermal stability performance than the as-deposited samples. The universal bolometric parameter (β) values were slightly decreased in the oxygen-annealed Nb:TiO2−x samples. Although bolometric performance was slightly decreased in the oxygen-annealed samples, high thermal stability would be the most essential factor in the case of special applications, such as the military and space industries. Finally, these results will be very useful for reducing the sun-burn effect in infrared detectors.