N2 Annealing Research Articles

Electrical and optical properties of wide-gap n-type Sn2Ta2O7 films

Wide-gap n-type Sn2Ta2O7 polycrystalline films were prepared by RF-magnetron sputtering followed by annealing in a reducing atmosphere (N2). Sn2Ta2O7 is known to show both p- and n-type conductivity. The electrical and optical properties of the films were examined as a function of annealing time. The bandgap of the film was estimated to be 2.7 or 3.2 eV assuming an indirect or direct transition, respectively. The electrical conductivity of the film at 300 K increased from 2.1 × 10−8 S cm−1 (as-deposited) to a maximum of 2.1 S cm−1 (annealed for 14 h). The temperature dependence of the conductivity changed from semiconducting to degenerate semiconducting behavior with increasing annealing time, suggesting that oxygen vacancies were generated by the annealing in N2. From the temperature dependence of the mobility, it was found that neutral impurities were the dominant scattering centers for electron carriers.

Influences of annealing atmosphere on phase transition temperature, optical properties and photocatalytic activities of TiO2 phase-junction microspheres

TiO2 microspheres were successfully fabricated and subsequently annealed in air and N2 atmosphere under different temperatures. The morphologies, phase transition temperatures, optical properties were investigated by SEM, XRD, PL and XPS. The photocatalytic performances of these products were also evaluated toward Rhodamine B (RhB) degradation. The experimental data implied that the anatase phase could gradually transform to rutile phase with the temperature increasing from 450 °C to 600 °C under air atmosphere. However, the phase transition was inhabited to the range of 500–650 °C under N2 atmosphere. Analysis showed that the synergistic effect of the phase-junction could separate photo-generated electron-hole pairs to improve the photocatalytic activities. Moreover, N2 annealing could bring about the formation of charged oxygen vacancies and Ti3+, which further prolonged the life time of charge carriers and optimized the photocatalytic performance.

SiC nanodot formation in amorphous-Si and poly-Si substrates using a hot-C+-ion implantation technique

We experimentally studied SiC nanodot formation in an amorphous-Si (a-Si) and poly-Si on quartz substrates, using a hot-C+-ion implantation technique and post-N2 annealing, compared with SiC-dots in a (100) crystal-Si (c-Si) on insulator substrate. Even in the poor crystal quality substrates of the C+-ion implanted in a-Si and poly-Si layers, we experimentally verified 3C-SiC dot formation by transmission electron microscopy, and the strong photoluminescence (PL) intensity in the near-UV-vis regions, because a-Si is partially poly-crystallized by the high-temperature processes of hot-C+-ion implantation and post-N2 annealing. The PL spectral line shape strongly depends on the Si crystal structures, but the peak PL intensity after N2 annealing is almost independent of the Si crystal structures. Moreover, the PL spectrum can be explained by the sum of PL emissions from different cubic and hexagonal polytypes of SiC. We clarified that the three Si crystal structures have a different contribution ratio of PL components of SiC polytypes.

Hierarchical Microboxes Constructed by SnS Nanoplates Coated with Nitrogen-Doped Carbon for Efficient Sodium Storage.

The design and synthesis of hierarchical microboxes, assembled from SnS nanoplates coated with nitrogen-doped carbon (NC) as an anode material for sodium-ion batteries, is demonstrated. The template-engaged multistep synthesis of the SnS@NC microboxes involves sequential phase transformation, polydopamine coating, and thermal annealing in N2 . The SnS@NC composite with two-dimensional nano-sized subunits rationally integrates several advantages including shortening the diffusion path of electrons/Na+ ions, improving electric conductivity, and alleviating volume variation of the electrode material. As a result, the SnS@NC microboxes show efficient sodium storage performance with high capacity, good cycling stability, and excellent rate capability.

Hierarchical Microboxes Constructed by SnS Nanoplates Coated with Nitrogen‐Doped Carbon for Efficient Sodium Storage

AbstractThe design and synthesis of hierarchical microboxes, assembled from SnS nanoplates coated with nitrogen‐doped carbon (NC) as an anode material for sodium‐ion batteries, is demonstrated. The template‐engaged multistep synthesis of the SnS@NC microboxes involves sequential phase transformation, polydopamine coating, and thermal annealing in N2. The SnS@NC composite with two‐dimensional nano‐sized subunits rationally integrates several advantages including shortening the diffusion path of electrons/Na+ ions, improving electric conductivity, and alleviating volume variation of the electrode material. As a result, the SnS@NC microboxes show efficient sodium storage performance with high capacity, good cycling stability, and excellent rate capability.

On the origin of enhanced resistive switching behaviors of Ti-doped HfO2 film with nitrogen annealing atmosphere

In this work, the resistive switching (RS) characteristics of Ti-doped HfO2 under different doping concentration and annealing condition were theoretically investigated by using the first-principles calculation method. For a 2 × 2 × 2 HfO2 supercell, the formation energy of an oxygen vacancy (Vo) reaches the minimum when three Hf atoms were substituted by three Ti atoms. Based on the 3‑Ti-doped HfO2 supercell model, numerical results show that low oxygen partial pressure, high annealing temperature and N2 annealing atmosphere would lead to a low Vo formation energy. By calculating the migration energy of a Vo, we found that the Vo tends to migrate near and towards the Ti dopants. The concentration of Vo and N2 annealing atmosphere are also beneficial for the connection of conducting filaments. Our numerical results show reasonable agreement with previous experiment about the RS performance of ITO/Ti:HfO2/Pt device.

Formation of non-alloyed Ti/Al/Ni/Au low-resistance ohmic contacts on reactively ion-etched n-type GaN by surface treatment for GaN light-emitting diodes applications

Ti/Al/Ni/Au (30/120/20/100 nm) non-alloyed ohmic contacts on reactively ion-etched n-GaN have been obtained by thermal annealing in N2 + O2 ambient prior to metal contacts deposition. After surface treatment, contacts show the linear current–voltage (I–V) characteristics with specific contact resistance (SCR) of 2.91 × 10−5 Ω-cm2 without any post-deposition annealing, whereas, SCR of untreated sample has been found 1.02 × 10−4 Ω-cm2. The improvement in SCR of Ti/Al/Ni/Au contacts with this process may be attributed to formation of n+-highly doped layer due to presence of oxygen during thermal annealing. A further increase in SCR of non-treated sample from 1.02 × 10−4 Ω-cm2 to 3.54 × 10−4 Ω-cm2, has been observed on further annealing of contacts at 550 °C in N2 + O2 ambient for 5 min, which is generally an essential condition for formation of low-resistance highly transparent p-contact on p-GaN during fabrication of conventional GaN light-emitting diodes (LEDs). Based on X-ray photoelectron spectroscopy results, we found that there is increase in Ga 3d photoelectron binding energy with this surface treatment, which indicates a shift of Fermi level closure to conduction band, resulting in decrease of Schottky barrier height (SBH). The reduction in SBH is responsible for formation of low-resistance Ohmic contacts on n-GaN. Such non-alloyed n-contacts formed on thermally annealed reactively etched n-GaN surface may open for fabrication of more efficient conventional GaN LEDs. In addition, the forward voltage of GaN LED fabricated by present suggested process lowered by an amount of 0.37 V at 100 mA compared to standard process.

Efficiency improvement of PERC solar cell using an aluminum oxide passivation layer prepared via spatial atomic layer deposition and post-annealing

In this study, Al2O3 thin films are deposited on p-type silicon using spatial atomic layer deposition with trimethylaluminum and H2O. The films are annealed in atmosphere (ATM), forming gas (FG) and nitrogen (N2) at temperatures of 300–750 °C. Effects of annealing gas ambient and temperature on structural, electrical, and passivation properties of Al2O3/Si are systematically investigated. The experimental results show that the ATM annealing leads to an interfacial silicon oxide more than two times thicker than that of the samples annealed in FG and N2. The ratio of tetrahedral AlO4 to octahedral AlO6 can be correlated to the negative fixed oxide charge density (Qf) near the interface of Al2O3/Si. The 600 °C ATM-annealed sample has the highest Qf of 3.23 × 1012 cm−1 and thus gives the best field effect passivation. The sample annealed in FG at 450 °C has the lowest interface trap density (Dit) of 3.98 × 1011 eV−1 cm−2, indicating that the hydrogen is more effective than oxygen for chemical passivation. Overall, the FG-annealed sample has the highest lifetime of 933.8 μs, showing that chemical passivation is the primary consideration. The ATM annealing requires higher temperatures (~600 °C) to reach the optimal passivation, whereas the FG and N2 annealing temperature is limited to 450 °C to avoid dehydrogenation. Finally, for passivated emitter and rear contact cell fabrication, the cell with FG annealing has the best conversion efficiency of 21.43%, which is 0.17 and 0.54 percentage point higher than that of the cells with ATM and N2 annealing, respectively.

Co/Zn bimetallic oxides derived from metal organic frameworks for high performance electrochemical energy storage

Partial isomorphic substitution of Zinc in a two-dimensional Cobalt-based (Co-based) bimetallic Metal Organic Frameworks (MOFs) has been successfully synthesised on carbon cloth. Specifically, the Zn content corresponding to the Co to Zn ratio of 2:1 has been incorporated into the Co-based framework during the growth process. Cobalt-based bimetallic oxides ZnCo2O4 are then derived: one from the Bimetal Organic Frameworks via oxidation in air, and the other by first annealing in N2 for stabilisation before oxidation. Systematic characterisation results, including those using XRD, SEM, EDS, TEM and XPS, support the effective incorporation of Zn into the Metal Organic Frameworks. The nanocrystalline bimetallic oxides derived from MOFs exhibit flake-like morphology, the size and thickness of which are affected by Zn addition. Electrochemical performance of the MOF-derived nanocrystalline bimetallic oxides assembled on carbon cloth was examined in a KOH electrolyte (3 M) as the electrolyte at room temperature. The bimetallic oxides show an improvement in specific capacity by more than 300% over that of MOF-derived Co3O4 when used as an electrode material in supercapacitors, together with much improved stability. The capacity loss is reduced from 30.0% to less than 5.2% after 2000 charge–discharge cycles. This work illustrated the potential of bimetallic oxide structures derived from MOFs in delivering high supercapacitor performance.

Comprehensive investigation of the interfacial charges and dipole in GeOx/Al2O3 gate stacks of Ge MOS capacitor by postdeposition annealing

Postdeposition annealing (PDA) in N2, O2, NH3, and H2 is employed to explore the modulation of the interfacial charges and dipole in GeOx/Al2O3 gate stacks of a Ge MOS capacitor. We find that the properties of both the Ge/GeOx and GeOx/Al2O3 interfaces can be significantly tuned after PDA. Three types of charges exist in the Ge gate stacks: (i) the interfacial charges at the Ge/GeOx interface (Q1), (ii) the interfacial charges at the GeOx/Al2O3 interface (Q2), and (iii) the electric dipole at the GeOx/Al2O3 interface. After PDA, interfacial charge and dipole densities can be effectively tuned in different ambients. In particular, the PDA in the O2 and NH3 ambients is more distinguished to decrease the interfacial charges at the Ge/GeOx and GeOx/Al2O3 interfaces. In addition, dipole polarity can be modulated by annealing. Furthermore, we comprehensively analyze the operative mechanism to explain the charge distribution changes after PDA in various ambients. This work can be effectively applied to enhance the performance of Ge-based devices.

Low-resistance orthorhombic MoO3-x thin film derived by two-step annealing

Layer structured orthorhombic MoO3-x (α-MoO3-x) thin film with low resistivity of about 5 Ω⋅cm was obtained on glass substrate via conducting a two-step annealing treatment on the thin film deposited by thermal evaporation method. The first step annealing in air enables the formation of α-phase and layered structure, while the second step annealing in N2 gives rise to low resistivity without deteriorating crystal structure. Finally, this two-step annealing treatment empowers the formation of α-MoO3-x thin film on indium tin oxide (ITO) substrate, providing layer structured α-MoO3-x/ITO bilayer electrode for organic light emitting diode and thin film solar cells.

Tuning of optical bandgap, conductivity parameters, and PL emissions of SnO2:Ni thin films under Ar, N2, and O2 annealing

The influence of annealing atmosphere (N2, Ar, and O2) on optical properties and electrical parameters of SnO2:Ni thin films prepared by sol–gel process was investigated. The XRD results showed that the samples possessed tetragonal rutile-type phase, as well as Ni-doped SnO2 thin film under N2 annealing ambience revealed no distinct peaks. The FESEM images revealed that the film surface is constituted by homogenous spherical nanograins. The transmittance spectra of the films showed that O2 annealing enhanced the transparency of the films. The optical measurements yielded that annealing under oxygen led to the lowest extinction coefficient while annealing in Ar caused to the highest refractive index of SnO2:Ni thin films. The film annealed in O2 has the highest band-gap value, whereas Ar annealing reduced the band-gap value. The PL spectra disclosed an intense blue emission in N2 ambience. The Hall effect measurements indicated that the best electrical response (conductivity, carrier concentration, and mobility) in prepared samples is reached after annealing in Ar ambience. In addition, annealing in the O2 atmosphere converted the conductivity type of Ni-doped SnO2 thin films from n-type to p-type.

N–H-related deep-level defects in dilute nitride semiconductor GaInNAs for four-junction solar cells

Deep-level defects were investigated and compared among three molecular beam epitaxy (MBE)-grown dilute nitride semiconductor GaInNAsSb solar cells, one of which was as-grown and the other two were annealed in a metal organic chemical vapor deposition (MOCVD) atmosphere (H2 and AsH3) or a nitrogen (N2) atmosphere. A residual defect in the as-grown sample was firstly discovered and considered to be mainly responsible for the degradation in GaInNAsSb solar cells. Meanwhile, an N–H-related defect was confirmed, as well as the effects on background carrier concentration (BGCC) together with hydrogen incorporation. The N2 annealing showed a significant effectiveness of suppressing the defects and improving the solar cell properties.

Charge Trapping in Al2O3/$\beta$ -Ga2O3-Based MOS Capacitors

Trapping characteristics of MOS structures with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula> -Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> substrates and Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> gate dielectrics are evaluated via constant-voltage stress and X-ray irradiation. Traps that affect bias-induced charging are located primarily in the Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> dielectric layer, and are distributed broadly in time and/or energy. Stress-induced flatband voltage shifts are reduced by N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> annealing. Trap-assisted tunneling is shown to be responsible for the observed gate leakage. Hole trapping in the Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> dielectric layer dominates device radiation response. The relatively modest radiation-induced charge trapping observed in these devices is promising for the potential future use of Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> / <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula> -Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> devices in a space environment.

Novel Gate Insulator Process by Nitrogen Annealing for Si-Face SiC MOSFET with High-Mobility and High-Reliability

The gate insulator process for SiC-MOSFET was examined and high-quality interface was realized by employing the pre-annealing process before high-temperature N2 annealing. The pre-annealing evidently activated the interface to introduce nitrogen, and then field-effect mobility exceeded 50 cm2/Vs. The fabricated sample also demonstrated superior bias temperature instability (BTI) and excellent breakdown electric field of 11.7 MV/cm.

Effect of post deposition annealing and post metallization annealing on electrical and structural characteristics of Pd/Al2O3/6H-SiC MIS capacitors

PurposeAl2O3 used as gate dielectric enables exploitation of higher electric field capacity of SiC, improving capacitive coupling and memory retention in flash memories. Passivation of traps at interface and in bulk which causes serious threat is necessary for better performance. The purpose of this paper is to investigate the effect of post-deposition rapid thermal annealing (PDA) and post-metallization annealing (PMA) on the structural and electrical characteristics of Pd/Al2O3/6H-SiC capacitors.Design/methodology/approachAl2O3 film is deposited by ALD; PDA is performed by rapid thermal annealing (RTA) in N2 at 900°C for 1 min and PMA in forming gas for 10 and 40 min. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements data are studied in addition to capacitance-voltage (C-V) and current-voltage (I-V) characteristics for the fabricated Pd/Al2O3/SiC capacitors. Conduction mechanism contributing to the gate leakage current is extracted for the entire range of gate electric field.FindingsRTA forms aluminum silicide at the interface causing an increase in the density of the interface states and gate leakage current for devices with an annealed film, when compared with an as-deposited film. One order improvement in leakage current has been observed for the devices with RTA, after subjecting to PMA for 40 min, compared with those devices for which PMA was carried out for 10 min. Whereas, no improvement in leakage current has been observed for the devices on as-deposited film, even after subjecting to PMA for 40 min. Conduction mechanisms contributing to gate leakage current are extracted for the investigated Al2O3/SiC capacitors and are found to be trapfilled limit process at low-field regions; trapassisted tunneling in the mid-field regions and Fowler–Nordheim (FN) tunneling are dominating in high-field regions.Originality/valueThe effect of PDA and PMA on the structural and electrical characteristics of Pd/Al2O3/SiC capacitors suitable for flash memory applications is investigated in this paper.

Effect of oxygen treatment on structure and electrical properties of Mn-doped Ca0.6Sr0.4TiO3 ceramics

Different oxygen treatment methods, including O2 and N2 annealing, were conducted on Ca0.6Sr0.4TiO3 (CST) ceramics with varying Mn content (0 mol%, 0.5 mol% and 2.0 mol%). Structure characterization, including XRD and SEM, indicated the minimal effect of annealing on the microstructure. Grain boundaries were found to be sensitive to oxygen treatments, and annealing in O2 resulted in increased grain boundary resistance, while in N2 led to the opposite result. The insulating properties of bulk ceramics were found to be dominated by grain boundaries. Both the concentration and mobility of oxygen vacancies were confirmed to affect the energy storage properties to some extent in this work.

Effect of annealing atmosphere on the structure and dielectric properties of unfilled tungsten bronze ceramics Ba4PrFe0.5Nb9.5O30

Unfilled tungsten bronze ceramics with the nominal formula Ba4PrFe0.5Nb9.5O30 were synthesized via the standard solid-state sintering route, and the effects of oxygen vacancies on the dielectric and electrical properties were investigated in addition to the structure. Room-temperature X-ray diffraction showed that the N2-annealed sample had the largest cell volume. Low-temperature spectrum showed that N2 annealing rendered the dielectric constant and dielectric loss more frequency dispersive, whereas O2 annealing inhibited the frequency dispersion. The dc conductivity of all the samples originated from the electrons produced in the second ionization of oxygen vacancies and was most likely controlled by a mixed conduction mechanism of the electron and oxygen-vacancy ions. The N2-annealed sample has the highest dc conductivity owing to its high concentration of oxygen vacancies. The broadening of the Raman lines and the decrease of Raman intensity for the N2-annealed sample originated from a significant structural disorder. X-ray photoelectron spectra demonstrated that the increased oxygen vacancies caused by the change of valences of Fe and Pr ions contributed to the structural disorder.

Influence of N2 annealing on TiO2 tubes structure and its photocatalytic activity

In this work, the TiO2 tubes (TBs) were prepared by solvothermal method. The morphology and phase structure of TiO2 TBs is significantly affected by N2 annealing temperature. XRD was used to characterize the phase structure of the as-prepared samples. The morphology and surface areas were characterized by SEM and N2 adsorption–desorption, which show that the tubes were assembled with about 100-nm nanosheets and small ball particles under 400 and 600 °C N2 annealing; when temperature reached 800 °C, the surface of tubes appeared a lot of collapse and many large holes. In addition, the surface areas of 400 °C TiO2, 600 °C TiO2, and 800 °C TiO2 TBs were significantly affected by N2 annealing. Most importantly, the UV-vis and electrochemical tests demonstrate 600 °C TiO2 TBs exhibit higher absorption intensity and photocurrent; thus, it possess on better photocatalytic activity. Therefore, the photocatalytic performance for TiO2 TBs is significantly co-affected by surface area and mix-phase.

Effects of post-deposition annealing on sputtered SiO2/4H-SiC metal-oxide-semiconductor

Reactive sputtering followed by N2, NH3, O2, and NO post-deposition annealing (PDA) of SiO2 on 4H-SiC was investigated in this study. The results of ellipsometry, an etching test, and X-ray photoemission spectroscopy showed that N2 and NH3 PDA nitrified the SiO2. Devices using N2 and NH3 PDA exhibited a high gate leakage current and low breakdown field due to oxygen vacancies and incomplete oxynitride. SiO2/4H-SiC MOS capacitors were also fabricated and their electrical characteristics measured. The average breakdown fields of the devices using N2, NH3, O2, and NO PDA were 0.12, 0.17, 4.71 and 2.63 MV/cm, respectively. The shifts in the flat-band voltage after O2 and NO PDA were 0.95 and −2.56 V, respectively, compared with the theoretical value. The extracted effective oxide charge was −4.11 × 1011 cm−2 for O2 PDA and 1.11 × 1012 cm−2 for NO PDA. NO PDA for 2 h at 1200 °C shifted the capacitance–voltage curve in the negative direction. The oxygen containing PDA showed better electrical properties than non-oxygen PDA. The sputtering method described can be applied to 4H-SiC MOS fabrication.