Optimum Annealing Conditions Research Articles

High strength bulk Fe–Co alloys produced by powder metallurgy

Fe–Co alloys are extensively used in lamination form, but there are certain power generation applications that require Fe–Co rotors in bulk form. Experiencing only a dc magnetic field, these rotors can be as large as 0.5m in diameter, depending on the size of the generator. The forging of such large pieces of Fe–Co has proven to be difficult. The present study investigates powder metallurgy processing of a gas atomized FeCoNbV alloy through hot isostatic pressing (HIP) for manufacturing large size rotors with improved mechanical strength. Gas atomized FeCoNbV alloy powders with and without ball milling were hot isostatic pressed at temperatures between 675 and 850°C at a fixed pressure of 193MPa for up to 6h. Ball milling prior to HIP improved the yield strength. A further improvement in yield strength and in ductility was obtained after a disordering heat treatment at 730°C followed by a rapid quench to room temperature. The optimum HIP and annealing conditions resulted in samples with yield strengths of...

Optimum activation and diffusion with a combination of spike and flash annealing

Different shallow n-type and p-type dopants were annealed with spike, flash, and a combination of spike+flash or vice versa to find the optimum annealing condition for both activation and diffusion. The implant conditions investigated during this study were Ge+74 with B+11 as well as B+11, B49F2+, and As+75. The wafers were characterized regarding sheet resistance, junction depth, and chemical dose. An electrically active dose was derived from the Hall-effect measurement. Transmission electron microscopy analysis for the characterization of defects was done on selected samples. Boron implanted into crystalline as well as preamorphized silicon shows a similarly low sheet resistance which is independent of whether they are annealed with spike+flash, flash, or flash+spike. For arsenic by far the lowest sheet resistance is seen with a combination of spike+flash anneal. The main advantage when using a spike+flash anneal combination is that similar sheet resistance values for arsenic and boron implant can be achieved with the same anneal sequence.

Nickel-Aluminum Alloy Silicides with High Aluminum Content for Contact Resistance Reduction and Integration in n-Channel Field-Effect Transistors

In this paper, we demonstrate the silicidation of alloy film with the highest Al concentration reported to date for reduced contact resistance through process optimization. Successful formation of alloy silicide with the use of film that has an Al concentration as high as 51% is shown. The onset of agglomeration has been eliminated, and the silicide yields a electron barrier height, which is one of the lowest reported for any nickel alloy film. Subsequently, the benefits of the film using the optimal annealing condition are further verified through an 18% saturation drive current enhancement in n-channel metal-oxide-semiconductor field-effect transistors with silicide compared to NiSi. In addition, this paper also elucidates the dependency of alloy silicide properties on Al concentration and the annealing conditions.

Optimization of in situ annealing conditions for off-axis PLD MgB 2 films

We optimized the conditions for the in situ annealing that follows the off-axis pulsed laser deposition of MgB 2 thin films. The influence on the superconductivity of the two major annealing parameters, which are the dwell time, τ ann, and the sintering temperature, T ann, was investigated. The optimal annealing conditions regarding the transition temperature were obtained by analysing the change in the critical temperature, T c, with different dwell times and sintering temperatures. X-ray diffraction (XRD) θ–2 θ scans on the two series of films confirm the sole MgB 2 phase composition in the best T c film with a zero resistance T c of 34.2 K and transition width of 0.2 K. The film also shows good critical current density J c performance in magnetic fields.

Nanostructure of GaAs0.88Sb0.10N0.02/InP quantum wells grown by metalorganic chemical vapor deposition on InP

Abstract The effects of thermal annealing on the emission and microstructural characteristics of GaAs 0.88 Sb 0.10 N 0.02 /InP multiple quantum well (QW) structures were studied by photoluminescence (PL) spectroscopy and transmission electron microscopy (TEM). The results show that the optimum annealing conditions lead to improved PL intensity accompanied by only a small blue shift, contrasting the behavior of GaAsSbN /GaAs multiple QWs, and improved structural uniformity.

Formation and Characterization of 1.5-Monolayer Self-Assembled InAs/GaAs Quantum Dots Using Postgrowth Annealing

In this paper, we report that low-density InAs/GaAs quantum dots (QDs) can be formed by postgrowth annealing the samples with 1.5-monolayer (ML) InAs coverage, which is thinner than the critical layer thickness for the Stranski-Krastanov growth. The annealing procedure was performed immediately after the deposition of the InAs layer. The effects of annealing time and annealing temperature on the dot density, dot size, and optical characteristics of the QDs were investigated. The optimum annealing conditions to obtain low-density QDs are longer than 60 s and higher than 500degC . Meanwhile, no luminescence can be observed for the wetting-layer, which may suggest that the postgrowth annealing will make the wetting layer thinner and thus reduce the effects of wetting layer on carrier relaxation and recombination. On the other hand, we observe that a decrease of the PL intensity at the annealing conditions of 60 s and 515degC , which is possibly due to the increasing surface dislocations resulted from the In adatom desorption at higher annealing temperature.

Effects of Laser Processing Parameters on Grain Boundary Character Distribution and Corrosion Resistance of Austenite Stainless Steel

In order to modify grain boundary character distribution (GBCD) and to improve intergranualr corrosion (IGC) resistance of 304 stainless steel, laser surface remelting experiments were conducted on 304 stainless steel using a 2kW CW Nd: YAG laser, and the effects of laser processing parameters on GBCD and corrosion resistance were investigated in detail under the optimal annealing condition (1220K 28h). The experimental results showed that combination of laser surface remelting and the following annealing treatment could change the GBCD remarkably and improve the IGC resistance of 304 stainless steel. However, there are no obvious effects of laser processing parameters on the final depth of the processed zone, although the depth of the molten pool increases with the increase of the laser output power or the decrease of the scanning velocity, and the subsequent GBCD and corrosion resistance.

Characteristics of SiCN microstructures for harsh environment and high-power MEMS applications

This paper describes a novel processing technique for the fabrication of polymer-derived silicone carbonitride (SiCN) microstructures for extreme microelectromechanical system (MEMS) applications. A polydimethylsiloxane (PDMS) mold was formed on an SU-8 pattern using a standard UV photolithographic process. Next, the liquid precursor, polysilazane, was injected into the PDMS mold to fabricate free-standing SiCN microstructures. Finally, the solid polymer SiCN microstructure was crosslinked using hot isostatic pressure at 400°C and 205bar. The optimal pyrolysis and annealing conditions to form a ceramic microstructure capable of withstanding temperatures over 1400°C were determined. Using the optimal process conditions, the fabricated SiCN ceramic microstructure possessed excellent characteristics including shear strength (15.2N), insulation resistance (2.163×1014Ωcm), and BDV (1.2kV, minimum). Since the fabricated ceramic SiCN microstructure has improved electrical and physical characteristics compared to bulk Si wafers, it may be applied to harsh environments and high-power MEMS applications such as heat exchangers and combustion chambers.

Effect of laser annealing on crystallinity of the Si layers in Si/SiO 2 multiple quantum wells

We report on continuous-wave laser induced crystallisation processes occurring in Si/SiO 2 multiple quantum wells (MQW), prepared by remote plasma enhanced chemical vapour deposition of amorphous Si and SiO 2 layers on quartz substrates. The size and the volume fraction of the Si nanocrystals in the layers were estimated employing micro-Raman spectroscopy. It was found that several processes occur in the Si/SiO 2 MQW system upon laser treatment, i.e. amorphous to nanocrystalline conversion, Si oxidation and dissolution of the nanocrystals. The speed of these processes depends on laser power density and the wavelength, as well as on the thickness of Si-rich layers. At optimal laser annealing conditions, it was possible to achieve ∼100% crystallinity for 3, 5 and 10 nm thickness of deposited amorphous Si layers. Crystallization induced variation of the light absorption in the layers can explain the complicated process of Si nanocrystals formation during the laser treatment.

Effects of Postannealing on Orientation and Crystallinity of P-Type Transparent Conducting CuScO2 Thin Films

Highly c-axis-oriented CuScO2 thin films were successfully fabricated from polycrystalline CuScO2 thin films by pulsed laser deposition and followed by postannealing treatment. The oxygen pressure effects during postannealing on the surface morphology, and crystallographic and optical properties of the films were investigated. The growth orientation, crystallinity along both out-of-plane and in-plane directions, and surface morphology of the films were significantly improved by postannealing at an optimal oxygen pressure. Using a film postannealed under optimal annealing conditions, the optical and electrical properties of the film were measured. The optical average transmittance of the film was greater than 70% in the visible/near-infrared regions, and the energy gap for calculated direct allowed transition was 3.7 eV. The Hall coefficient measured using the van der Pauw electrode configuration was 1.9×10+1 cm3 C-1, indicating p-type conduction. The resistivity, carrier concentration, and Hall mobility of the film at room temperature were 9.9×10+1 Ω cm, 3.2×10+17 cm-3, and 2.0×10-1 cm2 V-1 s-1, respectively.

Elimination of Inclusions in (CdZn)Te Substrates by Post-grown Annealing

Post-grown annealing of (211) (CdZn)Te substrates has been used for elimination of Te and Cd inclusions with the objective of improving the yield of inclusion-free substrates for MBE growth of (HgCd)Te. Different annealing temperatures and Cd/Te overpressures were used to find the optimum annealing conditions. Te inclusions were significantly reduced by Cd-rich annealing at temperatures higher than 660°C, together with increasing the infrared transmittance at 10 µm to above 60%. Good crystalline quality was preserved after the annealing. Te-rich annealing at 700°C was found to be the optimum method for elimination of most of the Cd inclusions; infrared transmittance at 10 µm was suppressed by the annealing, however. Final Cd-rich annealing is recommended for infrared transmittance improvement.

TiO2 Nanocrystal Prepared by Atomic-Layer-Deposition System for Non-Volatile Memory Application

TiO2 nanocrystals were successfully fabricated using an atomic-layer-deposition (ALD) system. A TiN/Al2O3-laminated structure was employed as a starting structure, and after appropriate annealing, TiN was oxidized and TiO2 nanocrystals were formed. Experimental results indicate that rapid thermal annealing (RTA) temperature and annealing time are very critical factors. Also, the thickness of each TiN layer in the TiN/Al2O3-laminated starting structure is critical for TiO2 nanocrystal formation. Capacitance–voltage (C–V) measurement evidenced that an optimal annealing condition exists and an optimal annealing temperature and annealing time mainly depend on the thickness of each TiN layer in the TiN/Al2O3-laminated starting structure.

Structure-property relationships in the optimization of polysilicon thin films for electrical recording/stimulation of single neurons

We had earlier demonstrated the use of polysilicon microelectrodes for recording electrical activity from single neurons in vivo. Good machinability and compatibility with CMOS processing further make polysilicon an attractive interface material between biological environments on one hand and MEMS technology and digital circuits on the other hand. In this study, we focus on optimizing the polysilicon thin films for (a) electrical recording and (b) stimulation of single neurons by minimizing its electrochemical impedance spectra and maximizing its charge storage/injection capacity respectively. The structure-property relationships in ion-implanted (phosphorus) LPCVD polysilicon thin films under different annealing and doping conditions were carefully assessed during this optimization process. A 2D model of the polysilicon thin film consisting of 4 grains and 3 grain boundaries was constructed and the effect of grain size and grain boundaries on dc resistivity was simulated using device simulator ATLAS. Optimal processing conditions and doping concentrations resulted in a 10-fold decrease in electrochemical impedance from 1.1 kOmega to 0.1 kOmega at 1 kHz (area of polysilicon interface = 4.8 mm(2)). Subsequent characterizations showed that evolution of secondary grains within the polysilicon thin films at optimal doping and annealing conditions (10(21)/cm(3) of phosphorus and annealed at 1200 degrees C) was responsible for decreasing the impedance. Cyclic voltammetry studies demonstrated that charge storage properties of low doped (10(15)/cm(3)) thin films was 111.4 microC/cm(2) in phosphate buffered saline which compares well with platinum wires (approximately 50 microC/cm(2)) and the double-layered capacitance (C(dl)) could be sustained between -1 to 1 V before breakdown and hydrolysis. We conclude that polysilicon can be optimized for recording and stimulating single neurons and can be a valuable interface material between neurons and CMOS or MEMS devices.

Material Development for Improved 1eV(GaIn)(NAs) Solar Cell Structures

The dilute nitride (GaIn)(NAs) material system grown lattice matched to GaAs or Ge with a 1eV band gap is an interesting material for the use in four-junction solar cells with increased efficiencies. As a result of its metastability, several challenges exist for this material system, which up to now limits the device performance. We performed nanostructural analysis in combination with photoluminescence characterization to optimize the metal organic vapor phase growth as well as the annealing conditions for the quaternary solar cell material. The optimum annealing conditions depend strongly on the In content of the quaternary material. Valence force field calculations of stable N environments in the alloy support the model that the N moves from a Ga rich environment realized during growth into an In rich environment upon annealing. Simultaneously, N induced strain fluctuations, which are detected in the N containing material upon growth, are dissolved and the device properties are improved.

Effect of annealing and initial temperature on mechanical response of a Ni–Ti–Cr shape-memory alloy

The effect of the annealing conditions and the initial temperature on the compressive response of a ternary Ni–Ti–Cr shape-memory alloy is investigated at a strain rate of 10 −3/s, using an Instron hydraulic testing machine. The annealing temperature and duration considerably influence the forward, from austenite to the stress-induced martensite, and the reverse phase transformation. The transition stress and the yield stress of the resulting stress-induced martensite increase with the increasing annealing temperature. The transition stress reaches its maximum value for an annealing temperature of 573 K, and the yield stress for 673 K. Thereafter, both stresses decrease with further increase in the annealing temperature. The highest transition stress is attained for the smallest precipitates. In addition, the phase transformation upon cooling and heating changes from a single-step to a multiple-step with the decreasing annealing temperature. The transition stress for the stress-induced martensite formation increases with increasing initial temperature at a rate of about 8.5 MPa/K. The optimum annealing condition that produces the highest transition and yield stresses without an accompanying residual strain is 573 K for 60 min.

Ge/Si heterojunction photodetector for 1.064 µm laser pulses

Isotype and anisotype heterojunction Ge/Si photodetectors have been made by depositing Ge layer onto monocrystalline Si using vacuum evaporation technique. These detectors before and after annealing were utilized to detect 1.064 µm Nd:YAG laser pulses. The study also includes determination of the optimum Ge thickness and annealing conditions. The experimental results show that the photoresponse highly improve after classical thermal annealing (CTA) and rapid thermal annealing (RTA).The voltage responsivity and rise time results are strongly dependent on annealing type and conditions. It is found that the optimum conditions can be obtained for n-Ge/p-Si photodetector prepared with 200 nm Ge thick and annealed with RTA at 500°C/25 sec.

Investigation of rapid thermal annealing on Cu(In,Ga)Se2 films and solar cells

Rapid thermal annealing (RTA), with fast ramp rate, was performed on several Cu(In,Ga)Se2 (CIGS) films and solar cells under various peak annealing temperatures and holding times. Characterizations were made on CIGS films and cells before and after RTA treatments to study effects of RTA on the CIGS film properties and cell performance. In addition, AMPS-1D device simulation program was used to study effects of defect density on the cell performance by fitting the experimental data of RTA-treated CIGS cells. The results show that RTA treatments under optimal annealing condition can provide significant improvements in the electrical properties of CIGS films and cell performance while preserving the film composition and microstructure morphology.

Overannealing effects in GaInNAs(Sb) alloys and their importance to laser applications

The photoluminescence efficiency and linewidth are well-established metrics for characterizing potential laser active regions. We demonstrate the critical importance of a new parameter for predicting the performance of dilute-nitride lasers: the “optimal” postgrowth annealing temperature, defined as the annealing temperature giving the highest photoluminescence efficiency. We validate this assertion with two 1.55μm edge-emitting GaInNAsSb lasers containing active regions with different optimal annealing temperatures. Although both active regions showed comparable photoluminescence efficiency and linewidth under optimal annealing conditions, laser performance was significantly different. The room-temperature threshold current density for the active region with higher optimal annealing temperature was 630A∕cm2, compared with 2380A∕cm2 for the sample with lower optimal annealing temperature. We conclude that overannealing of the gain region during upper cladding growth is the responsible mechanism. The dependence of the optimal annealing temperature on composition and growth conditions is also discussed.

Influence of annealing atmosphere on ZnO thin films grown by MOCVD

ZnO films were deposited on c-plane sapphire substrates by metal-organic chemical vapor deposition (MOCVD). Annealing treatments for as-deposited samples were performed in different atmosphere under various pressures in the same chamber just after growth. The effect of annealing atmosphere on the electrical, structural, and optical properties of the deposited films has been investigated by means of X-ray diffraction (XRD), atomic force microscope (AFM), Hall effect, and optical absorption measurements. The results indicated that the electrical and structural properties of the films were highly influenced by annealing atmosphere, which was more pronounced for the films annealed in oxygen ambient. The most significant improvements for structural and electrical properties were obtained for the film annealed in oxygen under the pressure of 60Pa. Under the optimum annealing condition, the lowest resistivity of 0.28Ωcm and the highest mobility of 19.6cm2v−1s−1 were obtained. Meanwhile, the absorbance spectra turned steeper and the optical band gap red shifted back to the single-crystal value.

Optical activation of Eu ions in nanoporous GaN films

A systematic optical activation study of Eu-implanted nanoporous GaN films has been carried out as a function of ion dose and annealing temperature. The nanoporous GaN films are prepared by photoelectrochemical etching of n-type GaN films in HF-based electrolyte. Eu ions are implanted in both n-type GaN and n-type porous GaN films at 200keV with doses ranging from 5×1014to5×1015cm−2. For the implantation damage recovery and optical activation of Eu3+ ions, rapid thermal annealing is performed in the temperature range of 900–1200°C under nitrogen ambient. The surface morphology of implanted porous GaN after different processing steps is characterized by scanning electron microscopy and the results show that porous morphology remains uniform even after ion implantation and high temperature processing. Microphotoluminescence and micro-Raman techniques have been used to investigate the optical properties of these Eu-implanted nanoporous films. Postimplantation annealing of both as-grown GaN and porous GaN films leads to the observation of strong photoluminescence (PL) peak around 622nm, which is associated with the D05–F27 intraionic transition of Eu3+ ions. We have observed that PL intensity of Eu-related luminescence peaks increases with annealing temperature up to 1100°C. In addition, due to efficient light extraction by surface nanostructuring, Eu-implanted porous GaN films show much stronger luminescence when compared to Eu-implanted as-grown GaN. Raman spectral analyses also indicate the optimum annealing condition for the implantation damage recovery and the compressive stress state in the Eu-implanted films.