Thermal Cycle Annealing Research Articles

Grain boundaries are Brownian ratchets.

We demonstrate that grain boundaries (GBs) behave as Brownian ratchets, exhibiting direction-dependent mobilities and unidirectional motion under oscillatory driving forces or cyclic thermal annealing. We observed these phenomena for nearly all nonsymmetric GBs but not for symmetric ones. Our observations build on molecular dynamics and phase-field crystal simulations for a wide range of GB types and driving forces in both bicrystal and polycrystalline microstructures. We corroborate these simulation results through in situ experimental observations. We analyze these results with a Markov chain model and explore the implications of GB ratchet behavior for materials processing and microstructure tailoring.

Selected properties of X120Mn12 steel welded joints by means of the plasma-MAG hybrid method

The article describes properties of welds made of high wear resistance X120Mn12 steel obtained by the hybrid PTA-MAG (plasma transferred arc – metal active gas) method. The specimens were 8 mm thick rectangular (200 mm × 350 mm) sheets metal. The analyzed butt welds were made with the parameters selected according to the criterion of smallest cross-sectional area of welds and the narrowest HAZ (heat affected zone). The outcome of metallographic tests of weld, HAZ and parent material, hardness distribution and XRD (X-ray diffraction) patterns of selected areas are presented. The IIT (Instrumented Indentation Test) method was used to describe the distribution of mechanical properties shaped by thermal cycle annealing of the welding process. The investigation shows that the application of the PTA-MAG hybrid heat source for welding manganese steel enables the use of the filler material ER307 (AWS-A5.9). The hybrid PTA-MAG welding system has the relatively high potential to be an efficient alternative to welding standard processes for X120Mn12 steel due to the HAZ overheating limitation. The zone of high-risk weld cracking is the part of the HAZ close to the fusion area that has been reheated during weldment formation. Heat input about 0.6 kJ/mm is needed to provide full deep penetration butt weld without defects and with a vapor capillary of wide enough to cover the weld gap. The increase of hardness in the welded joint is smooth distributed and going up to 10% compared to the base material. The width of HAZ was <1 mm. Intensive carbides precipitation in HAZ has been avoided successfully.

Reversing relaxation-induced embrittlement by high-temperature thermal cyclic annealing in Zr-based metallic glass

Annealing usually induces structural relaxation and reduction of liquid-like regions, leading to embrittlement in bulk metallic glasses (BMGs). Here, we find that the short-term high-temperature thermal cycling (HTC) annealed Zr41.2Ti13.8Cu12.5Ni10Be22.5 (Vit1) BMG shows an improved plasticity without sacrificing their yield strength. And only relaxation behavior with increased hardness is observed after HTC, which is different from the rejuvenation effect usually observed in cryogenic thermal cycling (CTC). We revealed that this embrittlement reversal is attributed to enhanced fluctuations of full width at half maximum (FWHM) of the hardness’ distribution at micrometer and larger scales induced by short-term HTC. The enhanced fluctuations of mechanical heterogeneities across the diameter on a cross-section of the short-term HTC sample may increase the number and decrease the size of shear transformation zones (STZs) activated at high stress and promote the deflection of shear bands (SBs) during their propagation to form multiple SBs. The enhanced plasticity after HTC induced relaxation contradicts the common sense that relaxation accompanying with annihilation of free volume or liquid-like region usually causes embrittlement. Present results indicate that short-term HTC could be a powerful mean to tune the mechanical performance, shedding new lights on the interplay among relaxation, mechanical/structural heterogeneity, and plasticity of MGs.

Carrier Transport Switching of Ferroelectric BTBT Derivative.

Alkylamide-substituted [1]benzothieno[3,2-b][1]benzothiophene (BTBT) derivative of BTBT-NHCOC14H29 (1), which has ferroelectric N-H···O= hydrogen-bonding network of alkylamide group and two-dimensional (2D) electric structure of BTBT π-cores, was prepared to design the external electric field-responsive organic semiconductors. The short-chain derivative of BTBT-NHCOC3H7 (1') revealed the coexistence of a 2D electronic band structure based on the herringbone BTBT arrangement and the one-dimensional (1D) hydrogen-bonding chain. 1 formed a smectic E (SmE) liquid crystal phase above 412 K and showed ferroelectric hysteresis in the electric field-polarization (P-E) curves at 403-433 K. The remanent polarization (Pr) and coercive electric field (Ec) of 1 at 408 K, 0.1 Hz were 24.0 μC cm-2 and 5.54 V μm-1, respectively. By thermal annealing of thin-film 1 at 443 K, the molecular assembly structure of 1 changed from a monolayer to a bilayer structure with high crystallinity, resulting in conducting layers of BTBT parallel to the substrate surface. The organic field-effect transistor (OFET) device with thermally annealed thin-film 1 showed p-type semiconducting behavior with the hole mobility of 1.0 × 10-3 cm2 V-1 s-1. Furthermore, device 1 showed switching behavior of semiconducting properties by electric field poling and thermal annealing cycle. The electric field response of ferroelectrics modulated the molecular orientation and conduction properties of organic semiconductors, resulting in external electric field control of carrier transport properties.

Recoverable tuning of lattice mismatch and strength in ultrastable-nanostructured Cu/Ag spinodoid alloys

The strengthening effect of interface in materials is usually studied by monitoring the change of strength in response to varying structure sizes, such as the varying grain or phase sizes. In this study, we demonstrate that the strength of a nanostructured material can be recoverably tuned by modifying interfacial structure without changing structure size. Specifically, we studied the Cu/Ag spinodoid alloys fabricated by dealloying and electrochemical deposition, which exhibit a cube-on-cube orientation relationship between two interpenetrating nanophases. This material remains stable against coarsening even at temperatures near the eutectic melting point, due to the presence of low-energy semi-coherent interfaces and the lack of defects such as grain boundaries. Using cyclic thermal annealing, we are able to alter the solid solubility of both nanophases and, consequently, the lattice mismatch between them, resulting in a recoverable tuning of hardness and strength. The amplitude of hardness modulation decreases with increasing feature size (λ), and changes sign when λ exceeds ∼500 nm. This is attributed to a competition between two strengthening mechanisms: the interface-induced strengthening that is more prominent at a lower λ, and the solid solution hardening that is largely λ-insensitive. The finding indicates that interface hardening prevails over solution hardening when λ is below ∼500 nm. Current study paves the way for the development of strong and stable nanostructured materials whose properties can be optimized by independently tailoring feature sizes and interfacial structures.

Interface structures of Al0.85Sc0.15N-on-Si thin films grown by reactive magnetron sputtering upon post-growth cyclic rapid thermal annealing

Al0.85Sc0.15N thin films, about 920 nm thick, have been deposited on the Si (001) substrate by reactive magnetron sputtering at 600 °C. X-ray diffraction and pole-figure measurements revealed [0002]-oriented texture structures of the nitride films without any phase separations before and after cyclic annealing at 600–900 °C for up to 48 min. Cross-sectional studies by transmission electron microscopy and energy dispersive x-ray analysis revealed an intermediate Al0.85Sc0.15N layer of ∼24.6 nm thick with smaller grains and tilted [0002]-orientations compared to its overlayer, i.e., a nucleation layer (NL), on the Si substrate. After annealing, apparent morphological changes have been observed at the near-interface regions, including the NL, the NL/Si interface, and the Si substrate, rather than in the Al0.85Sc0.15N overlay. Undesired oxygen has been observed in the nitride film and its composition increased during post-growth thermal annealing without forming oxides. These observations shed new light on crystal growth and post-growth thermal annealing of AlScN toward their high-performance piezoelectric applications.

Dislocation reduction in an MOVPE-grown CdTe/Si epilayer by ex-situ annealing and its effect on the performances of gamma ray detectors fabricated

We studied ex situ thermal cycle annealing on metalorganic vapor phase epitaxy (MOVPE) grown CdTe on (211) Si substrates for dislocation density reduction and its effect on the performance of gamma-ray detector fabricated. The ex situ annealing was performed by varying temperatures from 600 °C to 1000 °C for different anneal durations and cycles varied from 1 to 7 in a hydrogen environment. Gamma-ray detector was fabricated in a p-CdTe/n-CdTe/n+-Si heterojunction diode structure. Dislocation densities were evaluated by the etch pit density (EPD) technique. Dislocation densities were decreased when the annealing temperature was increased above 800 °C. This is due to the annealing enhancing dislocations’ glide motion, which annihilate and reduce their density. The device property could be improved by subjecting the annealing during the early stage of the growth. Devices subjected to annealing showed lower dark current and improved gamma detection property when compared to the devices that were not subjected to annealing during their fabrications.

Molecular beam epitaxy of high-quality GaAs on Si (001) by multi-time thermal cycle annealing

Molecular beam epitaxy of high-quality GaAs on Si (001) by multi-time thermal cycle annealing

Initial study on thermal stability of cold spray tantalum coating irradiated with deuterium for fusion applications

Removal of neutral hydrogen atoms in the plasma edge reduces the number of charge exchange events and thus, the net energy losses in the plasma, significantly improving performance of fusion devices. Effective control of the residual pressure of hydrogen isotopes (HIs) in the plasma edge may be achieved by utilizing a hydrogen absorbing first wall interface capable of withstanding the harsh fusion environment. In this study, we have investigated tantalum (Ta) coating deposited by cold spray technology on 316L stainless steel substrate as a potential plasma-facing material surface. High fluence low energy deuterium plasma irradiation experiments and subsequent thermal annealing cycles associated with thermal desorption spectrometry (TDS) demonstrated superior structural stability of the Ta coating. TDS experiments revealed the outgassing of deuterium (as measure of its retention) for cold spray Ta coatings to be three times higher than bulk Ta and two orders of magnitude greater than bulk polycrystalline W. X-ray photoelectron spectroscopy revealed evolution of oxidation states upon deuterium irradiation and a partial recovery of the metallic signature of Ta after the thermal treatment at 1100 K.

The growth of low-threading-dislocation-density GaAs buffer layers on Si substrates

Monolithic integration of III–V optoelectronic devices on Si platform is gaining momentum, since it enables advantages of low cost, less complexity and high yield for mass production. With the aim of achieving advances in monolithic integration, the challenges associated with lattice mismatch between III–V layers and Si substrates must be overcome, as a low density of threading dislocations (TDs) is a prerequisite for the robustness of the integrated devices. In this paper, we have investigated and compare different types of dislocation filter layers (DFLs) from InGaAs asymmetric step-graded buffer layer (ASG), InGaAs/GaAs strained-layer superlattices, and quaternary alloy InAlGaAs ASG, on the functionality of reducing TD density (TDD) for GaAs buffer layers on Si. Compared to other DFLs, the sample with InAlGaAs ASG buffer layer shows the lowest average TDD value and roughness, while the decrease of TDD in the sample with InAlGaAs ASG buffer layer can be understood in terms of the hardening agent role of aluminium in the InAlGaAs ASG. By further optimising the InAlGaAs ASG through thermal cyclic annealing, we successfully demonstrate a low surface TDD of 6.3 ± 0.1 × 106 cm−2 for a 2 μm GaAs/InAlGaAs ASG buffer layer grown on Si. These results could provide a thin buffer design for monolithic integration of various III–V devices on Si substrates.

GaAs on (001) Si templates for near-infrared InP quantum dot lasers

We investigated the effects of thermal cycle annealing (TCA) at high temperatures on the defect density and morphology of GaAs epilayers grown on (001) Si substrates. Several types of TCA combined with dislocation filter layers (DFLs) were introduced to reduce the defect densities in the GaAs grown on Si substrates. Plan-view transmission electron microscopy shows that the defect density of a 2.7 μm-thick GaAs/Si template with optimized TCA and DFLs is 1.4 × 107 cm−2, lower than a 1.1 μm-thick GaAs/Si template by a factor of 40. The surface roughness of the optimized GaAs/Si template is 1.3 nm after insertion of the DFLs. Additionally, optically pumped InP quantum dot micro-disk lasers (MDLs) were fabricated on these GaAs/Si templates to evaluate the template quality. Room-temperature continuous-wave lasing of 1.5 μm-diameter MDLs was observed, with ultralow lasing thresholds ranging from 0.5 to 2 μW.

Reduced Dislocation of GaAs Layer Grown on Ge-Buffered Si (001) Substrate Using Dislocation Filter Layers for an O-Band InAs/GaAs Quantum Dot Narrow-Ridge Laser.

The development of the low dislocation density of the Si-based GaAs buffer is considered the key technical route for realizing InAs/GaAs quantum dot lasers for photonic integrated circuits. To prepare the high-quality GaAs layer on the Si substrate, we employed an engineered Ge-buffer on Si, used thermal cycle annealing, and introduced filtering layers, e.g., strained-layer superlattices, to control/reduce the threading dislocation density in the active part of the laser. In this way, a low defect density of 2.9 × 107 cm−2 could be achieved in the GaAs layer with a surface roughness of 1.01 nm. Transmission electron microscopy has been applied to study the effect of cycling, annealing, and filtering layers for blocking or bending threading-dislocation into the InAs QDs active region of the laser. In addition, the dependence of optical properties of InAs QDs on the growth temperature was also investigated. The results show that a density of 3.4 × 1010 InAs quantum dots could be grown at 450 °C, and the photoluminescence exhibits emission wavelengths of 1274 nm with a fullwidth at half-maximum (FWHM) equal to 32 nm at room temperature. The laser structure demonstrates a peak at 1.27 μm with an FWHM equal to 2.6 nm under a continuous-wave operation with a threshold current density of ∼158 A/cm2 for a 4-μm narrow-ridge width InAs QD device. This work, therefore, paves the path for a monolithic solution for photonic integrated circuits when III−V light sources (which is required for Si photonics) are grown on a Ge-platform (engineered Ge-buffer on Si) for the integration of the CMOS part with other photonic devices on the same chip in near future.

Low Dark Current and High Speed InGaAs Photodiode on CMOS-Compatible Silicon by Heteroepitaxy

Top-illuminated proof-of-concept indium gallium arsenide (InGaAs) photodiode (PD) array and high speed InGaAs PDs were realized on (001) silicon (Si) substrate by direct heteroepitaxy using metal–organic chemical vapor deposition. The PDs containing InGaAs active layer lattice-matched to InP were grown on Si substrates employing InP-on-Si template with growth technique including GaAs on V-grooved Si, thermal cycle annealing and strained layer superlattice defect filters. Dry etched mesa structure with polyimide passivation was implemented. 8 × 8 InGaAs PD arrays with mesa diameters of 20, 30 and 40 µm were realized on (001) Si, and their performances were benchmarked with identical devices on a native InP substrate. A low dark current density of 0.45 mA/cm² and a responsivity of 0.72 A/W at 1550 nm were measured for 40-µm-diameter device on Si. Directly modulation has also been performed showing a 3-dB bandwidth up to 11.2 GHz and open eye diagram up to 25 Gbps. The imaging performance of InGaAs PD arrays on Si were also demonstrated for the first time by capturing the output beam profile of a single mode fiber at 1550 nm.

Growth and Fabrication of GaAs Thin-Film Solar Cells on a Si Substrate via Hetero Epitaxial Lift-Off

We demonstrate, for the first time, GaAs thin film solar cells epitaxially grown on a Si substrate using a metal wafer bonding and epitaxial lift-off process. A relatively thin 2.1 μm GaAs buffer layer was first grown on Si as a virtual substrate, and a threading dislocation density of 1.8 × 107 cm−2 was achieved via two In0.1Ga0.9As strained insertion layers and 6× thermal cycle annealing. An inverted p-on-n GaAs solar cell structure grown on the GaAs/Si virtual substrate showed homogenous photoluminescence peak intensities throughout the 2″ wafer. We show a 10.6% efficient GaAs thin film solar cell without anti-reflection coatings and compare it to nominally identical upright structure solar cells grown on GaAs and Si. This work paves the way for large-scale and low-cost wafer-bonded III-V multi-junction solar cells.

Growth, characterization and theoretical optical properties of polycrystalline n-silicon thin films for oxide-silicon tandem cells

With the decline in fossil fuels, hydrogen-based alternatives provide a reliable and clean source for sustainable energy generation. In these endeavors, photochemical splitting for hydrogen production through tandem cells has been the source of much theoretical and experimental research in science. Much focus has been placed on interfacial band gap engineering as one of the most promising routes in the generation of hydrogen. This present work explores sputtering of n-silicon to form the active electrode in a n-Si ∣ n-TiO2 tandem cell and investigates the effect of variations in sputtering and post sputtering treatment parameters (rapid thermal annealing and long cycle annealing) for successful deposition of crystalline Silicon. The samples were successfully characterized via Raman Spectroscopy, x-ray Diffraction and Optical Transmission Spectroscopy to ascertain prevalent crystalline order and optical band gap, under different sputtering and post-sputtering conditions. Relevant conclusions to ascertain the best possible n-Si deposition parameters indicated the use of post-sputtering annealing to induce and enhance crystallinity but to be cautious as not to incur the loss of Si during the annealing process.

GaAs-based optoelectronics grown on GaAs/Si virtual substrates with multiple spaced thermal-cycle annealing

This paper describes the growth of a GaAs-based light-emitting diode (LED) on a GaAs/Si virtual substrate by metalorganic chemical vapor deposition. A GaAs/Si virtual substrate (or template) was formed by depositing a 3.5-μm-thick GaAs epilayer on a (100) Si substrate with the employment of multiple spaced thermal-cycle annealing (TCA). The number of annealing cycle was zero to five in this study to examine crystallinity variation of a GaAs/Si template. High-resolution X-ray rocking curve analysis showed that (400) GaAs crystallinity in terms of full width at half maximum (FWHM) improved significantly with the number of the spaced TCA and then reached a minimum at four annealing cycles. There seems to be no significant difference in crystallinity between the GaAs/Si templates with four and five spaced annealing cycles. The GaAs/Si template with four spaced annealing cycles demonstrated not only an excellent (400) FWHM value of 94.6 arcsec but also a reduced dislocation density of 2.4 × 107 cm−2 evaluated from plan-view transmission electron microscopic observation. Electroluminescence spectra of GaAs-based LEDs grown on GaAs/Si templates showed that emission peak intensity increased monotonically with the number of the spaced annealing cycles. Furthermore, the emission peak intensity of a LED grown on the GaAs/Si template with five spaced annealing cycles reached 80% of a reference LED grown on a GaAs substrate, indicating that the presented multiple spaced TCA method may be useful in obtaining superior crystallinity of a GaAs/Si template for the potential application of monolithic integration of optoelectronic devices with Si.

Selective area heteroepitaxy of low dislocation density antiphase boundary free GaAs microridges on flat-bottom (001) Si for integrated silicon photonics

Integrating III–V gain elements in the silicon photonics platform via selective area heteroepitaxy (SAH) would enable large-scale and low-cost photonic integrated circuits. Here, we demonstrate antiphase boundary (APB)-free gallium arsenide (GaAs) microridges selectively grown on flat-bottom (001) silicon (Si) inside a recess. This approach eliminates the need for etching the patterned Si to form trapezoid or v-groove shapes, often leveraged for eliminating APBs. A low surface dislocation density of 8.5 × 106 cm−2 was achieved for 15-μm-wide GaAs microridges, quantified by electron channeling contrast imaging. The avoidance of APBs is primarily due to their self-annihilation, influenced by the sufficiently low temperature GaAs nucleation and subsequent higher temperature buffer overgrowth. Dislocation filtering approaches, namely, thermal cycle annealing and strained-layer superlattices, have been applied to effectively reduce the dislocation density. SAH of GaAs on trapezoidal-shaped Si pockets is also reported to illustrate the differing growth conditions for GaAs on (001) and (111) Si microplanes.

Monolithic growth of GaAs laser diodes on Si(001) by optimal AlAs nucleation with thermal cycle annealing

A GaAs quantum-well laser diode was directly grown on silicon (001) substrate by a hybrid technique comprising AlAs nucleation and thermal cycle annealing. The hybrid technique provided the advantages of superior surface roughness, high quantum efficiency, and low threading dislocation density (TDD) of a thin buffer. The TDD was quantitatively characterized through the electron channeling contrast imaging method. Directly grown GaAs on Si exhibited a TDD of 5.45 × 107 /cm2 with small thickness of approximately 1.5 µm. The roughness and quantum efficiency of GaAs on Si was enhanced by adopting the nucleation layer of AlAs. We found that there exists an optimal thickness of AlAs nucleation to be 1.68 nm through structural and optical analysis. Based on optimized GaAs on Si, the GaAs quantum-well laser diode was directly grown with a TDD of 2.5 × 107 /cm2. Whole epitaxial layers were grown by metalorganic chemical vapor deposition. An edge-emitting broad stripe laser diode was successfully fabricated with a cavity length and width of 1120 µm and 60 µm, respectively. The continuous-wave lasing at room temperature was realized with a threshold current density of 643 A/cm2 and maximum output power of 19.7 mW at a single facet, where a threshold current density of 317 A/cm2 was obtained under pulsed operation condition. This result would constitute a building block to realize silicon-based on-chip light sources.

High-quality AlN/sapphire templates prepared by thermal cycle annealing for high-performance ultraviolet light-emitting diodes

Thermal cycle annealing (TCA) is introduced to accelerate the dislocation annihilation in sputter-deposited AlN films on sapphire. Compared with constant temperature annealing, AlN films processed by TCA showed lower dislocation densities, smoother surface morphology, and fewer defects generated from the AlN/sapphire interface. After optimizing the film thickness, AlN films with a thickness of 800 nm, and X-ray rocking curve full widths at half maximum of 10–20 arcsec (0002) and 80–90 arcsec (10-12) were demonstrated, providing a simple and low-cost way to prepare high-quality AlN/sapphire templates for high-performance ultraviolet light-emitting diodes.

The rapidly reversible processes of activation and deactivation in amorphous silicon heterojunction solar cell under extensive light soaking

Silicon heterojunction (HJT) solar cells use hydrogenated amorphous silicon (a-Si:H) to form passivating contacts. To obtain high performance, many crucial applications have been confirmed and introduced. In this work, extensive light soaking (ELS) was used to comprehensively investigate a-Si:H films and HJT solar cells. The enhanced effective minority carrier lifetime (τeff) for c-Si wafers passivated with a-Si:H was achieved via extensive light soaking, and the passivation enhancement can reach saturation in few seconds. It was observed that there was a significant contribution of low thermal annealing (LTA) process, excellently improving the ultimate passivation function of ELS. A comparison of c-Si wafers passivated with different a-Si stacks under various temperatures was examined, and the activation and deactivation performance during repeated extensive light soaking-low thermal annealing cycles was systematically discussed. Finally, the reversibility of efficiency enhancement and degradation in HJT solar cells related to extensive light soaking-low thermal annealing cycles was demonstrated for the first time.