Rapid Thermal Annealing Technique Research Articles

Improvement of energy storage performance in PbZr0.52Ti0.48O3/PbZrO3 multilayer thin films via regulating PbZrO3 thickness

In this work, to prepare the PbZr0.52Ti0.48O3(PZT)/PbZrO3(PZ) multilayer films, PZ films and PZT films were spin-coated on LaNiO3/SiO2/Si substrates in sequence by the sol-gel method, and the PZ films were prepared using PZ precursor solution with different concentrations. After each spin-coating, PZ layer and PZT layer were annealed with rapid thermal annealing (RTA) technique at 650 °C and 550 °C, respectively. The crystal structures, microstructures and electrical properties of the films with different PZ film thickness were comprehensively investigated. The PZ films with different thickness showed perovskite phase. The PZT films on crystallized PZ films exhibited the coexistence of pyrochlore phase and perovskite phase at the annealing temperature of 550 °C. The PZT/PZ multilayer films with 0.2 M PZ precursor solution exhibit typical anti-ferroelectricity with double hysteresis loops, while other multilayer films exhibit nearly linear loops. In addition, the recoverable energy storage density increases with the increase of the film thickness and reaches the maximum value 32.4 J/cm3 in the PZT/PZ multilayer films with 0.4 M PZ precursor solution. Therefore, the ferroelectric properties of the PZT/PZ multilayer films could be regulated by different PZ film thickness, which effectively further enhances the energy storage performance.

Rapid thermal processing of garnet-based composite cathodes

Rapid thermal annealing techniques enable quick and non-contact processing of ceramic materials and are particularly promising for materials containing elements with high vapor pressure. For example, Li-ion conductive oxide-ceramics such as the garnet-type Li7La3Zr2O12 (LLZO) need to be densified in order to be used as separators or in composite cathodes of all-solid-state batteries (ASB), but suffer from lithium loss at elevated temperatures. To address this issue, the sintering method “rapid thermal processing” (RTP) is used to fabricate ceramic composite cathodes of LLZO and LiCoO2 (LCO), the cathode active material. The cathodes were deposited on LLZO separators by screen-printing, a scalable industrial process for the fabrication of ceramic components. A detailed analysis by Raman spectroscopy and X-ray diffraction analysis confirms the successful mitigation of secondary phase formation between LCO and LLZO. The subsequent application of In-metal anodes resulted in fully inorganic ASB that were electrochemically cycled.

Excimer Laser Patterned Holey Graphene Oxide Films for Nonenzymatic Electrochemical Sensing.

The existence of point defects, holes, and corrugations (macroscopic defects) induces high catalytic potential in graphene and its derivatives. We report a systematic approach for microscopic and macroscopic defect density optimization in excimer laser-induced reduced graphene oxide by varying the laser energy density and pulse number to achieve a record detection limit of 7.15 nM for peroxide sensing. A quantitative estimation of point defect densities was obtained using Raman spectroscopy and confirmed with electrochemical sensing measurements. Laser annealing (LA) at 0.6 J cm-2 led to the formation of highly reduced graphene oxide (GO) by liquid-phase regrowth of molten carbon with the presence of dangling bonds, making it catalytically active. Hall-effect measurements yielded a mobility of ∼200 cm2 V-1 s-1. An additional increase in the number of pulses at 0.6 J cm-2 resulted in deoxygenation through the solid-state route, leading to the formation of holey graphene structure. The average hole size showed a hierarchical increase, with the number of pulses characterized with multiple microscopy techniques, including scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. The exposure of edge sites due to high hole density after 10 pulses supported the formation of proximal diffusion layers, which led to facile mass transfer and improvement in the detection limit from 25.4 mM to 7.15 nM for peroxide sensing. However, LA at 1 J cm-2 with 1 pulse resulted in a high melt lifetime of molten carbon and the formation of GO characterized by a high resistivity of 3 × 10-2 Ω-cm, which was not ideal for sensing applications. The rapid thermal annealing technique using a batch furnace to generate holey graphene results in structure with uneven hole sizes. However, holey graphene formation using the LA technique is scalable with better control over hole size and density. This study will pave the path for cost-efficient and high-performance holey graphene sensors for advanced sensing applications.

Mode-locked all-fiber laser with high stability based on cobalt oxyfluoride

Recent years have witnessed the exploration of fiber laser technology focused on numerous pivotal optoelectronic applications from laser processing and remote sensing to optical communication. Here, using cobalt oxyfluoride (CoOF) as the nonlinear material, a 156 fs mode-locked fiber laser with strong stability is obtained. The rapid thermal annealing technique is used to fabricate the CoOF, which is subsequently transferred to the tapered region of the microfiber to form the effective pulse modulation device. CoOF interacts with the pulsed laser through the evanescent field to realize the intracavity pulse shaping, and then the stable mode-locked pulse is obtained. The mode-locked operation is maintained with the pulse duration of 156 fs and repetition rate of 49 MHz. In addition, the signal-to-noise ratio is about 90 dB. Those experimental results confirm the attractive nonlinear optical properties of CoOF and lay a foundation for the ultrafast application of low-dimensional transition metal oxides.

Enhanced photoluminescence of WS2/WO3 heterostructural QDs

Abstract Tungsten disulfide (WS2), as one of the typical transition-metal dichalcogenides (TMDCs), possesses attractive physical properties and widely potential applications, especially in optoelectronic devices. However, the low photoluminescence (PL) quantum yield (QY) still limits the practical applications of WS2. In this paper, WS2/WO3 heterostructural (core/shell) quantum dots (QDs) are prepared by pulsed laser deposition (PLD) and rapid thermal annealing (RTA) techniques, which exhibit PL enhancement and higher PLQY. The improvement may originate from the WO3 shells, which act as passivation layer to relieve the surface defect-states and many-body effects. Our work may provide a new pathway to utilize the heterostructural QDs to design physical properties of TMDCs, and these heterostructural QDs are promising candidates in optoelectronic applications such as photodetectors and light-emitting devices.

Synthesis and Characterization of a-Si<sub>x</sub>C<sub>y</sub> Thin Films Prepared by RF Magnetron Co-Sputtering Technique

Si-C based alloys have attracted much attention due to their potential applications in electronic and optical devices. In this paper, a-SixCy thin films with different Silicon (Si) content are obtained by sputtering of SiC; co-sputtering of SiC and Si targets at different deposition temperatures (Td) such as 200oC, 350oC and 500oC. It is annealed at various annealing temperature (Ta) using conventional thermal annealing (CTA) and Rapid Thermal Annealing (RTA) techniques. The effect of excess Si incorporation and the unintentional oxidation during various stages of sample preparation are discussed. Their structural and optical properties are investigated using spectroscopic ellipsometry, X-Ray Diffraction spectroscopy (XRD), and Fourier Transform Infrared spectroscopy (FTIR). The refractive index value (n1.95eV) varies between 1.6 to 3.6, suggesting the transition from porous silicon carbide to Si-rich silicon carbide or silicon oxycarbide upon increasing Td and Ta, which is also supported by the FTIR spectra. The emergence of absorption peak between ~950 cm−1 and 1100 cm−1 with the increase of Ta and excess silicon is attributed to Si-O a stretching vibration bond which is an indication of Si richness and unintentional oxidation during annealing. Detailed analysis on the process parameters and the evolution of phase transformations are discussed.

Crystallographic inversion-mediated superparamagnetic relaxation in Zn-ferrite nanocrystals

Crystallographic inversion induced shift of resonance frequency in zinc ferrite nanoparticle (ZF-NP) samples is studied here. ZF-NP samples were synthesized by a solution-based, low-temperature (<200 °C), microwave-assisted solvothermal (MAS) process. Owing to the far-from-equilibrium processing condition, the MAS process produces a very high degree of crystallographic inversion, δ=0.61, in the as-synthesized nanocrystallites. A rapid thermal annealing (RTA) technique was adopted to tune-down crystallographic inversion without altering the crystallite sizes in annealed samples. The crystal structures, particle shapes, and compositions of the nanocrystalline samples were characterized by XRD, SEM and Raman spectroscopy. The samples are phase-pure, with particle size in the range 8-16 nm and their compositions are stoichiometrically accurate. The resonance phenomena in 1 to 10 GHz frequency range was measured by analyzing the impedance mismatch of a microstrip line with the magnetic material loaded on to it. The RTA protocol enables tuning of the resonance phenomena in the ZF-NC samples above 6 GHz with tunable range of ∼500 MHz

(Invited) Ion Implantation and Activation of n- and p-Type Dopants in GaN

GaN-based power switching devices are of significant interest for high efficiency power conversion circuits in medium voltage applications. However, there are still significant challenges preventing mass production and widespread adoption. Recently, GaN-based vertical and lateral power devices have attracted significant interest due to promising device results coupled with progress in native substrate, epitaxial growth, and processing technology developments. However, there are two significant limiting factors for vertical GaN power devices at present. The first issue is substrate and epitaxial layer uniformity and reliability, and the second is the lack of a planar selective-area doping process. While p-type epitaxial growth capability and the ability to stack layers are quite mature from the LED industry, power devices require planar selective-area doping, which is a routine step by ion implantation in the Si and SiC device industry. The ability to implant and activate dopants, particularly p-type dopants, in GaN still remains a challenge as implant activation typically requires annealing at temperatures ~ 2/3 of the melting point, which is a region where the GaN crystal is unstable and readily decomposes to Ga + N2 at atmospheric pressure. The NRL-developed symmetric multicycle rapid thermal annealing (SMTRA) technique has been the most successful, demonstrating electrical activation of up to ~10% of the implanted Mg dopant atoms using a combination of a temporary, thermally stable capping layer, annealing in a moderate nitrogen overpressure, and performing a well-optimized annealing temperature profile including multiple spike anneals. Advances in the SMRTA process development, including optimization of capping processes, implantation profile, and processing steps such as metallization and surface treatments will be reviewed here. In addition, the evaluation of components of the SMRTA process, such as the cap and overpressure anneal, have been applied to Si implantation for n-type doping and will be presented here. This is a critical step to reduce contact resistance in lateral GaN structures as well as form the source regions of vertical devices that is typically accomplished by selective area regrowth. The use of ion implantation and activation utilizes fewer process steps and avoids impurity incorporation at sidewalls compared to the selective area regrowth process, and has been shown to yield lower contact resistance as well. This presentation will review advances in both Mg and Si ion implantation and assess the viability of this process for practical device fabrication.

Study of the Electrical and Diffusion Barrier Properties in Ultrathin Carbon Film-Coated Copper Microwires for Interconnects

Four specimen patterns with the microstructure of a microcopper wire are deposited on the Si-wafer substrate plus thermal oxide (SiO2) film as the top layer. Each pattern was prepared to have two kinds of specimens, including with and without ultrathin carbon film between the copper wire and the top layer (SiO2). The effect of carbon film on electrical properties is evaluated via the measurements of the I (current)–V (voltage) curve, sheet electrical resistance, current leakage, and its ratio and effective permittivity. A rapid thermal annealing (RTA) technique is provided as an economic and efficient method to grow the ultrathin carbon film rapidly as the interlayer. Appropriate choices of 900 °C and 3 min as the annealing temperature and time can produce ultrathin carbon film with nearly 100% coverage of the copper surface. The sheet resistance of specimen demonstrates the behavior exactly opposite to that of the carbon film coverage of wire surface. The combined effect of elevating the voltage and annealing temperature of the specimen with carbon film on the current leakage is much lower than that arising in the specimen without carbon film, so long as the carbon films operating at that temperature (between 350 and 500 °C) are still sustainable. The differences in current leakage and effective permittivity between these two kinds of specimen are significantly increased by raising the temperature. The intensity (IC) of copper diffusions into the SiO2 layer in the specimens with the carbon film demonstrates behavior similar to that of current leakage (CL). The IC and CL values for the temperatures ≦ 350 °C are much lower than those obtained at 500 °C.

Brilliant blue, green, yellow, and red fluorescent diamond particles: synthesis, characterization, and multiplex imaging demonstrations.

Until recently, the number of emission colors available from fluorescent diamond particles was primarily limited to red to near-infrared fluorescence from the nitrogen-vacancy color center in type Ib synthetic diamond and green fluorescence associated with the nitrogen-vacancy-nitrogen center in type Ia natural diamond. Using our recently reported rapid thermal annealing technique, we demonstrate the capability of producing fluorescent diamond particles that exhibit distinctive blue, green, yellow, and red fluorescence from the same synthetic diamond starting material. Utilizing these multiple colored diamonds, we analyze their fluorescence characteristics both in-solution as well as on-substrate and additionally evaluate their viability in simple multiplex imaging and cellular bioimaging experiments. While there are still challenges associated with their immediate use in traditional multiplex imaging, this novel approach opens new opportunities to enhance the capability and flexibility of fluorescent diamond particles at the nanoscale.

Characteristics of hetero‐structured thermoelectric devices with a ‐ Si / Mg 2 Si‐stacked thin film layers

New high-quality thermoelectric devices with amorphous silicon/magnesium silicide (a-Si/Mg2Si)-stacked hetero-structure thin film layers have been fabricated using both radio frequency sputtering and rapid thermal annealing techniques. The thermoelectric properties of the a-Si/Mg2Si hetero-structure layers were found to be much superior to those of the a-Si layer.

An experimental study of a-Si/ZnO-stacked hetero-structures for potential thermoelectric energy harvesting applications

Here, we present a study of thermoelectric devices with amorphous silicon/zinc oxide (a-Si/ZnO)-stacked hetero-structures fabricated using both radio frequency magnetron sputtering and rapid thermal annealing techniques. Overall, the Seebeck coefficient (S) and power factor (S2σ, where σ is the electrical conductivity) of the a-Si/ZnO-stacked hetero-structures were found to be superior to those of pure a-Si structures. In particular, the Seebeck coefficient and power factor of the a-Si/ZnO (9/8 layers)-stacked hetero-structures were about 1.6 and 23.8 times those of the pure a-Si structures, respectively. These improvements can be attributed to hole blocking by the a-Si/ZnO potential barriers formed at the interface between the ZnO layer with a wide energy bandgap and the a-Si layer with a relatively narrow bandgap. In addition, the a-Si and ZnO materials used in this work are non-toxic, earth-abundant, and cheap, and the fabrication processes were simple and cost-effective, making the hetero-structures suitable for use in non-toxic and biocompatible thermoelectric devices and also for micro-energy harvesting applications.

Reduction of yellow and blue luminescence in Si-doped GaN by rapid thermal annealing

Si-doped GaN films grown by metal organic chemical vapour deposition have been annealed under different annealing conditions in N2 ambient. The annealed films have been characterized by photoluminescence and high resolution X-ray diffraction. The results show that the rapid thermal annealing (RTA) treatment suppresses the yellow and blue luminescence bands in the annealed Si-doped GaN films. For the sample annealed at 850 °C for 3 min, the yellow and blue band intensities even decreases by approximate one order of magnitude over the as-grown sample. In addition, the densities of the edge and screw threading dislocations in the Si-doped GaN also decrease after the RTA treatment. These facts provide the evidence that the RTA technique can effectively improve the crystalline quality of the Si-GaN films.

Enhanced hole concentration in nonpolar a-plane p-AlGaN film with multiple-step rapid thermal annealing technique

An innovative multiple-step rapid thermal annealing (RTA) technique was developed for obtaining high hole concentration in the nonpolar a-plane Mg-delta-doped AlGaN films grown on semi-polar r-plane sapphire substrates with metal organic chemical vapor deposition. The structural, optical, and electrical properties of the nonpolar a-plane p-AlGaN epi-layers were characterized with high-resolution x-ray diffraction, photoluminescence spectra, and Hall effect measurement. The characterization results demonstrated that the dissociation efficiency of the Mg–H bonds in the nonpolar a-plane p-AlGaN films could be improved significantly with the multiple-step RTA process. In fact, a hole concentration as high as 1.9 × 1018 cm−3 was achieved with the multiple-step RTA technique, which was 35%, 9%, and 23% higher than those obtained with conventional one-step, two-step, and the recently renovated two-step RTA methods, respectively.

Influences of oxygen vacancies on the enhanced nonlinear optical properties of confined ZnO quantum dots

Confining ZnO quantum dots (QDs) into a solid state matrix to form nanocomposite materials is an important mean to design nonlinear optical devices. In this paper, ZnO confined in Al2O3 matrix are synthesized by pulsed laser deposition method and rapid thermal annealing technique. The substantial oxygen vacancies are generated in the N2-annealed ZnO QDs. Magnetic measurements illustrate that the ferromagnetic nature of ZnO QDs confined in Al2O3 matrix can be due to the oxygen vacancies. The determined two-photon absorption in N2-annealed ZnO QDs is an instantaneous nonlinear process and is enhanced almost 2 times compared to that of O2-annealed ZnO QDs. The enhancement of optical nonlinearities achieved in confined ZnO QDs with substantial oxygen vacancies is important for the practical applications of ZnO nanostructures in such as optical limiting devices and all-optical switching elements.

(Invited) Vertical GaN Devices Enabled By Selective Area P-Type Doping

A key element for enabling high performance vertical GaN power electronic devices is the capability to realize selective area p-type doping. The ability to arbitrarily define p-type regions through ion implantation eliminates the need for epitaxial regrowth on etched surfaces, which is currently a well-known technological roadblock. However, activation of implanted Mg is also a challenge, since activation of the Mg acceptors requires annealing at temperatures above the thermodynamic stability limits of GaN in atmosphere. Implementing the symmetric multi cycle rapid thermal annealing (SMTRA) technique has been shown to activate up to ~10% of the implanted Mg dopant atoms. This technique includes a temporary thermally stable capping layer, annealing in a nitrogen overpressure, and performing a well-optimized annealing temperature profile including multiple spike anneals. Vertical GaN junction barrier Schottky (JBS) diodes and Schottky barrier diodes (SBDs) with implanted junction termination extension (JTE) are demonstrated using the SMRTA process, as are process module development toward trench MOSFET devices.

Strain-induced fcc Fe nanocrystals confined in Al2O3 matrix

It is well known that the face-centered cubic (fcc) Fe is thermodynamically unstable at ambient conditions. In this paper, we theoretically and experimentally demonstrate that thermodynamically stable fcc Fe nanocrystals can be induced by external strain at room temperature. Fe nanocrystals confined in non-magnetic Al2O3 matrix are fabricated using pulsed laser deposition method and rapid thermal annealing technique. During the growth process, the confined Fe nanocrystals experience net deviatoric strain from the Al2O3 matrix, which can modify the microstructures of the confined Fe nanocrystals and lead to the formation of thermodynamically stable fcc Fe nanocrystals (space group Fm-3m) at room temperature. First-principles calculations also demonstrate that the strained Fe nanostructure with fcc phase is more thermodynamically stable. A typical behavior of weakly interacting Fe nanocrystals is observed, characterized by a superparamagnetic regime and a blocking of particle moments centered at TB (∼9 K).

Strain Engineered Band Structure and Optical Properties of Confined GaAs Quantum Dots

Understanding the physics that correlate strain and physical properties of quantum dots (QDs) is crucial for technology applications. In this paper, GaAs QDs confined in Al2O3 matrix are synthesized using the pulsed laser deposition method and rapid thermal annealing technique. It is revealed that the confined GaAs QDs experience compressive strain during the growth process. The strain can be used to improve and tailor the optical properties of confined GaAs QDs by engineering the bandgap and thus the photoluminescence emission band to a distinct wavelength. These findings presented here can engineer the properties of GaAs QDs for potential application in optoelectronic and photonic devices.

Low-Temperature Ohmic Contact Formation in AlN/GaN HEMT Using Microwave Annealing

In this brief, a low-temperature microwave annealing (MWA) method is demonstrated for the formation of ohmic contact to AlN/GaN high electron mobility transistors (HEMTs) for the first time. Compared with the traditional rapid thermal annealing (RTA) technique, MWA-HEMT can achieve a comparable low ohmic contact resistance with much smoother surface of ohmic contacts. Transmission electron microscopy results show that no direct current path connecting the 2-D electron gas and the metal is formed. Temperature-dependent contact resistance measurement indicates that field emission tunneling dominates the current transport mechanism in ohmic contact formation. The maximum dc output current density of 1.4 A/mm and the peak extrinsic transconductance ( ${G}_{\textsf {m}}$ ) of 270 mS/mm are measured on ${2} \times {8} \,\,{\sf \mu } $ $m^2$ gate MWA-HEMTs. Besides, MWA-HEMTs have higher ${I}_{ \mathrm{ ON}}/{I}_{ \mathrm{ OFF}}$ ratio due to the lower gate leakage current than that of RTA-HEMTs.

High performance Ge ultra-shallow junctions fabricated by a novel formation technique featuring spin-on dopant and laser annealing for sub-10 nm technology applications

In this work, we explored a novel technique for the formation of ultra-shallow p+/n and n+/p junctions on Ge substrate using the spin-on dopant (SOD) followed by laser annealing (LA). The junction depth and doping profiles were extracted and compared between Ge junctions activated by LA and by the conventional rapid thermal annealing (RTA). It is experimentally confirmed that the process of SOD followed by LA method outperformed that by RTA technique in terms of the ultra-shallow junction depth, higher surface doping concentration and steeper doping profiles. Therefore, the high performance Ge p+/n and n+/p junctions fabricated by SOD followed by LA method exhibit suppressed junction leakage current and raised on/off ratios, making this novel technique a promising way for source/drain formation in future technology nodes.