Thermal Cycle Annealing Research Articles

High performance germanium-on-silicon detectors for optical communications

We demonstrate fast and efficient germanium-on-silicon p-i-n photodetectors for optical communications, with responsivities as high as 0.89 and 0.75 A/W at 1.3 and 1.55 μm, respectively, time response <200 ps and dark currents as low as 1.2 μA. Ge was epitaxially grown on Si by chemical vapor deposition, employing a low temperature buffer and cyclic thermal annealing to reduce the dislocation density. The overall performance is well suited for >2.5 Gb/s integrated receivers for the second and third fiber spectral windows.

Improved morphology and crystalline quality of MBE CdZnTe/Si

We report on continuing efforts to develop a reproducible process for molecular beam epitaxy of CdZnTe on three-inch, (211) Si wafers. Through a systematic study of growth parameters, we have significantly improved the crystalline quality and have reduced the density of typical surface defects. Lower substrate growth temperatures (∼250–280°C) and higher CdZnTe growth rates improved the surface morphology of the epilayers by reducing the density of triangular surface defects. Cyclic thermal annealing was found to reduce the dislocation density. Epilayers were characterized using Nomarski microscopy, scanning electron microscopy, x-ray diffraction, defect-decoration etching, and by their use as substrates for HgCdTe epitaxy.

Annealing cycle number dependence of magnetoresistance in alloy NiMn-pinned spin valves

NiMn-pinned spin valve films with the stacks of Glass/NiFe/Co/Cu/Co/NiFe/NiMn/Ta were made by DC magnetron sputtering and the annealing cycle number dependence of magnetoresistance in the films was investigated. By optimizing the process of deposition and post thermal annealing cycle, we obtained the NiMn-spin valve films with MR ratio of 2.5%, exchange coupling field of 620 Oe, and coercivity of 250 Oe for the pinned layer. The exchange coupling field maintained its strength in operation up to 175°C and decreased monotonically to zero at 380°C.

Effect of Crystal Orientation on Dielectric Properties of Lead Zirconium Titanate Thin Films Prepared by Reactive RF-Sputtering

Theoretical calculations based on phenomenology of ferroelectrics have been previously reported for lead zirconium titanate (PZT) system. This paper offers an experimental comparison of the crystal orientation dependence of dielectric properties for PZT thin films grown using reactive RF-sputtering. Highly oriented PZT thin films with a rhombohedral composition have been grown in different orientations using selective rapid thermal annealing cycles. The PZT(100) oriented films showed larger dielectric constant and loss compared to PZT(111) films. The PZT(100) films possessed sharp square-like hysteresis loops indicating a instantaneous switching of domains at the coercive field whereas the PZT(111) films showed smooth hysteresis loops as expected from our phenomenological calculations.

Residual strain and threading dislocation density in InGaAs layers grown on Si substrates by metalorganic vapor-phase epitaxy

InGaAs layers with In contents between 0.007 and 0.055 have been grown on GaAs epilayers on Si substrates by low-pressure metalorganic vapor-phase epitaxy. The threading dislocation density of the order of 105 cm−2 in the InGaAs layer was achieved by insertion of an InGaAs strained layer combined with thermal cycle annealing. Photoluminescence measurement for layers confirmed that the residual strain was lower in InxGa1−xAs layers with x⩾0.038 than that in GaAs. It is suggested that the tensile strain due to the difference in the thermal expansion coefficient between InGaAs and Si materials was compensated by the compressive strain partly due to the slow strain relaxation by work hardening in InGaAs layers grown on GaAs layers or due to the incomplete strain relaxation in InGaAs layers at the small thickness of 1 μm.

Improvement of the MOCVD-grown InGaP-on-Si towards high-efficiency solar cell application

The thermal cycle annealing (TCA) for GaAs layer grown on Si substrate (GaAs/Si) increased the photoluminescence (PL) intensity of InGaP epilayer which was regrown on the GaAs/Si substrate by about 100 times. The full-width at half-maximum (FWHM) of double-crystal X-ray diffraction (DXRD) was decreased from 313 to 251 arcsec. From the electron-beam-induced current (EBIC) image measurements, the defect-related dark spots density (DSD) of the regrown InGaP layer was reduced by about 30% by using TCA GaAs/Si substrate. This means that TCA treatment for GaAs layer effectively increased the crystal quality of InGaP epilayer regrown on GaAs/Si substrate (InGaP/GaAs/Si). The PL intensity of InGaP epilayer was also enhanced due to the passivation of the residual defect-related nonradiative recombination centres by post-growth phosphine (PH 3/H 2=10%) plasma exposure.

Silicon-on-insulator: materials aspects and applications

The purpose of this contribution is to give an overview of silicon-on-insulator (SOI) technology with emphasis on the fabrication of SOI substrates and their material properties. Although the concept of SOI has been around for several decades, only recent material science advances made the fabrication of thin-film substrates possible whose material quality is comparable to bulk wafers. SIMOX wafers benefitted from lowering the oxygen dose needed for ion-beam synthesis of buried oxide layers and optimisation of the thermal annealing cycles. Through improved thinning technologies, the wafer-direct-bonding approach for the burial of thermal oxide layers became competetive for thin-film SOI, especially when complemented with the salvaging of the “sacrificial” wafer.

Efficient high-speed near-infrared Ge photodetectors integrated on Si substrates

We have fabricated Ge/Si heterojunction photodetectors with high responsivities of 550 mA/W at 1.32 μm and 250 mA/W at 1.55 μm and time responses shorter than 850 ps. High quality Ge was epitaxially grown on Si using ultrahigh vacuum/chemical vapor deposition followed by cyclic thermal annealing. The beneficial effect of the post-growth thermal annealing on the electrical properties of Ge epilayers, due to the reduction of threading-dislocation densities, is confirmed by the dramatic enhancement of the performance of the photodetectors.

Material issues in the 100 T non-destructive magnet

The effort in materials program related to the first 100 T non destructive (100 T ND) magnet has been concentrated on four areas: (a) development of the fabrication routes for various conductive wires in collaboration with other institutes and industrial partners, (b) investigation of the properties of a variety of candidate high strength high conductivity materials, (c) selection of the reinforcement materials for the coils and development of fabrication routes for these materials, (d) characterization of the commercially available insulation materials. This paper deals with the conductor issues. The properties and the microstructure of Cu-Ag, UNS-C157XX (Cu-Al/sub 2/O/sub 3/), Cu+Stainless Steels (SS) and Cu-Nb composites have been investigated for their potential use as conductors in pulsed high field magnets. These conductors demonstrate a combination of good conductivity, high strength, adequate workability, and the availability of final section sizes needed for the magnet design. Examination of the initial portion of the stress strain curve of cold worked conductors reveals that the internal stresses developed during the fabrication influence the mechanical response of the materials. Thus, the properties of the drawn materials have been measured as a function of cyclic loading and thermal annealing cycles, and the cyclic properties are related to the internal stresses.

High-quality Ge epilayers on Si with low threading-dislocation densities

High-quality Ge epilayers on Si with low threading-dislocation densities were achieved by a two-step ultrahigh vacuum/chemical-vapor-deposition process followed by cyclic thermal annealing. On large Si wafers, Ge on Si with threading-dislocation density of 2.3×107 cm−2 was obtained. Combining selective area growth with cyclic thermal annealing produced an average threading-dislocation density of 2.3×106 cm−2.We also demonstrated small mesas of Ge on Si with no threading dislocations. The process described in this letter for making high-quality Ge on Si is uncomplicated and can be easily integrated with standard Si processes.

Reduction of threading dislocations in GaAs on Si by the use of intermediate GaAs buffer layers prepared under high V–III ratios

We have shown that the insertion of a GaAs layer prepared by organometallic vapor phase epitaxy under very high (VH) V–III ratios into a GaAs/Si epitaxial structure improves its crystallinity after thermal cycle annealing (TCA). The PL intensity of the upper GaAs epilayer with the VH-V/III GaAs intermediate buffer layer is found to be larger than that with a normal GaAs layer. It is also observed in cross-sectional TEM that the number of through dislocations is smaller for the sample with this novel buffer layer and most threading dislocations are confined to below the buffer layer after TCA, which is in good agreement with the PL result. We tentatively attribute the origin of this improvement of the GaAs/Si epilayer to an increased concentration of Ga vacancies which will migrate and relieve the tensile stress.

The fabrication, properties and microstructure of Cu–Ag and Cu–Nb composite conductors

Abstract The properties and the microstructure of cold-drawn Cu–Ag and Cu–Nb composites have been investigated for their potential use as conductors in pulsed high field magnets. Cu–Nb and Cu–Ag are among the leading candidates for the 100T magnet to be built in cooperation between NHMFL and LANL. These conductors show a combination of high conductivity, high strength, adequate workability, and the final section size obtainable for the wire. The conductors are operated in the temperature range from liquid nitrogen to room temperature, and therefore the mechanical and electrical properties were measured at both −196 and +25°C. The 100T magnet requires conductors with various cross-sections. The conductors with small cross-sectional areas (6–12 mm 2 ) require higher strength. Thus, Cu–Nb composites with cross-sectional areas between 6 and 12 mm 2 were fabricated by bundling-and-drawing and characterized. The Cu–Ag composite was developed as one of the candidates for large cross-section applications. It was produced by casting, forging, rolling and cold drawing to a final cross-section of up to 45 mm 2 . In addition to the ability to fabricate coils for the magnet, we have considered the service life of the materials in regard to both cyclic loading and thermal fatigue. Examination of the initial portion of the stress–strain curve of cold-worked materials reveals that the internal stresses developed during the fabrication influence the mechanical response of the materials. Thus the properties of the drawn materials have been monitored as a function of cyclic loading and thermal annealing cycles. An important aspect of the selection of materials for high field magnets is the ability to obtain the material in large cross-sections and thus the work in this paper is concerned with the development of suitable production routes as well as the relationship between the structure and the properties of processed composites.

High responsitivity near infrared Ge photodetectors integrated on Si

The authors have fabricated and tested heterojunction Ge/Si photodetectors based on pure Ge epitaxially grown on Si (001) using a two-step UHV-CVD process followed by cyclic thermal annealing. The detectors exhibit responsivities as high as 550 mA/W at 1.32 µm and 250 mA/W at 1.55 µm and response times shorter than 850 ps.

Germanium Photodetectors for Silicon Microphotonics by Direct Epitaxy on Silicon

AbstractWe have grown high-quality Ge epilayers on Si using two-step ultrahigh vacuum/chemical-vapor-deposition followed by post-growth cyclic thermal annealing. Cyclic annealing was effective in reducing threading dislocation densities. The annealing process was improved by optimizing the dislocation velocity. We fabricated and tested metal-semiconductor-metal planar photodetectors using Ge epilayers grown on Si. Our measurement showed an improvement in the photodetector performance as a result of the improved materials quality. The process described in this paper for making high-quality Ge on Si is uncomplicated and can be easily integrated with Si CMOS processes.

Dielectric Properties of Highly Oriented Lead Zirconium Titanate Thin Films Prepared by Reactive RF-Sputtering

AbstractHighly (100) and (111) oriented lead zirconium titanate (PZT) thin films have been grown by using reactive rf-sputtering. PZT thin films with rhombohedral composition have been grown in different orientations using selective rapid thermal annealing cycles. The polarization versus electric field curves and the resistivity of the films were measured using a standardized RT66A ferroelectric test system. The dielectric constant and the loss were determined using an impedence analyzer. The PZT(100) oriented films showed larger dielectric constant and loss than the PZT(111) films. The PZT(100) films possessed sharper square-like hysteresis loops compared to the PZT(111) films, as expected from our phenomenological calculations.

Reduction of threading dislocations by InGaAs interlayer in GaAs layers grown on Si substrates

High-quality GaAs epilayers with dislocation densities of 1.2×106 cm−2 on (100)Si substrates have been obtained by insertion of an InGaAs strained interlayer combined with thermal cycle annealing instead of strained layer superlattices. All the layers were grown by low-pressure metalorganic vapor phase epitaxy. The threading dislocation density near the surface of 4 μm thick GaAs was measured by plan-view transmission electron microscopy. The threading dislocation density was found to be very sensitive to the In composition of the interlayer and the specifics of thermal cycle annealing.

MEMS-BASED SCANNING CALORIMETER FOR THERMODYNAMIC PROPERTIES OF NANOSTRUCTURES

Thermodynamic properties of small structures, such as the melting points and the process of mass transport, can be considerably different compared to material in the bulk form. Calorimetry is the standard experimental technique used to measure thermodynamics properties. However, this technique is extremely difficult to use for the study of small structures because the amount of energy exchanged during the measurement is extremely small - proportional to the amount of material. In order to measure small amounts of thermal energy we have scaled down the physical size of the calorimeter using MEMS technology. This thin-film differential scanning calorimeter has extremely high sensitivity, 0.01 mJ cm2, and is capable of measuring the melting phenomenon of 1 A of Sn deposited onto a SiN surface. In this article we investigate the size dependence of both the melting point and the heat of fusion for ultrathin films of Sn nanonstructures using multiple evaporation and thermal annealing cycles.

Heteroepitaxial Growth of InGaP on Si with InGaP/GaP Step-graded Buffer Layers

Heteroepitaxial growth of indium gallium phosphide (In1-xGaxP) with x ∼0.7 was successfully achieved on a silicon (Si) substrate by introducing step-graded buffer layers which consist of a gallium phosphide (GaP) buffer layer and In1-xGaxP layers whose gallium (Ga) composition x decreases in steps toward the direction of the growth. For the GaP buffer layer, the effects of thermal cycle annealing (TCA) were studied using a Rutherford back scattering channeling (RBS-C) measurement. The layer was shown to be improved greatly and a high-quality heteroepitaxial GaP layer could be obtained in the region close to the surface by introducing TCA. For the In1-xGaxP step-graded layers, the lattice strain, investigated using X-ray diffraction, was shown to be more relaxed using a Si substrate than using a GaP substrate. The growth of InGaP on a Si substrate with the step-graded layers is an effective method to reduce the strain in the InGaP layer.

Effect of In Situ Thermal Cycle Annealing on GaN Film Properties Grown on (001) and (111) GaAs, and Sapphire Substrates

The effect of in-situ thermal cycle annealing (TCA) has been investigated for GaN growth on GaAs(lOO), GaAs(111) and sapphire substrates. X-ray diffractometry (XRD) and surface morphology studies were performed for this purpose. Enhanced cubic phase characteristics were observed by employing annealingfor GaN layers grown on (001) GaAs. The thickness of the layer subject to annealing is critical in determining the phase of the subsequently grown layer. Thin initial layers appear to permit maintenance of the cubic phase characteristics shown by the substrate, while hexagonal phase characteristics are manifested for thick initial layers. Higher temperature of annealing of thick pre-annealed layers results in changes from mixed cubic/hexagonal phase to pure hexagonal phase. Growth on GaAs(111) substrates showed single cubic phase characteristics and similar enhancement of crystal quality by using TCA as for layers on GaAs(OOl). Micro-cracks were found to be present after TCA on GaAs(lll) substrates. Thermal cycling also appears to be beneficial for layers grown on sapphire substrates.

MOCVD growth of high-quality AlGaAs on Si substrates for high-efficiency solar cells

The crystallinity and solar cell efficiency of Al0.22Ga0.78As layers grown on Si substrates have been studied by varying the thermal cycle annealing (TCA) temperature. The optimum TCA temperature to obtain an Al0.22Ga0.78As layer with long minority carrier lifetime and high conversion efficiency has been presented. The active-area conversion efficiency of an Al0.22Ga0.78As solar cell on a Si substrate as high as 10.2% has been obtained under AM0 and 1 sun conditions.