SiGe Thin Films Research Articles

Influence of annealing on Si-Ge thin films with high concentration of tellurium and zinc

Influence of annealing on Si-Ge thin films with high concentration of tellurium and zinc

Enhancing the Responsiveness of Thermoelectric Gas Sensors with Boron-Doped and Thermally Annealed SiGe Thin Films via Low-Pressure Chemical Vapor Deposition.

Thermoelectric gas sensor (THGS) devices with catalysts and Si0.8Ge0.2 thin films of different boron doping levels of 1018, 1019, and 1020 cm-3 were fabricated, and their transport properties are investigated. SiGe films were deposited on Si3N4/SiO2 multilayers on Si substrates using low-pressure chemical vapor deposition (LPCVD) and thermally annealed at 1050 °C. The Seebeck coefficients of the SiGe films were increased after thermal annealing, ranging from 191 to 275 μV/K at temperatures of 74 to 468 °C in air, and reaching the highest power factor of 6.78 × 10-4 W/mK2 at 468 °C. The thermal conductivity of the SiGe films varied from 2.4 to 3.0 W/mK at 25 °C. The THGS detection performance was tested for the H2 gas in air from 0.01 to 1.0%, and compared to the thermoelectric properties of the SiGe films. The high-temperature annealing treatment process was successful in enhancing the thermoelectric performance of both the SiGe films and sensor devices, achieving the best THGS performance with the sensor device fabricated from the annealed SiGe film with 1018 cm-3 boron-doped Si0.8Ge0.2.

Heat transport evaluation of amorphous Si, SiGe, and Ge thin films using 3ω method and minimum heat conduction model

Heat transport evaluation of amorphous Si, SiGe, and Ge thin films using 3ω method and minimum heat conduction model

Organic-inorganic PTAA-SiGe transparent optical materials performance analysis for photo device applications

The SiGe materials has currently received a lot of interest due to its application for the advancement of optoelectronics and related sensor technologies. Its promising stability, and band gap-dependent performance for both bulk and nano-crystalline properties are vital as optical materials. To investigate the electrical performance of SiGe active materials based photo device, the spin coated organic p-materials contact is developed on sputtered SiGe on Quartz and ITO glass substrates. Both Si0.8Ge0.2 and Si0.9Ge0.1 films greater than 85 % visible band transparency are predicted that the deposited SiGe is nano-crystalline nature. It is also revealed from absorption-based band gap, AFM grain size and XRD analysis. The transmittance of SiGe thin film is increased with the microstrain of the films as a result, better opto-electrical performance is displayed. Ge composition though slightly makes variation of lattice constant and strain effect however, relatively lower transmittance films greater current density is exhibited. A higher rectifying ratio for lower transparent SiGe material deposited on ITO glass substrate is shown in the dark. Transparency and optoelectrical performance viewpoint white light illuminated PTAA/Si0.8Ge0.2 is shown better on Quartz substrate whereas the dark analysis PTAA/Si0.9Ge0.1 is realized more favorable on ITO glass substrate.

Efficiency enhancement in SiGe thin film solar cell by a CNT grating structure

In this paper, a new structure of SiGe thin film solar cell using a carbon nanotubes (CNT) grating layer is proposed. CNT grating layer is used which reduces the reflection loss from the surface and maximizing optical absorption in the active layer of the cell. In order to reduce the carrier recombination in the back contact, a GaAs back-surface field (BSF) layer was used. The simulation results show that the efficiency of the proposed structure is 29.32%. Furthermore, we were able to increase the efficiency to 31.3% by optimizing the structural parameters including the depth and number of grating periods.

Light scattering features induced by residual layers in dielectric dewetted nanoparticles

All-dielectric, sub-micrometric particles obtained through solid state dewetting of thin SiGe-films have been shown to support Mie resonances together with a high-quality monocrystalline composition and atomically smooth facets. Recently, a precise study on the impact given by the effective complex morphology of a SiGe dewetted nanoparticle to the Mie scattering properties has been provided and carried on through a novel experimental technique called Dark-field Scanning Optical Microscopy. In this work, by means of the same experimental technique and numerical simulations of light scattering, we show how the presence of a pedestal enriched with silicon placed under the SiGe-nanoparticle results in a sharp peak at high energy in the total scattering cross-section. Exploiting a tilted illumination to redirect scattered light, we are able to discriminate the spatial localization of the pedestal-induced resonance. Our results contribute to extending the practical implementations of dewetted Mie resonators in the field of light scattering directionality, sensing applications and show further engineering options beyond the simple isolated-island case.

Hybridization of ellipsometry and XPS energy loss: Robust band gap and broadband optical constants determination of SiGe, HfON and MoOx thin films

In this study, we compare the robustness of optical constants and optical band gap determination of three different materials: SiGe, N-doped HfO2 and MoOx, using the combination of two techniques: spectroscopic ellipsometry, and energy loss signal (ELS) of X-ray photoelectron spectroscopy (XPS). The determination of such physical properties is achieved through the hybridization of the two techniques based on multiple Tauc-Lorentz model, applied on the whole energy range of measurement.Such use of hybridized data demonstrates a new robust method to determine the band gap of the studied materials, together with the optical indices (refractive index and extinction coefficient) on a wide energy range (up to 40 eV). This method provides an extension of determination of the relevant physical quantities compared to each technique on their own.Moreover, this algorithm is tested on limit conditions, where the energy ranges of measurement of the two respective techniques presented no overlap. Yet the use of a unique physical model still allows us to calculate the different physical quantities even on the energy range where no measurement is performed, validating the semi-predictive nature of the hybrid technique. Additional measurements under different experimental configurations validate the extended scope of such hybrid technique.

Thermoelectric transport properties of Si, SiGe, and silicide CMOS-compatible thin films.

Characterization of thermoelectric transport properties for temperature sensing, cooling, and energy harvesting applications is necessary for a reliable device performance in progressively minimized computer chips. In this contribution, we present a fully automated thermovoltage and sheet resistance measurement setup, which is calibrated and tested for the production of silicon- and silicon-germanium-doped as well as silicide complementary metal-oxide-semiconductor-compatible thin films. A LabVIEW-programmed software application automatically controls the measurement and recording of thermovoltages at individually defined temperature set points. The setup maps average temperature and temperature differences simultaneously in the regime from 40 to 70 °C. The Seebeck coefficient calculated by means of the inversion method was used to eliminate the offset voltage influence. Finally, we present and discuss the Seebeck coefficient as well as the sheet resistance for application-specific different temperature set points of several doped poly-Si, poly-SiGe, and silicides.

Effect of nanostructuring on thermoelectric performance of SiGe thin films

We experimentally investigated the effect of nanostructuring on the thermoelectric performance of SiGe thin films. Nanoscale porous structures were fabricated using lithography in a top-down approach to reduce the thermal conductivity of the thin films and the thermoelectric figure of merit (ZT) was evaluated. The thermal conductivity of nanostructured SiGe thin films is up to 24% lower than that of thin film without nanostructure while the electrical conductivity is up to about 19% lower, resulting in a 4% increase in ZT value to 0.041 at RT. Since the mean free path (MFP) of phonons in SiGe is short compared to the characteristic length of the nanostructures, the effect of nanostructuring on thermoelectric performance is limited. Nanostructuring is known as a promising method to increase ZT values. However, it is only effective when the thermal phonon MFPs are comparable to the characteristic length of the nanostructure.

Composition Dependence Structural and Optical Properties of Silicon Germanium (SiχGe1−χ) Thin Films

This study investigates the structural and optical characteristics of Silicon Germanium (SiGe) thin films with varying compositions and annealing temperatures for potential use in electronic and optoelectronic devices. Si0.8Ge0.2 and Si0.9Ge0.1 films were deposited onto a high-temperature quartz substrate and annealed at 600 °C, 700 °C, and 800 °C before being evaluated using an X-Ray Diffractometer (XRD), Atomic Force Microscopy (AFM), and a UV-Vis Spectrometer for structural and optical properties. The results show that increasing the annealing temperature results in an increase in crystalline size for both compositions. The transmittance for Si0.8Ge0.2 decreases slightly with increasing temperature, while Si0.9Ge0.1 remains constant. The optical band gap for Si0.9Ge0.1 thin film is 5.43 eV at 800 °C, while Si0.8Ge0.2 thin film is 5.6 eV at the same annealing temperature. XRD data and surface analysis reveal significant differences between the band edges of SiGe nano-structure materials and bulk crystals. However, the possibility of a SiGe nano-crystal large band gap requires further investigation based on our study and related research works.

Self-formation of SiGe oxide, Ge, and void multilayers via thermal oxidation of hydrogenated epitaxial SiGe films

In this work, hydrogenated SiGe thin films epitaxially grown on crystalline Si (c-Si) at 175 °C are annealed at 800 °C in a low vacuum system. The influence of H from the thin film and residual O atoms in the vacuum system on the structural changes of SiGe is presented. Multilayers consisting of c-Si/SiGe/void/Ge/SiOx/SiGeOx are obtained by taking advantage of the hydrogen present in the epitaxial SiGe layer. Various annealing conditions are applied to study the evolution of SiGe layers. The surface morphology, crystallinity, composition and micro structure of the multilayer stack formed during the annealing process are investigated in detail. A discussion based on the diffusion of H and O atoms is presented to account for this extraordinary process.

Evaluation of Temperature Variation in the Debye-Waller Factor for Single Crystalline Bulk Silicon Germanium by XAFS

1. Background and purpose Silicon germanium (SiGe) is expected as a next-generation electronic and thermoelectric device materials because of its higher carrier mobility than Si and lower thermal conductivity than Si and Ge. Therefore, it is important to understand the carrier scattering and phonon transport properties in order to apply SiGe as a device. We have reported that the atomic vibration in Si-rich SiGe thin films on Si substrates may be suppressed by the lattice strain, based on X-ray absorption fine structure (XAFS) measurements [1]. In this study, we demonstrated XAFS spectra of strain-free single crystalline bulk SiGe and estimated the Einstein temperature (T E) which characterizes phonons, to investigate the influence of Ge fraction and lattice strain in SiGe at nanoscale. 2. Experimental method Strain-free single crystalline bulk SiGe were grown by the traveling liquidus zone method with Ge fractions of 32 and 45 % [2]. We measured the XAFS spectra of the Ge-K absorption edge for the bulk SiGe in the transmission mode at BL14B2 in the SPring-8 synchrotron facility. We also measured a single crystalline bulk Ge as a reference sample. The sample temperature was controlled between 10 - 600 K using a refrigerator or a heating cell during measurements. Then, we extracted the EXAFS oscillations from the obtained XAFS spectra in order to investigate the temperature variation of the Debye-Waller factor. 3. Results and discussion Figure 1 shows the temperature dependence of the change in the Debye-Waller factor with reference to 10 K (Δσ 2) for Ge, SiGe thin films, and bulk SiGe. From Fig. 1, the change in Δσ 2 with temperature is slower for SiGe than for Ge. The effect of Ge fraction on the change in Δσ 2 is negligible. Further, the changes in Δσ 2 with temperature for SiGe were similar regardless of the lattice strain. Therefore, it is confirmed that the Ge fraction and the lattice strain in SiGe have little effect on the atomic vibration.Here, since σ 2 is expressed by Eq. (1) [3], Δσ 2 can be expressed as Eq. (2), where T is the absolute temperature, σ s 2 is the static Debye-Waller factor, A is a constant, and T E is the Einstein temperature. σ 2(T) = σ s 2 + Acoth(T E / 2T), (1)Δσ 2(T) = A[coth(T E / 2T) – coth{T E / (2 × 10)}], (2)The relationship between T E and the Ge fraction obtained from Eq. (2) is shown in Fig. 2. Figure. 2 indicates that T E decreases with increasing Ge fraction in Si-rich SiGe, suggesting that phonons are easily excited in SiGe with a high Ge fraction. Thus, it is considered that the effect of Ge fraction on atomic vibration in SiGe is much larger than their inner strains. 4. Acknowledgment The XAFS measurements were performed at BL14B2 in SPring-8, approved by JASRI, under proposal numbers 2019A1773, 2019B1802, and 2021A1661.

Structural, magnetic and Magneto-transport properties of Mn-doped SiGe thin films

Mn-doped polycrystalline SiGe thin films are fabricated by radio frequency magnetron sputtering and subsequent rapid thermal annealing. Structural characterizations show that the Mn atoms are distributed uniformly in the SiGe matrix and mainly occupy the substitutional sites with 2+ state. X-ray magnetic circular dichroism signals reveal the spin and orbital magnetic moment information of the samples. Magnetic measurements show that the Curie temperature is up to ∼ 290 K and the effective magnetic moment is about 1.57 μB/Mn. Magneto-transport measurements reveal anomalous Hall effect, another signal of ferromagnetism in the samples. Our results provide insights into the structure and the ferromagnetism of the Mn-doped SiGe thin films and may be useful for related spintronic applications.

Mn-doped SiGe thin films grown by UHV/CVD with room-temperature ferromagnetism and high hole mobility

In this work, silicon-germanium (SiGe) thin films are epitaxially grown on Ge substrates by ultra-high vacuum chemical vapor deposition and then doped with Mn element by ion-implantation and subsequent rapid thermal annealing (RTA). The characterizations show that the epitaxial SiGe thin films are single-crystalline with uniform tensile strain and then become polycrystalline after the ion implantation and following RTA. The magnetization measurements indicate that the annealed thin films exhibit Mn concentration-dependent ferromagnetism up to 309 K and the X-ray magnetic circular dichroism characterizations reveal the spin and orbital magnetic moments from the substitutional Mn element. To minimize the influence of anomalous Hall effect, magneto-transport measurements at a high magnetic field up to 31 T at 300 K are performed to obtain the hole mobility, which reaches a record-high value of ∼1230 cm2 V−1 s−1, owing to the crystalline quality and tensile strain-induced energy band modulation of the samples. The first demonstration of Mn-doped SiGe thin films with room-temperature ferromagnetism and high carrier mobility may pave the way for practical semiconductor spintronic applications.

Optimization of LPCVD phosphorous-doped SiGe thin films for CMOS-compatible thermoelectric applications

The incessant downscaling of building blocks for memory and logic in computer chips requires energy-efficient devices. Thermoelectric-based temperature sensing, cooling as well as energy harvesting could be useful methods to reach reliable device performance with stable operating temperatures. For these applications, complementary metal–oxide–semiconductor (CMOS)-compatible and application ready thin films are needed and have to be optimized. In this work, we investigate the power factor of different phosphorous-doped silicon germanium (SiGe) films fabricated in a 300 mm CMOS-compatible cleanroom. For the thermoelectric characterization, we used a custom-built setup to determine the Seebeck coefficient and sheet resistance. For sample preparation, we used low pressure chemical vapor deposition with in situ doping and subsequent rapid thermal annealing on 300 mm wafers. Thin film properties, such as film thickness (12–250 nm), elemental composition, crystallinity, and microstructure, are studied via spectroscopic ellipsometry, x-ray photoelectron spectroscopy, x-ray diffraction, atomic force microscopy, and TEM. The SiGe-based thin films vary in the ratio of Si to Ge to P and doping concentrations. A power factor of 0.52 mW/m K2 could be reached by doping variation. Our results show that SiGe is a very attractive CMOS-compatible material on the 300 mm wafer level and is immediately ready for production of thermoelectric embedded applications.

A review on single crystal and thin film Si–Ge alloy: growth and applications

Dual application of Si–Ge alloy in thermoelectric and BICMOS in the semiconductor industry.

Annealing Effect on Seebeck Coefficient of SiGe Thin Films Deposited on Quartz Substrate

Over the past few years, thermoelectrics have gained interest with regard to thermoelectricity interconversion. The improvement in the efficiency of the thermoelectric material at an ambient temperature is the main problem of research. In this work, silicon–germanium (SiGe) thin films, owing to superior properties such as nontoxicity, high stability, and their integrability with silicon technologies, were studied for thermoelectric applications. P-type SiGe thin films were deposited on quartz substrates by DC/RF magnetron sputtering and annealed at three different temperatures for 1 hour. Significant enhancement in the Seebeck coefficient was achieved for the sample annealed at 670 °C. A high power factor of 4.1 μWcm−1K−2 was obtained at room temperature.

Ion beam-assisted solid phase epitaxy of SiGe and its application for analog memristors

Low dimensional defects such as dislocation in single crystal Si are known to serve as a fast diffusion path of metal ions. Recently, many efforts have been made to employ dislocations in single crystal based oxide and silicon as reliable Ag filaments in CBRAM (Conductive Bridge Resistive Memory). In this study, we report the synthesis of the SiGe epitaxy thin films by an ion beam-assisted solid phase epitaxy process and its application for analog CBRAM memristors. The epitaxial SiGe thin films were produced by implanting Ge ions into a LPCVD a-Si film, followed by post annealing. We found that the interface oxide between a-Si and c-Si hinders facile epitaxy growth of a-Si. Thus, the ion implantation parameters were carefully adjusted to effectively remove the interface oxide and produce the epitaxy thin films of high quality. The low dimensional defects, identified to be a stacking fault by TEM observations, were observed to be densely located near the surface region of the SiGe epitaxy thin film. We fabricated the CBRAM devices by sandwiching the epitaxial Si thin films between an active metal electrode of Ag and a heavily doped Si wafer. We investigated the performances of the CBRAM devices and discuss the effect of the low dimensional defects on the switching behaviors of the devices. We found that the Ge implantation enables forming-free CBRAM operation and also provides reduced variations in set and reset voltages. Furthermore, we performed the feasibility study on the use of the epitaxial Si based CBRAM for artificial synapse for neuromorphic computing.

Growth of SiGe thin films with uniform and non-uniform Si concentration profiles on insulating substrates by high-speed continuous wave laser annealing

To realize next generation electronics and energy harvesting, crystal growth of silicon-germanium thin film on insulating substrate was investigated by high-speed continuous wave laser annealing. As a result, growth of polycrystalline (poly-) SiGe thin films on insulating substrate became possible. Furthermore, by tuning the laser annealing conditions, we have succeeded in controlling the Si concentration profiles after growth in a wide range from uniform to laterally graded distributions. These results and discussions will facilitate the development of next-generation electronics, and energy harvesting devices.

Novel method for the determination of the optical conductivity and dielectric constant of SiGe thin films using Kato-Adachi dispersion model

ABSTRACT In the present paper, we report a combined experimental and theoretical study of compositionally graded thin films grown on Si at 550°C. The study has been conducted for two particular values of the Ge fraction x namely x = 0.05 and x = 0.1. This choice finds its origin with the circumstance of getting good material quality by the obtention of totally relaxed layers with dislocation-free, as well as a good thermal conductivity of the active layer. The curves of optical constants and optical conductivity were performed by fitting the experimental ellipsometric spectra. Theoretical results reveal that the layers thickness of all studied samples was about 110 nm, suggesting the accuracy of the new Kato-Adachi spectroscopic ellipsometry model developed herein. Furthermore, current–voltage characteristic disclose that the efficiency of the structure corresponding to the fraction x = 0.1 is higher than the other solar cell due to higher values of Voc and FF.