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Measured emissivity as a function of temperature for samples with different thickness of SiO 2 coating on silicon at 1.53 m.
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The results of an ongoing collaborative project between the New
Jersey Institute of Technology (NJIT) and SEMATECH on the
temperature-dependent emissivity of silicon-related materials and
structures are presented in this study. These results have been acquired
using a spectral emissometer. This emissometer consists of a Fourier
Transform Infra-Red...
Context in source publication
Context 1
... of Christiansen filters [23]. The effect of oxide layer on silicon is to reduce the transmit- tance significantly. As the oxide thickness is increased, the transmittance decreases even further. Our results of correlating emissivity with temperature for SiO /Si as function of oxide thickness are summarized for one particular wavelength of m in Fig. 8. The emissivity of SiO /Si is as shown in this figure. These results of emissivity are plotted as function of oxide thickness for four specific temperatures at m in Fig. 9. As can be seen in this figure, the emissivity initially increases with oxide thickness and subsequently decreases. The oxide thickness corresponding to this ...
Citations
... Thickness of Si and SiO 2 are provided by the Si wafer manufacturer. According to literature, the average emissivity of SiO 2 with around 300 nm thickness on Si substrate is around 0.6 in the region of 1∼10 µm within the temperature of 200°C [26,27]. Therefore, all the exposed surfaces of SiO 2 are set with the emissivity of 0.6 in the radiation heat transfer module. ...
... h and ε have only to be on the surfaces in contact with air, and their value are based on literature, material library, or measured data. In this paper, h is defined as described above by the equivalent parameter h eq and ε is refer to literatures [26,27]. ...
Strong demand for developing the photothermal (PT) and electrothermal devices with ultra-large array is increasing. Thermal performance prediction is vital to optimize the key properties of the devices with ultra-large array. Finite element method (FEM) provides a powerful numerical approach for solving complex thermophysics issues. However, for calculating the performance of devices with ultra-large array, it is very memory-consuming and time-consuming to build an equal scale three-dimensional (3D) FEM model. For an ultra-large periodic array irradiated with a local heating source, the use of periodic boundary conditions could lead to considerable errors. To solve this problem, a linear extrapolation method based on multiple equiproportional models (LEM-MEM) is proposed in this paper. The proposed method builds several reduced-size FEM models to carry out simulation and extrapolation, which avoids dealing with the ultra-large arrays directly and greatly reduces the computation consumption. To verify the accuracy of LEM-MEM, a PT transducer with beyond 4000 × 4000 pixels is proposed, fabricated, tested and compared with the prediction results. Four different pixel patterns are designed and fabricated to test their steady thermal properties. The experimental results demonstrate that LEM-MEM has great predictability, and the maximum percentage error of average temperature is within 5.22% in four different pixel patterns. In addition, the measured response time of the proposed PT transducer is within 2 ms. The proposed LEM-MEM not only provides design guidance for optimizing PT transducers, but is also very useful for other thermal engineering problems in ultra-large array that requires facile and efficient prediction strategy.
... Due to reduced thermal conduction along the thermal bridge arms, the radiative heat coupling is also critical in the performance of state of the art bolometers [57,58]. As a result, the radiative heat transfer from the top and bottom surfaces of the pixel and supporting legs and substrate were also included, using an emissivity of 0.7, equal to that of silicon, for both PS and a-Si [59,60]. Fig. 12 shows the transient heating curve of the pixel resulted from a 100 nW step of heat applied to the membrane. ...
... This observation is strengthened by evidence of a dramatic rise in semiconductor's sub-bandgap emissivity at elevated temperatures. [13][14][15] A thermodynamic limit on the amount of this sub-bandgap radiation is placed by minimizing the process's entropy production. We thus arrive at a unified formulation of a PV process that can uphold its DB constraint in addition to thermodynamics' first and second laws. ...
... 2 In particular, we note the observed significant variations in the sub-bandgap emissivity of heated semiconductors, up to the point where practically a black-body source is being observed. [13][14][15] We are thus led to study a PV system with non-zero sub-bandgap emissivity/absorptivity. Since the generation of electron-hole pairs cannot be affected by sub-bandgap processes, the only modification is to the EB constraint, which now reads: ...
... Finally, ε sbg shows a similar trend as the temperature, in agreement with the known behavior of semiconductors at elevated temperatures. [13][14][15] However, unlike these past studies, here, the thermodynamic limit of this property, ε sbg , is one of the system's variables, just like T and V , rather than being an external parameter. For the most part, however, the value of ε sbg is negligible unless high concentrations or low thermal conductivities are encountered -a known heuristic fact. ...
The efficiency of a photovoltaic converter (solar cell) illuminated by a thermal source (sun) is commonly determined with Shockley and Queisser’s approach. The strength of this approach lies in its simplicity: All one needs to know is the solar cell’s bandgap, and the efficiency emerges from a detailed balance equation of the electron-hole pair generation and depletion rates at a given temperature. This article studies a single junction cell in outer space to show that a detailed balance approach is not always thermodynamically compatible. We then show that this inconstancy resolves once the cell’s sub-bandgap emission and absorption are included in its energy balance. Generalizing this result, we propose a unified formulation for a photovoltaic process that maintains its detailed balance constraints while not giving away thermodynamics’ first and second laws at all times and under any circumstances. Most importantly, our unified model allows heat conduction consideration to enter the photovoltaic analysis. Therefore, the proposed approach is critical for a single-junction cell and every photovoltaic process with an ample radiative power supply or limited conduction of heat such as concentrated space solar, thermo-photovoltaics thermoradiative, and thermophotonics power schemes.
... where T w is wall temperature of the reactor, ρ s is density of the substrate, c p is heat capacity of the substrate, Q s is heat flux conveyed from plasma toward the substrate, ε is surface emissivity of the substrate (ε ~ 0.6 for Si [44]), σ SB = 5.67 × 10 −8 [W⋅m −2 ⋅K −4 ] is the Stephan-Boltzmann constant, and V s and A s are volume and surface area of the substrate. From Eq. 17, the maximum temperature of plasma immersed small substrate can be calculated as follows: where q = Q s /A s . ...
A comprehensive study of the reversed arc plasma enhanced CVD (RACVD) reactor utilizing an Ar + H2 + CH4 plasma-creating mixture in the pressure range 1–100 Torr with a plasma flow direction opposite to the direction of the arc current was carried out. The reversed arc discharge has rising current–voltage characteristics showing voltage increasing with pressure and hydrogen concentration. The spectrum of the Ar-H2-CH4 plasma column includes CH, C2, and H2 molecular bands, in addition to Hα, Hβ, Hγ, and Hδ lines. The dissociation degree of H2 was estimated from the intensity ratio IHα/IArI of the Hα and ArI 750 nm lines using the optical actinometry method, yielding an average dissociation degree of hydrogen in the arc plasma of 15–20%. The average vibrational and rotational temperatures of CH radicals are Tv = Tr = 3000 K ± 300 K. The dissociation degree of hydrogen in the reversed arc discharge was calculated by the advection–diffusion-reaction model and showed reasonably good agreement both with experimental findings and with LTE calculations. The high concentration of nascent hydrogen and hydrocarbon radicals in the reversed arc plasma and its uniform distribution across the arc column makes it suitable for diamond coatings. The results obtained on the interaction of reversed arc plasma with substrates suspended within the current-carrier arc plasma column were applied to the description of a dusty reversed arc plasma in fluidized bed reactors. It was found that the energy effectiveness of the treatment of nanoparticles in the RACVD fluidized bed reactor exceeds 90%.
... Out of the three, only the emissivity has not yet been considered as an independent variable by either the DB or the thermodynamic approaches. We have also surveyed papers dealing with the measured emissivity of semiconductors, which showed that the subbandgap emissivity rises and the bandgap somewhat narrows at elevated temperatures [22][23][24][25][26] . Out of the two, the rise in emissivity seemed more pronounced. ...
Thermodynamics is accepted as a universal truth, encompassing all macroscopic objects. Therefore, it is surprising to find that, within our current understanding, the photovoltaic effect has so far eluded the first and second laws of thermodynamics. The inconsistency emerges from the fact that photovoltaics obey a distinct law of detailed balance1. Since radiative processes depend on only two independent variables that are the chemical potential and the temperature, the detailed balance, and the two laws of thermodynamics cannot be mutually solved. In this work, we resolve this incompatibility by proposing that the system is controlled by yet a third independent variable, which is related to the emissivity. This unification not only advances our fundamental understanding of light-matter interactions but, perhaps more importantly, allows us to assess the limiting factors of advanced photovoltaic concepts designed for elevated temperatures. These include thermophotovoltaics2, thermoradiative and thermophotonic solar power conversion, and radiative cooling, which are instrumental in our ability to develop advanced renewable energy technologies.
... The absolute values of calculated temperatures depend on the emissivity value (ε) of the wafer. The case discussed in Fig. 4a was calculated for ε Si ¼ 0.7, in agreement with reported data for Si at this temperature range (Ravindra et al. 1998). Further verification of the accuracy of temperature modeling was provided by studying the Laser-RTA of InP wafers. ...
© Springer Nature Switzerland AG 2020
K. Sugioka (ed.), Handbook of Laser Micro- and Nano-Engineering,
https://doi.org/10.1007/978-3-319-69537-2_29-1
The continuous progress in advancing thin films growth methods has enabled fabrication of innovative devices based on semiconductor microstructures. The epitaxial growth techniques, such as molecular beam epitaxy, chemical beam epitaxy, metal-organic chemical vapor deposition, and numerous derivatives of these techniques have made the films and microstructures based on Si, Si/SiGe, GaAs. GaAs/AlGaAs and other group IV-IV, III-V, II-V, and II-VI semiconductors readily available for research and commercial applications. Nevertheless, the output of these techniques has frequently proven limited when considering fabrication of microstructures with interfaces controlled at the atomic level, the integration of different bandgap materials within the same wafer or fabrication of microstructures having arbitrary profiles of their bandgaps either in the plane of the growth or in the direction of the growth. Some of these challenging problems have been resolved by taking advantage of the technology of infrared (IR) and ultraviolet (UV) which allowed delivering microstructures with characteristicsunattainable with conventional methods of fabrication. This chapter provides a review of the laser-based methods for fabrication of quantum semiconductor microstructures with bandgap engineered at the atomic level. The discussion involves bandgap engineering by pulsed laser deposition and quantum well/quantum dot intermixing techniques employing IR and UV lasers for the general area of application concerning monolithically integrated photonic devices.
... Directly measuring the peak temperature underneath the tool was difficult because of the interaction between the tool and top surface of the material during FSSP. In this study, the temperature profile at the near edge of the silicon nitride tool on the steel surface was measured by an IR camera in Figure 3a, because emissivity of the silicon nitride was close to 1 within a wide range of temperatures [29]. Figure 3a shows an example of snapshot image during FSSP with condition C (i.e., the 1800 rpm case). ...
Friction stir processing is a novel solid-state process to modify microstructures and their properties by intense, localized plastic deformation. However, little research has been reported for microstructure evolutions of advanced high-strength steels during the process. The present work focuses on the study of transient microstructure changes and local mechanical properties for friction stir spot processed dual-phase (DP) 980 MPa grade steel (DP980) under different peak temperatures. A pinless silicon nitride ceramic tool was used to produce relatively simple material deformation and flow near the tool. Friction stir spot processed steel samples were characterized by optical and electron microscopies. Furthermore, Vickers microhardness and nano-indentation measurements were used to study local mechanical properties for correlation with microstructures. A swallow layer of refined grains (<0.6 µm) was obtained with a low peak temperature (under 400 °C), whereas higher peak temperatures (>Ac1) led to a change in grain size with different microstructures (fine-grained DP or martensite). Electron back-scattered diffraction characterizations revealed a large deformation in the as-received microstructures (mixture of ferrite and tempered martensite) induced by friction stir spot processing, leading to recrystallization and grain refinement around the stirred zone. Also, nano-indentation measurements showed a higher hardness than the hardness of the as-received DP980. Friction stir processing with different process conditions effectively changed microstructures and local mechanical properties.
... The absolute values of calculated temperatures depend on the emissivity value (ε) of the wafer. The case discussed in Fig. 4a was calculated for ε Si ¼ 0.7, in agreement with reported data for Si at this temperature range (Ravindra et al. 1998). Further verification of the accuracy of temperature modeling was provided by studying the Laser-RTA of InP wafers. ...
The continuous progress in advancing thin films growth methods has enabled fabrication of innovative devices based on semiconductor microstructures. The epitaxial growth techniques, such as molecular beam epitaxy, chemical beam epitaxy, metal-organic chemical vapor deposition and numerous derivatives of these techniques have made the films and microstructures based on Si, Si/SiGe, GaAs. GaAs/AlGaAs and other group IV-IV, III-V and II-V and II-VI semiconductors readily available for research and commercial applications. Nevertheless, the output of these techniques has frequently proven limited when considering fabrication of microstructures with interfaces controlled at the atomic level, the integration of different bandgap materials within the same wafer or fabrication of microstructures having arbitrary profiles of their bandgaps either in the plane of the growth or in the direction of the growth. Some of these challenging problems have been resolved by taking advantage of infrared (IR) and ultraviolet (UV) technologies which allowed delivering microstructures with characteristics unattainable with conventional methods of fabrication. This chapter provides a review of the laser-based methods for fabrication of quantum semiconductor microstructures with bandgap engineered at the atomic level. The discussion involves bandgap engineering by pulsed laser deposition and quantum well/quantum dot intermixing techniques employing IR and UV lasers for the general area of application concerning monolithically integrated photonic devices.
... Previous studies have illustrated that the optical properties and the surface absorptivity of W are temperature-dependent [34][35][36][37]. One experimental study [35] showed that the n value of W significantly increases with temperature at near-infrared wavelengths, and nearly doubles at 2 µm when the temperature is raised from 300 K to 1500 K. Compared to W, Si 3 N 4 has a much lesser dependence of surface absorptivity with temperature, especially below wavelengths less than 8 µm [38]. Bhatt et al. [39] investigated the temperature-dependency of the spectral absorptivity of the Si 3 N 4 /W/Si 3 N 4 selective emitter using both simulation and experimental methods. ...
This paper presents a detailed-balance analysis required for the achievement of a high-efficiency spectral selective STPV system utilizing thermodynamic and optical modeling approaches. Key parameters affecting the design and optimization of spectrally selective surfaces that are essential for high-efficiency STPV applications are investigated. A complete GaSb-based planar STPV system utilizing a micro-textured absorber and a nanostructure multilayer metal-dielectric coated selective emitter was fabricated and evaluated. The micro-textured absorber features more than 90% absorbance at visible and near-infrared wavelengths. The selective emitter, consisting of two nanolayer coatings of silicon nitride (Si3N4) and a layer of W in between, exhibits high spectral emissivity at wavelengths matching the spectral response of the GaSb cells. The performance of the STPV system was evaluated using a high-power laser diode as a simulated source of concentrated incident radiation. When operated at 1670 K, an output power density of 1.75 W/cm² and a system efficiency of 8.6% were recorded. This system efficiency is higher than those of previously reported experimental STPV systems. Optical and thermal losses that occurred at multiple stages of the energy transport process were modeled and quantified. Essential guidelines to mitigate these losses and further enhance the system performance are also provided.
... One such example is using the measured or modeled spectral emissivity of the selective emitter at room temperature for estimating the thermal emission at higher temperatures. Previous studies [18][19][20][21][22] have reported that the optical constants of the refractory metals and the dielectric thin film layers vary with temperature. The deviation of the optical properties at the TPV operating temperature may have a direct Research Article impact on the surface spectral characteristics of the design, hence impacting the overall thermal-to-electric conversion efficiency. ...
... The same study also reported a significant increase in the NIR spectral emissivity of a tungsten grating structure at higher temperatures. In our study, the n and k values of W at 1500 K are derived from Barnes's work [18] and are used to simulate the reflectance spectra of the Si 3 N 4 /W/Si 3 N 4 stack at 1500 K. Similarly, another experimental study [19] showed that the temperature dependency of the n value and emissivity of Si 3 N 4 is minimal below 8 µm at ∼1100 K. As such, no change in the n values of Si 3 N 4 is incorporated in the simulation at high temperatures. ...
Spectral emissivity control is paramount for designing a high-efficiency selective emitter surface required for thermophotovoltaic (TPV) applications. Owing to the temperature dependency of materials optical constants, the spectral properties of a selective emitter surface changes with the emitter temperature. This paper presents the fabrication of a multilayer metal-dielectric ( ${\rm Si}_{3}{\rm N}_{4}/\rm W/Si_{3}{\rm N_{4}}$ S i 3 N 4 / W / S i 3 N 4 ) coated tungsten selective emitter aimed for GaSb-based TPV systems and studies the dependence of its surface spectral emissivity, $\varepsilon (\lambda)$ ε ( λ ) , upon a temperature ranging from 300 K to 1500 K. Both the simulation and experimental methods were used to characterize $\varepsilon (\lambda)$ ε ( λ ) as a function of temperature. For wavelengths less than 1.4 µm, $\varepsilon (\lambda)$ ε ( λ ) was found to have a minimal dependence on temperature. Beyond 1.4 µm, $\varepsilon (\lambda)$ ε ( λ ) increases with the temperature. At 1.55 µm, the simulation and experimental data estimated a ${\sim}{{4}}\%$ ∼ 4 % greater emissivity at 1500 K than at room temperature. At 1500 K, the increased $\varepsilon (\lambda)$ ε ( λ ) at longer wavelengths lowered the spectral conversion efficiency of the selective emitter from 58% to 47%. The output power density, sub-bandgap loss, and TPV conversion efficiency ( ${\eta _{\rm TPV}}$ η T P V ) for a GaSb cell illuminated by the selective thermal emitter at 1500 K were estimated. ${\eta _{\rm TPV}}$ η T P V drops from 13.7% to 11% due to the increased sub-bandgap emission at 1500 K. Essential approaches for mitigating the sub-bandgap losses to further improve ${\eta _{\rm TPV}}$ η T P V are also discussed.
