-
[show abstract]
[hide abstract]
ABSTRACT: Amorphous Si-Ge-Au thin films exhibit high thermoelectric power. To understand the role of Au in the thermoelectric properties,
we studied the structural and thermoelectric properties of Si/Au and Ge/Au thin films. Samples were prepared by electron beam
evaporation. Au was found to have two important roles. One is as a carrier source. Therefore, Au composition influences thermoelectric
properties. The other role is that Au causes the crystallization of Si and Ge at lower temperature. The grain size ranged
from ten to a few tens of nanometers. We conclude that the fine structure is important for high thermoelectric performance.
KeywordsThermoelectric-SiGe-amorphous-thin film
Journal of Electronic Materials 04/2012; 39(9):1627-1633. · 1.47 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The amorphous Si-Ge-Au thin films show the extremely high thermoelectric properties. But reproducibility of the samples was not enough, because Au dopant was evaporated from dissolved Ge-Au ingot. In order to improve this problem, the thin film samples were deposited by ultra high vacuum evaporation system with three individual controlled sources, Si, Ge and Au. The samples were prepared of Si/Au/Ge/Au 4 layers as one period of 10 nm. And all the samples have 30 periods. Composition and thermoelectric properties of the samples were measured. The compositions of the thin films were measured by X-ray fluorescent analysis and that was consistent with intended value. The maximum value of thermoelectric power was ~10<sup>-3</sup> V/K at room temperature. By this sample preparation procedure, we have succeeded to make thin films with accurate dopant composition.
Thermoelectrics, 2007. ICT 2007. 26th International Conference on; 07/2007
-
[show abstract]
[hide abstract]
ABSTRACT: In this paper, we report the recrystallization process of Si-Ge-Au amorphous thin film with extremely large thermoelectric power that was prepared in ultra high vacuum. We observed the morphology of samples by using FE-SEM and FE-TEM. We found that the power factor increased at near room temperature for high Au concentration samples. But after several annealing cycles, segregations were observed on high Au concentration samples. The diameter reached 30 μm at maximum on 300 nm thickness thin film. These segregations were two types. One type was Au segregation and the other was Si-Ge segregation.
Thermoelectrics, 2005. ICT 2005. 24th International Conference on; 07/2005
-
[show abstract]
[hide abstract]
ABSTRACT: In order to disclose the important parameter from factors which affected to thermoelectric properties of the amorphous Si-Ge-Au thin films, annealing of samples were repeated with temperature range between room temperature and 1000 K. Electrical resistivity was stabilized in whole temperature range by only one thermal annealing cycle. On the other hand, thermoelectric power was not stabilized in whole temperature range even after several annealing cycles. Electrical resistivity and thermoelectric power of the amorphous Si-Ge-Au thin films could be affected by different parameters of amorphous structure such as dangling bonds, bond angle and interatomic distance. Further, improvement of the thermoelectric properties can be achieved with controlling the annealing temperature range and number of annealing cycle which affects to amorphous parameters.
Thermoelectrics, 2002. Proceedings ICT '02. Twenty-First International Conference on; 09/2002
-
[show abstract]
[hide abstract]
ABSTRACT: The control of thermoelectric properties is attempted by changing the, substrate temperature. Amorphous thin films were prepared by the alternate deposition of Si and Ge doped heavily with Au in ultrahigh vacuum chamber. The temperature dependence of electrical resistivity of the sample deposited at 600 K has unique characteristics. The power factor decreases as the substrate temperature increases. Electrical resistivity and thermoelectric power have different tendency for the substrate temperature. The power factor can be enhanced by controlling electrical resistivity and thermoelectric power independently at the optimum substrate temperature.
Thermoelectrics, 2002. Proceedings ICT '02. Twenty-First International Conference on; 09/2002
-
[show abstract]
[hide abstract]
ABSTRACT: We have been studied thermoelectric characteristics of Si/(Au-doped Ge) superlattice thin films at temperatures from room temperature (RT) to low temperatures less than 100 K and compared these to those of Si and (Au+Ge) alloy thin film. In the Si/(Ge+Au) superlattice after heating process the electric resistivity decreased at all temperature. This annealed Si/(Ge+Au) superlattice showed the high thermoelectric power of 105 μV/K at 290 K, compared with the unannealed Si/(Ge+Au) or the alloy film. At temperatures less than 200 K, however, the thermoelectric power of the unannealed Si/(Ge+Au) switched polarities from positive to negative and reached -4.6 mV/K at 80 K. This large negative thermoelectric power at low temperature was not observed in the annealed Si/(Ge+Au) or the alloy film. On the other hand, magnetic field characteristics of all samples showed no effect at 100 K, 200 K or 290 K. This was explained using the two-band parabolic model calculation, assuming that a large amount of Au-doping caused a very low carrier mobility.
Thermoelectrics, 2002. Proceedings ICT '02. Twenty-First International Conference on; 09/2002
-
[show abstract]
[hide abstract]
ABSTRACT: We intended to control the degree of amorphousness with the
substrate temperature. Amorphous thin films were prepared by the
alternate deposition of Ge, doped heavily with Au, and Si in an
ultrahigh vacuum chamber. In this paper, we compare the thermoelectric
properties of amorphous Si/Ge thin films deposited on the substrate at
77 K and room temperature. The power factor of the sample deposited on
the substrate at 77 K increases by the thermal annealing compared to
that of the sample deposited at room temperature
Thermoelectrics, 2001. Proceedings ICT 2001. XX International Conference on; 02/2001
-
[show abstract]
[hide abstract]
ABSTRACT: The noncontact imaging of the buried structures is carried out in the open-air atmosphere by using the photothermal deflection
(PTD) method. We applied these techniques to the layered samples. Besides the PTD images for the optically opaque buried structures,
the parameters of the materials such as thermal diffusivity can also be calculated from the PTD amplitude and phase signal
in the PTD scanning images. When the PTD signals at two different modulation frequencies are used, the thermal diffusivity
of the buried structure can be obtained from the PTD signal outside of the sample nondestructively.
Applied Physics A 08/1999; 69(3):343-346. · 1.63 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We have studied the thermoelectric properties of a SiC-based thermoelectric semiconductor with Ag and polysilastylene (PSS) as a dopant and as a sintering additive, respectively. Ag is an effective dopant to decrease the electrical resistivity of the SiC-based p-type thermoelectric semiconductor. It introduces carrier (hole) concentration 103−104 times larger than the case of Al-doped SiC with the typical doping concentration. PSS can control the sample density, which is one of the important factors in decreasing the electrical resistivity and thermal conductivity of the sintered samples. The figure of merit of the sample with Ag 2.0 wt% and PSS 0.1 wt% was estimated to reach 4 × 10−4 K−1 at 700 °C. This value implies that the SiC/Ag system is one of the promising thermoelectric materials for a high-temperature region.
Journal of Materials Research. 04/1999; 14(05):1752 - 1759.
-
[show abstract]
[hide abstract]
ABSTRACT: Silicon carbide is expected to be a hard thermoelectric material which can be used at high temperature. Recently, a low dimensional structure has been fabricated as new materials such as thin films. We made thin films of SiC by the evaporation technique with several metal dopants which are silver, nickel and copper. These dopants act as p-type acceptors and could reduce the resistance of SiC and raise the performance as thermoelectric materials. In the 5 wt.% Ag doped samples, the thermoelectric power is about 10 μV/K at 500°C and the temperature dependence of the thermoelectric power is weak in all samples. The thermoelectric power is smaller than that of the bulk samples with the same dopants for SiC/Cu and SiC/Ag, and larger for SiC/Ni. The electrical conductivity increases as temperature increases. SiC/Ag thin films have large conductivity compared with the bulk samples. In the SiC/Ni films, the conductivity is also enhanced and the thermoelectric properties are improved at high temperature
Thermoelectrics, 1998. Proceedings ICT 98. XVII International Conference on; 06/1998
-
[show abstract]
[hide abstract]
ABSTRACT: Silicon carbide is a wide gap semiconductor which is expected to
be used in the high temperature region. It has large electrical
resistivity and large thermal conductivity. These properties are not
favorable for thermoelectric devices. In this paper, Si and Ag were
selected as dopants to reduce the thermal conductivity and the
electrical resistivity, respectively. These dopants were effective in
improving the thermoelectric properties in our previous works. The
thermoelectric properties of SiC/Si/Ag have been studied over
temperatures ranging from room temperature to 750°C as a function of
both Si concentration (10.0 wt.%~40.0 wt.%) and Ag concentration (1.0
wt.%~4.0 wt.%). The thermal conductivity and the electrical resistivity
decreased with increasing temperature. The figure of merit Z approached
1.1×10<sup>-4</sup> K<sup>-1</sup> at around 750°C. We
conclude that Si with Ag doped SiC is a promising thermoelectric
material
Thermoelectrics, 1998. Proceedings ICT 98. XVII International Conference on; 06/1998
-
[show abstract]
[hide abstract]
ABSTRACT: The photoacoustic (PA) spectra are measured on Porous silicon (PS) which is a light emitting Si. PS has many pores and is constructed from the PS layer and the Si substrate. We analyze the PA spectra by the scattering model with the reflection at the interface between the PS layer and the substrate. The scattering effects, the reflection one and the effects of the layer structure on the PA signal are discussed. We compare this model to real PS samples. Two layer structure fits well with the wavelength dependence of PA spectra for the thin PS films
Ultrasonics Symposium, 1998. Proceedings., 1998 IEEE; 02/1998
-
[show abstract]
[hide abstract]
ABSTRACT: The thermoelectric properties of the p-type SiC:Ni sintered
thermoelectric semiconductor have been studied as functions of Ni
concentration (from 0.5 wt.96 to 5.0 wt.95) and temperature (from RT to
700°C). The electrical resistivity decreases drastically for all the
Ni concentration range compared with other dopants such as Cu, Al and B
at room temperature. The electrical resistivity and thermoelectric power
decrease with increasing temperature. The value of the figure of merit Z
approaches 1.4×10<sup>-4</sup> at around 700°C. The condition
of the doped impurity atom Ni has also been studied magnetically. It is
confirmed that Ni does not segregate in the SiC sintered sample. We
conclude that Ni is well diffused into SiC and it is one of the most
effective dopants for SiC-based thermoelectric materials
Thermoelectrics, 1997. Proceedings ICT '97. XVI International Conference on; 09/1997
-
[show abstract]
[hide abstract]
ABSTRACT: Differential isothermal capacitance transient spectroscopy (DICTS) and normalized isothermal capacitance transient spectroscopy (NICTS) were proposed to improve the resolution of the conventional isothermal capacitance transient spectroscopy (ICTS) which could characterize the deep levels in semiconductors isothermally. The resolution of the methods was studied for the closely spaced energy levels by the numerical simulation. Though the resolvable emission rate ratio R (R = λ2/λ1, where λ1 and λ2 are each thermal emission rate for two levels) of ICTS was around 5, R of DICTS was around 4. Moreover, R of NICTS reached 3.5 which is less than that of any other conventional methods. The error ratio of the estimation is almost the same as ICTS. The new method was applied to study the deep levels in a Si:Au system as an example and found two closely spaced energy levels explicitly. © 1997 American Institute of Physics.
Review of Scientific Instruments 04/1997; 68(5):2116-2120. · 1.37 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Deep-level transient spectroscopy (DLTS), which is widely used to characterize deep impurity centers in semiconductors, assumes a single exponential wave form for the transient junction capacitance. When there are several closely spaced energy levels this assumption is no more valid, and the conventional DLTS may lead to errorneous results. To overcome this difficulty we propose here a novel method which we call the multi-exponential DLTS(MEDLTS). The transient wave form of the junction capacitance is directly analysed into multi-exponential compouents using the nonlinear least-squares analysis program DISCRETE developed by Provencher. The resolved time constants of these components are then displayed in the form of aT
2–1/T plot. According to the results of simulation with various parameters MEDLTS is shown quite effective to resolve closely spaced energy levels which can not be resolved by the conventional DLTS. As an example of the application of this method deep levels in Si: Au were investigated. The results have shown that a single peak in conventional DLTS actually consists of two adjacent levels with activation energies and capture cross-sectionsE
B1=0.49 eV,
B1=1.110–14cm2 andE
B2=0.46 eV,
B2=1.310–15 cm2 and with amplitude ratio 11.
Applied Physics A 02/1986; 39(3):197-202. · 1.63 Impact Factor
