• JSTS:Journal of Semiconductor Technology and Science
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• v.16 no.6
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• pp.854-859
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• 2016

Recently, GeSn is drawing great deal of interests as one of the candidates for group-IV-driven optical interconnect for integration with the Si complementary metal-oxide-semiconductor (CMOS) owing to its pseudo-direct band structure and high electron and hole mobilities. However, the large lattice mismatch between GeSn and Si as well as the Sn segregation have been considered to be issues in preparing GeSn on Si. In this work, we deposit the GeSn films on Si by DC magnetron sputtering at a low temperature of $250^{\circ}C$ and characterize the thin films. To reduce the stresses by GeSn onto Si, Ge buffer deposited under different processing conditions were inserted between Si and GeSn. As the result, polycrystalline GeSn domains with Sn atomic fraction of 6.51% on Si were successfully obtained and it has been demonstrated that the Ge buffer layer deposited at a higher sputtering power can relax the stress induced by the large lattice mismatch between Si substrate and GeSn thin films.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.8
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• pp.643-650
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• 2000

Density-of-states effective mass(m*$_{d}$) and conductivity mass(m*$_{c}$)for Ge and Ge$_{0.8}$/Sn$_{0.2}$ are obtained by using 8$\times$8 k.p and strain Hamiltonians. It is shown that m*$_{d}$ and m*$_{c}$ for electrons in Ge/Ge$_{0.8}$/Sn$_{0.2}$(001) and Ge$_{0.8}$/Sn$_{0.2}$/Ge(001) are much smaller than those for electrons in relaxed Ge mainly due to the increase of interaction caused by the strain between the conduction band and valence bands at the $\Gamma$ point. The lift of degeneracy in Ge/Ge$_{0.8}$/Sn$_{0.2}$(001) and Ge/Ge$_{0.8}$/Sn$_{0.2}$(001) makes m*$_{d}$ and m*$_{c}$ for holes smaller than those in relaxed Ge and results in the decrease of the interband scattering as well as interband scattering. The decrease of the interband scattering is more obvious in Ge/Ge$_{0.8}$/Sn$_{0.2}$(001) because of its large splitting energy between the heavy hole and light hole band. Therefore, Ge/Ge$_{0.8}$/Sn$_{0.2}$(001) is expected to be good candidate for the development of ultra high-speed CMOS device.CMOS device.eed CMOS device.CMOS device.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.378.2-378.2
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• 2014

We have investigated optical characteristics of $p-Ge_{0.99}Sn_{0.01}$ and Ge films grown on Si substrates using photoreflectance (PR) spectroscopy. The $Ge_{0.99}Sn_{0.01}$ and Ge films were grown by using an ultra-high vacuum chemical vapor deposition and molecular beam epitaxy methods, respectively. PR spectra were measured at 25 K and an extended InGaAs detector was used. By comparing $Ge_{0.99}Sn_{0.01}/Si$ and Ge/Si spectra, we observed the signals related to direct transition and split-off band of $Ge_{0.99}Sn_{0.01}$. The transition energies of $Ge_{0.99}Sn_{0.01}$ and Ge films were approximately 0.74 and 0.84 eV, respectively. Considering the shift of split-off band transition of $Ge_{0.99}Sn_{0.01}$, we suppose that the transition at 0.74 eV is attributed to direct transition between ${\Gamma}$ band and valence band. The temperature- and excitation power-dependent PR spectra were also measured.

• Journal of Powder Materials
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• v.9 no.6
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• pp.422-432
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• 2002

Mechanically driven decomposition of intermetallics during mechanical milling(MM 1 was investigated. This process for Fe-Ce and Fe-Sn system was studied using conventional XRD, DSC, magnetization and alternative current susceptibility measurements. Mechanical alloying and milling form products of the following composition (in sequence of increasing Gecontent): $\alpha$(${\alpha}_1$) bcc solid solution, $\alpha$+$\beta$-phase ($Fe_{2-x}Ge$), $\beta$-phase, $\beta$+FeGe(B20), FeGE(B20), FeGe(B20)+$FeGe_2$,$FeGe_2$,$FeGe_2$+Ge, Ge. Incongruently melting intermetallics $Fe_6Ge_5$ and $Fe_2Ge_3$ decompose under milling. $Fe_6Ge_5$ produces mixture of $\hat{a}$-phase and FeGe(B20), $Fe_2Ge_3$ produces mixture of FeGe(B20) and $FeGe_2$ phases. These facts are in good agreement with the model that implies local melting as a mechanism of new phase for-mation during medchanical alloying. Stability of FeGe(B20) phase, which is also incongruently melting compound, is explained as a result of highest density of this phase in Fe-Ge system. Under mechanical milling (MM) in planetary ball mill, FeSn intermetallic decomposes with formation $Fe_5Sn_3$ and $FeSn_2$ phases, which have the biggest density among the phases of Fe-Sn system. If decomposition degree of FeSn is relatively small(<60%), milled powder shows superparamagnetic behavior at room temperature. For this case, magnetization curves can be fitted by superposition of two Langevin functions. particle sizes for ferromagnetic $Fe_5Sn_3$ phase determined from fitting parameters are in good agreement with crystalline sizes determined from XRD data and remiain approximately chageless during MM. The decomposition of FeSn is attributed to the effects of local temperature and local pressure produced by ball collisions.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.496-499
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• 2000

In order to investigate the effect of Ge addition to the Cu Matrix on the microstructure and the critical current density, four kinds of internal tin processed Nb$_3$Sn strands with pure Cu and Cu 0.2, 0.4, 0.6 wt％ Ge alloy were drawn to 0.8 mm diameter. The microstructure and critical current of internal tin processed Nb$_3$Sn wires that were heat treated at temperatures ranging from 68$0^{\circ}C$ to 74$0^{\circ}C$ for 240 h were investigated. The Ge addition to the matrix did not make workability worse. A Ge rich layer in the Cu-Ge matrix suppressed the growth of the Nb$_3$Sn layer and promoted grain coarsening. The greater the Ge content in the matrix, the lower the net Jc result after Nb$_3$Sn reaction heat treatment. There was no significant variation in Jc observed with heat treatment temperature ranging from 68$0^{\circ}C$ to 74$0^{\circ}C$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.104-107
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• 2001

In order to investigate the effect of Ge addition to the Cu matrix on the microstructure and the critical current density, four kinds of internal tin processed Nb$_3$Sn strands with pure Cu and Cu 0.2, 0.4, 0.6 wt % Ge alloys were drawn to 0.8 mm diameter. The microstructure and critical current of internal tin processed Nb$_3$Sn wires that were heat treated at temperatures ranging from 68$0^{\circ}C$ to 74$0^{\circ}C$ for 240h were investigated. The Ge addition to the matrix did not make workability worse. A Ge rich layer in the Cu-Ge matrix suppressed the growth of the Nb$_3$Sn layer and promoted grain coarsening. The greater the Ge content in the matrix, the lower the net Jc result after Nb$_3$sn reaction heat treatment. There was no significant variation in Jc observed with heat treatment temperature ranging from 68$0^{\circ}C$ to 74$0^{\circ}C$. The values of AC loss of Ge added wires were decreased to 40 % compare with no addition wire. Low AC loss was due to segregation of Ge rich layer in the Cu-Ge matrix. If Ge added wire with thin Nb filaments were fabricated, slow diffusion rate of Sn would be overcome and decreased AC loss that is weak Point of internal tin method.

• Journal of the Korean Vacuum Society
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• v.7 no.2
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• pp.77-81
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• 1998

The eptiaxial growth of Ge on the clean and surfactant (Sn) adsorbed surface of Ge(111) was studied by the intensity oscillation of a RHEED specular spot. In the case of epitaxial growth without the adsorbed surfactant, the RHEED intensity oscillation was stable and periodic up to 24 ML at the substrate temperature of $200^{\circ}C$. Therefore the optimum temperature for the epitaxial growth of Ge on clean Ge(111) seems to be $200^{\circ}C$. However, in the case of epitaxial growth with the adsorbed surfactant, the irregular oscillations are observed in the early stage of the growth. The RHEED intensity osicillation was very stable and periodic up to 38 ML, and the d2$\times$2 structure was not charged with continued adsorption of Ge at the substrate temperature of 2002$\times$2. These results may be explained by the fact that the diffusion length of Ge atoms is increased by decreasing the activation energy of the Ge surface diffusion, resulted by segregation of Sn toward the growing surface.

• Journal of the Korean Society of Industry Convergence
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• v.4 no.4
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• pp.451-455
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• 2001

The epitaxial growth of Ge on the clean and surfactant(Sn) adsorbed surface of Ge(111) was studied by the intensity oscillation of a RHEED specular spot. In the case of epitaxial growth without the adsorbed surfactant, the RHEED intensity oscillation was stable and periodic up to 24ML at the substrate temperature of $200^{\circ}C$. Therefore the optimum temperature for the epitaxial growth of Ge on clean Ge(111) seems to be $200^{\circ}C$. However, in the case of epitaxial growth with the adsorbed surfactant, the irregular oscillations are observed in the early stage of the growth. The RHEED intensity oscillation was very stable and periodic up to 38ML, and the $d2{\times}2$ structure was not charged with continued adsorption of Ge at the substrate temperature of $200^{\circ}C$. These results may be explained by the fact that the diffusion length of Ge atoms is increased by decreasing the activation energy of the Ge surface diffusion, resulted by segregation of Sn toward the growing surface. From the desorption process, the desorption energy of Sn in Ge $\sqrt{5}{\times}\sqrt{5}$ structure is observed to be 3.28eV.

• Journal of the Korean Magnetics Society
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• v.23 no.4
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• pp.117-121
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• 2013

In this study we investigated magnetism and magnetostriction of B2-structured FeX (X = Al, Si, Ni, Ga, Ge, and Sn) using a first-principles method, in order to survey the possibility of developing a transition metal based magnetostriction material. The Full-potential Linearized Augmented Plane Wave method was employed for solving the Kohn-Sham equation within the generalized gradient approximation for exchange-correlation interaction between electrons. FeX alloys are stabilized in ferromagnetic states except for the FeSi and FeGe alloys. Magnetostrcition coefficients of FeX (X = Al, Ni, Ga, and Sn) were calculated to be -5, +6, -84, -522ppm, respectively. It is noteworthy that the magnetostriction coefficient (-522ppm) of FeSn is larger than that (+400ppm) of Gafenol.

• Journal of the Korean Magnetics Society
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• v.2 no.2
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• pp.99-104
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• 1992

The permeability vs. temperature curve, the loss factor and the microstructure of a commercial Mn-Zn ferrites were investigated by X-ray diffractometer, SEM and LCR meter, where the additives, such as $SnO_{2}$ and $GeO_{2}$, were added to the main composition. Their wt% were 0.05, 0.3 and 1.0, respectively. When the content of additives increased, the SPM (Secondary Peak Maximum) of the permeability moved from $80^{\circ}C$ to below the room temperature. This movement, without the significant change of the microstructure, is because Sn and Ge, having the different ionic radius, were soluble in the matrix. There was no variation of the permeability with the frequency up to 100 kHz. And the loss factor showed the maximum value at 10 kHz.