• Journal of the Korean Vacuum Society
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• v.20 no.2
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• pp.77-85
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• 2011

The silicon-germanium (SiGe) alloy, which is compatible with silicon semiconductor technology and has a smaller band gap and a lower thermal conductivity than silicon, has been used to fabricate electronic devices such as transistors, photodetectors, solar cells, and thermoelectric devices. This paper reviews the application of SiGe alloys to electronic devices and related technical issues. Since the SiGe alloy comprises germanium whose band gap is smaller than silicon, its band gap is also smaller than that of silicon irrespective of the ratio of silicon to germanium. This narrow band gap of SiGe enables the base thickness of bipolar transistors to decrease without a loss in current gain so that it is possible to improve the speed of bipolar transistors by adopting the SiGe-base. In addition, the conversion efficiency of solar cells is enhanced by the absorption of long-wavelength light in the SiGe absorption layer. Phonon scattering caused by the irregular distribution of alloying elements induces the lower thermal conductivity of SiGe than those of pure silicon and germanium. Because a thin film layer with a low thermal conductivity suppresses thermal conduction through a thermal sink, the SiGe alloy is considered to be a promising material for silicon-based thermoelectric systems.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.3
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• pp.13-19
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• 2021

This study examined the effects of stacking faults on the thermoelectric properties for n-type SiC semiconductors. Porous SiC semiconductors with 30~42 % porosity were fabricated by the heat treatment of pressed ��-SiC powder compacts at 1600~2100 ℃ for 20~120 min in an N2 atmosphere. XRD was performed to examine the stacking faults, lattice strain, and precise lattice parameters of the specimens. The porosity and surface area were analyzed, and SEM, TEM, and HRTEM were carried out to examine the microstructure. The electrical conductivity and the Seebeck coefficient were measured at 550~900 ℃ in an Ar atmosphere. The electrical conductivity increased with increasing heat treatment temperature and time, which might be due to an increase in carrier concentration and improvement in grain-to-grain connectivity. The Seebeck coefficients were negative due to nitrogen behaving as a donor, and their absolute values also increased with increasing heat treatment temperature and time. This might be due to a decrease in stacking fault density, i.e., a decrease in stacking fault density accompanied by grain growth and crystallite growth must have increased the phonon mean free path, enhancing the phonon-drag effect, leading to a larger Seebeck coefficient.

• ETRI Journal
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• v.41 no.2
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• pp.254-261
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• 2019

Distinct from conventional energy-harvesting (EH) technologies, such as the use of photovoltaic, piezoelectric, and thermoelectric effects, betavoltaic energy conversion can consistently generate uniform electric power, independent of environmental variations, and provide a constant output of high DC voltage, even under conditions of ultra-low-power EH. It can also dramatically reduce the energy loss incurred in the processes of voltage boosting and regulation. This study realized betavoltaic cells comprised of p-i-n junctions based on silicon carbide, fabricated through a customized semiconductor recipe, and a Ni foil plated with a Ni-63 radioisotope. The betavoltaic energy converter (BEC) includes an array of 16 parallel-connected betavoltaic cells. Experimental results demonstrate that the series and parallel connections of two BECs result in an open-circuit voltage $V_{oc}$ of 3.06 V with a short-circuit current $I_{sc}$ of 48.5 nA, and a $V_{oc}$ of 1.50 V with an $I_{sc}$ of 92.6 nA, respectively. The capacitor charging efficiency in terms of the current generated from the two series-connected BECs was measured to be approximately 90.7%.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.10
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• pp.825-829
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• 2015

Theoretical calculations suggest that the thermoelectric figure of merit (ZT) can be improved by introducing a core-shell heterostructure to a semiconductor nanowire because of the reduced thermal conductivity of the nanowire. To experimentally verify the decrease in thermal conductivity in core-shell nanowires, the thermal conductivity of Ge-SixGe1-x core-shell nanowires grown by chemical vapor deposition (CVD) was measured using suspended microdevices. The silicon composition (Xsi) in the shells was measured to be about 0.65, and the remainder of the germanium in the shells was shown to play a role in decreasing defects originating from the lattice mismatch between the cores and shells. In addition to the standard four-point current- voltage (I-V) measurement, the measurement configuration based on the Wheatstone bridge was attempted to enhance the measurement sensitivity. The measured thermal conductivity values are in the range of 9-13 W/mK at room temperature and are lower by approximately 30 than that of a germanium nanowire with a comparable diameter.