• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1378-1380
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• 2001

Ohmic contacts have been fabricated on p-type 4H-SiC using Pt/Ti. Low resistivitf Ohmic contacts of Pt/Ti to p-type 4H-SiC were investigated. Specific contact resistances were measured using the transmission line model method, and the physical properties of the contacts were examined using x-ray diffraction, scanning electron microscopy. Ohmic behavior with linear current-voltage characteristics was observed following anneals at $900^{\circ}C$ for 90sec at a pressure of $3.4{\times}10^{-5}$ Torr. The Pt/Si/Ti films was measured lower value of the specific contact resistance by the annealing process, and the contact resistances were improved more than one order compared to Ti contact the annealed sample. Scanning electron microscopy shows that the Pt layer effectively reduce the oxidation of Ti films. And results are obtained as $4.6{\times}10^{-4}$ ohm/$cm^2$ for a Pt/Ti metal structure after a vacuum annealing at $900^{\circ}C$ for 90sec. Titanium has a relatively high melting point, thus Ti-based metal contacts were attempted in this study.

• Proceedings of the KIEE Conference
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• 2001.11a
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• pp.112-114
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• 2001

In this letter, we report on the investigation of Si/Ti, Pt/Si/Ti, Co/Si/Ti Ohmic contacts to p-type 4H-SiC. The contacts were formed by a 2-step vacuum annealing at $550^{\circ}C$ for 5 min, $850^{\circ}C$ for 2 min respectively. The contact resistances were measured using the transmission line model method, which resulted in specific $10^{-4}{\Omega}cm^2$, and the physical properties of the contactcontact resistivities in the $9.2{\times}10^{-4}$, $7.1{\times}10^{-4}$ and $4.5{\times}s$ were examined using microscopy, AES(auger electron spectroscopy). AES analysis has shown that, at this anneal temperature, there was a intermixing of the Ti and Si, migration of into SiC. Overlayer of Pt, Co had the effect of decreasing the specific contact resistivity and improving the surface morphology of the annealed contact.

• Korean Journal of Materials Research
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• v.31 no.8
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• pp.445-449
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• 2021

Zintl compound Mg₃Sb₂ is a promising candidate for efficient thermoelectric material due to its small band gap energy and characteristic electron-crystal phonon-glass behavior. Furthermore, this compound enables fine tuning of carrier concentration via chemical doping for optimizing thermoelectric performance. In this study, nominal compositions of Mg_3.8Sb_2-xTe_x (0 ≤ x ≤ 0.03) are synthesized through controlled melting and subsequent vacuum hot pressing method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) are carried out to investigate phase development and surface morphology during the process. It should be noted that 16 at. % of excessive Mg must be added to the system to compensate for the loss of Mg during melting process. Herein, thermoelectric properties such as Seebeck coefficient, electrical conductivity, and thermal conductivity are evaluated from low to high temperature regimes. The results show that Te substitution at Sb sites effectively tunes the majority carriers from holes to electrons, resulting in a transition from p to n-type. At 873 K, a peak ZT value of 0.27 is found for the specimen Mg_3.8Sb_1.99Te_0.01, indicating an improved ZT value over the intrinsic value.

• Journal of the Korean Ceramic Society
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• v.54 no.6
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• pp.518-524
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• 2017

A flexible thermoelectric device using body heat has drawn attention as a power source for wearable devices. In this study, thermoelectric thick films were fabricated by cold pressing method using p-type antimony telluride and n-type bismuth telluride powders in accordance with specific loads. Thermoelectric thick films were denser and improved the electrical and thermoelectric properties while increasing the load of the cold pressing. The thickness of the specimen can be controlled by the amount of material; specimens were approximately 700 um in thickness. Flexible thermoelectric devices were manufactured by using the thermoelectric thick films on PI (Polyimide) substrate. The process is cheap, efficient, easy and scalable. Evaluation of power generation performance and flexibility on the fabricated flexible thermoelectric device was carried out. The flexible thermoelectric device has great flexibility and good performance and can be applied to wearable electronics as a power source.

• Current Photovoltaic Research
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• v.9 no.3
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• pp.75-83
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• 2021

The tunnel oxide passivated contact (TOPCon) structure got more consideration for development of high performance solar cells by the introduction of a tunnel oxide layer between the substrate and poly-Si is best for attaining interface passivation. The quality of passivation of the tunnel oxide layer clearly depends on the bond of SiO in the tunnel oxide layer, which is affected by the subsequent annealing and the tunnel oxide layer was formed in the suboxide region (SiO, Si₂O, Si₂O₃) at the interface with the substrate. In the suboxide region, an oxygen-rich bond is formed as a result of subsequent annealing that also improves the quality of passivation. To control the surface morphology, annealing profile, and acceleration rate, an oxide tunnel junction structure with a passivation characteristic of 700 mV or more (V_oc) on a p-type wafer could achieved. The quality of passivation of samples subjected to RTP annealing at temperatures above 900℃ declined rapidly. To improve the quality of passivation of the tunnel oxide layer, the physical properties and thermal stability of the thin layer must be considered. TOPCon silicon solar cell has a boron diffused front emitter, a tunnel-SiO_x/n⁺-poly-Si/SiN_x:H structure at the rear side, and screen-printed electrodes on both sides. The saturation currents J_o of this structure on polished surface is 1.3 fA/cm² and for textured silicon surfaces is 3.7 fA/cm² before printing the silver contacts. After printing the Ag contacts, the J_o of this structure increases to 50.7 fA/cm² on textured silicon surfaces, which is still manageably less for metal contacts. This structure was applied to TOPCon solar cells, resulting in a median efficiency of 23.91%, and a highest efficiency of 24.58%, independently. The conversion efficiency of interdigitated back-contact solar cells has reached up to 26% by enhancing the optoelectrical properties for both-sides-contacted of the cells.

• Journal of the Korean Magnetics Society
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• v.15 no.2
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• pp.109-112
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• 2005

Electronic and magnetic properties of $Ti_{1-x}M_xO_{2-\delta}$ (M=Co and Fe) thin films grown by sol-gel method have been investigated. Anatase and rutile $Ti_{1-x}Co_xO_{2-\delta}$ films were successfully grown on $Al_2O_3$ (0001) substrates and exhibited p-type electrical conductivity while the undoped films n-type conductivity. Room temperature vibrating sample magnetometry measurements on the anatase and rutile $Ti_{1-x}Co_xO_{2-\delta}$ films with same x ($=4.8 at.{\%}$) showed quite similar magnetic hysteresis curves with the saturation magnetic moment of $\~4 {\mu}_B$ per Co ion despite their differences in structural and electronic properties. Such giant magnetic moment is attributable to the unquenched orbital moment of the $Co^{2+}$ ions substituting the octahedral $Ti^{4+}$ sites. Similar ferromagnetic behavior was observed for $Ti_{1-x}Fe_xO_{2-\delta}$ films that are highly resistive compared to the Co doped samples. Saturation magnetic moment was found to decrease for higher x, i.e., $\~2$ and $\~1.5 {\mu}_B$ per Fe ion for x=2.4 and 5.8 at. $\%$, respectively. Conversion electron $M\ddot{o}ssbauer$ spectroscopy measurements predicted the coexistence of $Fe^{2+}$ and $Fe^{3+}$ ions at the octahedral sites of $Ti_{1-x}Fe_xO_{2-\delta}$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.179-182
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• 2004

The $p-CdIn_2Te_4$ single crystal was grown in the three-stage vertical electric furnace by using Bridgman method. The quality of the grown crystal has been investigated by the x-ray diffraction and the photoluminescence measurements. From the Photoluminescence spectra of the as-grown $CdIn_2Te_4$ crystal and the various heat-treated crystals, the $(D^{o},X)$ emission was found to be the dominant intensity in the photoluminescence spectrum of the $CdIn_2Te_4:Cd$, while the $(A^{o},X)$ emission completely disappeared in the $CdIn_2Te_4:Cd$. However, the $(A^{o},X)$ emission in the photoluminescence spectrum of the $CdIn_2Te_4:Te$ was the dominant intensity like an as-grown $p-CdIn_2Te_4$ crystal. These results indicated that the $(D^{o},X)$ is associated with $V_{Te}$ acted as donor and that the $(A^{o},X)$ emission is related to $V_{Cd}$ acted as acceptor, respectively. The $p-CdIn_2Te_4$ crystal was found to be obviously converted into the n-type after annealing in the Cd atmosphere. The origin of $(D^{o},\;A^{o})$ emission and its TO Phonon replicas is related to the interaction between donors such as $V_{Te}$ or $Cd_{int}$, and accepters such as $V_{Cd}$ or $Te_{int}$. Also, the In in the $CdIn_2Te_4$ was confirmed not to form the native defects because it existed in the stable form of bonds.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.1033-1036
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• 2004

Si nanocrystallites thin films on p-type (100) Si substrate have been fabricated by pulsed laser deposition using a Nd:YAG laser. After deposition, samples were annealed at the temperatures of 400 to $800^{\circ}C$. Hydrogen passivation was then performed in the forming gas (95% $N_2$ + 5% $H_2$) for 1 hr. Strong violet-indigo photoluminescence has been observed at room temperature from nitrogen ambient-annealed Si nanocrystallites. The variation of photoluminescence (PL) Properties of Si nanocrystallites thin films has been investigated depending on annealing temperatures with hydrogen passivation. From the results of PL, Fourier transform infrared (FTIR), and high-resolution transmission electron microscopy (HRTEM) measurements, it is observed that the origin of violet-indigo PL from the nanocrystalline silicon in the silicon oxide film is related to the quantum size effect of Si nanocrystallites and oxygen vacancies in the SiOx(x : 1.6-1.8) matrix affects the emission intensity.

• Proceedings of the KIEE Conference
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• 1988.11a
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• pp.372-375
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• 1988

The III-V ternary alloy semiconductor $In_{l-x}Ga_{x}As$ were grown by the temperature Gradient of $0.60{\leq}x{\leq}0.98$. The electrical properties were investigated by the Hall effect measurement with the Van der Pauw method in the temperature range of $90{\sim}300K$. $In_{l-x}Ga_{x}As$ were revealed n-type and the carrier concentration at 300K were in the range of $9.69{\times}10^{16}cm^{-3}{\sim}7.49{\times}10^{17}cm^{-3}$. The resistivity was increased and the carrier mobility was decreased with increasing the composition ratio. The optical energy gap determined by optical transmission were $20{\sim}30meV$ lower than theoretical valves on the basis of absorption in the conduction band tail and it was decreased with increasing the temperature by the Varshni rule. In the photoluminescence of undoped $In_{l-x}Ga_{x}As$ at 20K, the main emission was revealed by the radiative recombination of shallow donor(Si) to acceptor(Zn) and the peak energy was increased with increasing the composition, X. The diffusion depth of Zn increases proportionally with the square root of diffusion time, and the activation energy for the Zn diffusion into $In_{0.10}Ga_{0.90}As$ was 2.174eV and temperatures dependence of diffusion coefficient was D = 87.29 exp(-2.174/$K_{B}T$). The Zn diffusion p-n $In_{x}Ga_{x}As$ diode revealed the good rectfying characteristics and the diode factor $\beta{\approx}2$. The electroluminescence spectrum for the Zn-diffusion p-n $In_{0.10}Ga_{0.90}As$ diode was due to radiative recombation between the selectron trap level(${\sim}140meV$) and Zn acceptor level(${\sim}30meV$). The peak energy and FWHM of electroluminescence spectrum at 77K were 1.262eV and 81.0meV, respectively.

• Korean Journal of Materials Research
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• v.8 no.11
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• pp.1055-1060
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• 1998

Thermoelectric properties of ($Pb_{1-x}Sn_x$)Te ($0\leq{x}\leq{0.4}$) alloys, fabricated by mechanical alloying and hot pressing, were investigated with variation of the SnTe content. For the hot-pressed PbTe and ($Pb_{0.9}Sn_{0.1}$)Te. transition from p-type to n-type occurred at $200^{\circ}C$ and $300^{\circ}C$, respectively. However, the specimens containing SnTe more than 0.2mole exhibited p-type conduction up to 450'C. In extrinsic conduction region, the Seebeck coefficient and electrical resistivity of the hot-pressed ($Pb_{1-x}Sn_x$)Te decreased with increasing the SnTe content. The temperature at which the hot-pressed (Pbl-,Sn,)Te exhibited a maximum figure-of-merit was shifted to higher temperature with increasing the SnTe content The hot-pressed (Pbo ,Sno dTe exhibited a maximum figure-of-merit of $0.68\times10_{-3}/K$ at $200^{\circ}C$.