• 한국전기전자재료학회논문지
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• 제16권5호
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• pp.390-396
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• 2003

As the design rule of device continued to shrink, the contact resistance in small contact size became important. Although the conventional TiN/Ti structure as a ohmic layer has been widely used, we propose a new TiN/Co film structure. We characterized a contact resistance by using a chain pattern and a KELVIN pattern, and a leakage current determined by current-voltage measurements. Moreover, the microstructure of TiN/ Ti/ silicide/n$\^$+/ contact was investigated by a cross-sectional transmission electron microscope (TEM). The contact resistance by the Co ohmic layer showed the decrease of 26 % compared to that of a Ti ohmic layer in the chain resistance, and 50 ％ in KELYIN resistance, respectively. A Co ohmic layer shows enough ohmic behaviors comparable to the Ti ohmic layer, while higher leakage currents in wide area pattern than Ti ohmic layer. We confirmed that an uniform silicide thickness and a good interface roughness were able to be achieved in a CoSi$_2$ Process formed on a n$\^$+/ silicon junction from TEM images.

• 한국세라믹학회지
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• 제35권10호
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• pp.1070-1077
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• 1998

Effect of current collecting layer on the cathode was characterized by AC impedance spectroscopy at 800$^{\circ}C$ under flowing air. LSM-YSZ composite cathode showed lower polarization resistance due to the in-crease of triple phase (LSM/YSZ/Pore) boundary length by incorporation of YSZ. Ohmic resistance {{{{ {R }_{1 } }} of LSM-YSZ was higher than that of pure LSM however because in-plane resistance of the cathode was fair-ly high due to its high specific resistivity. To reduce the in-plane resistance of LSM-YSZ cathode cathode side current collecting layer was required. Ohmic resistance {{{{ {R }_{1 } }} was reduced after forming LSM current col-lecting layer on the LSM-YSZ cathode. In case of pure LSM cathode the formation of Pt, or LSCO current collecting layer reduced polarization resistance {{{{ {R }_{p } }} but ohmic resistance {{{{ {R }_{1 } }} was relatively constant. After annealing of LSM cathode with Pt current collector at higher temperature polarization resistance {{{{ {R }_{p } }} was in-creased but ohmic resistance {{{{ {R }_{1 } }} was constant. These phenomena indicate that Pt or LSCo current col-lecting layers act as a catalytic layer for oxygen reduction of pure LSM cathode. LSCO current collector was effective in reducing the ohmic and polarization resistance of LSM-YSZ cathode.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.283-283
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• 2011

The n-doping effect by doping metal carbonate into an electron-injecting organic layer can improve the device performance by the balanced carrier injection because an electron ohmic contact between cathode and an electron-transporting layer, for example, a high current density, a high efficiency, a high luminance, and a low power consumption. In the study, first, we investigated an electron-ohmic property of electron-only device, which has a ITO/$Rb_2CO_3$-doped $C_{60}$/Al structure. Second, we examined the I-V-L characteristics of all-ohmic OLEDs, which are glass/ITO/$MoO_x$-doped NPB (25%, 5 nm)/NPB (63 nm)/$Alq_3$ (32 nm)/$Rb_2CO_3$-doped $C_{60}$(y%, 10 nm)/Al. The $MoO_x$doped NPB and $Rb_2CO_3$-doped fullerene layer were used as the hole-ohmic contact and electron-ohmic contact layer in all-ohmic OLEDs, respectively, Third, the electronic structure of the $Rb_2CO_3$-doped $C_{60}$-doped interfaces were investigated by analyzing photoemission properties, such as x-ray photoemission spectroscopy (XPS), Ultraviolet Photoemission spectroscopy (UPS), and Near-edge x-ray absorption fine structure (NEXAFS) spectroscopy, as a doping concentration at the interfaces of $Rb_2CO_3$-doped fullerene are changed. Finally, the correlation between the device performance in all ohmic devices and the interfacial property of the $Rb_2CO_3$-doped $C_{60}$ thin film was discussed with an energy band diagram.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 하계학술대회 논문집 Vol.5 No.1
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• pp.417-420
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• 2004

The electrical effects of dry-etch on n-type GaN by an inductively coupled $Cl_2/CH_4/H_2/Ar$ plasma were investigated as a function of ion energy, by means of ohmic and Schottky metallization method. The specific contact resistivity(${\rho}_c$) of ohmic contact was decreased, while the leakage current in Schottky diode was increased with increasing ion energy due to the preferential sputtering of nitrogen. At a higher rf power, an additional effect of damage was found on the etched sample, which was sensitive to the dopant concentration in terms of the ${\rho}_c$ of ohmic contact. This was attributed to the effects such as the formation of deep acceptor as well as the electron-enriched surface layer within the depletion layer. Furthermore, thermal annealing process enhanced the ohmic and Schottky property of heavily damaged surface.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.1
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• pp.290-293
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• 2003

Ohmic contact characteristics of Al ion implanted n-type SiC wafer were investigated. Al ions implanted with high dose to obtain the final concentration of $5{\times}10^{19}/cm^3$, then annealed at high temperature. Firstly, B ion ion implanted p-well region were formed which is needed for fabrication of SiC devices such as DIMOSFET and un diode. Secondly, Al implanted high dose region for ohmic contact were formed. After ion implantation, the samples were annealed at high temperature up to $1600^{\circ}C\;and\;1700^{\circ}C$ for 30 min in order to activate the implanted ions electrically. Both the inear TLM and circular TLM method were used for characterization. Ni/Ti metal layer was used for contact metal which is widely used in fabrication of ohmic contacts for n-type SiC. The metal layer was deposited by using RF sputtering and rapid thermal annealed at $950^{\circ}C$ for 90sec. Good ohmic contact characteristics could be obtained regardless of measuring methods. The measured specific contact resistivity for the samples annealed at $1600^{\circ}C\;and\;1700^{\circ}C$ were $1.8{\times}10^{-3}{\Omega}cm^2$, $5.6{\times}10^{-5}{\Omega}cm^2$, respectively. Using the same metal and same process of the ohmic contacts in n-type SiC, it is found possible to make a good ohmic contacts to p-type SiC. It is very helpful for fabricating a integrated SiC devices. In addition, we obtained that the ratio of the electrically activated ions to the implanted Al ions were 10% and 60% for the samples annealed at $1600^{\circ}C\;and\;1700^{\circ}C$, respectively.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.157-157
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• 2010

Vertical-structure light-emitting diodes (V-LEDs) by laser lift-off (LLO) have been exploited for high-efficiency GaN-based LEDs of solid-state lightings. In V-LEDs, emitted light from active regions is reflected-up from reflective ohmic contacts on p-GaN. Therefore, silver (Ag) is very suitable for reflective contacts due to its high reflectance (>95%) and surface plasmon coupling to visible light emissions. In addition, low contact resistivity has been obtained from Ag-based ohmic contacts annealed in oxygen ambient. However, annealing in oxygen ambient causes Ag to be oxidized and/or agglomerated, leading to degradation in both electrical and optical properties. Therefore, preventing Ag from oxidation and/or agglomeration is a key aspect for high-performance V-LEDs. In this work, we demonstrate the enhanced thermal stability of Ag-based Ohmic contact to p-GaN by reducing the thermal compressive stress. The thermal compressive stress due to the large difference in CTE between GaN ($5.6{\times}10^{-6}/^{\circ}C$) and Ag ($18.9{\times}10^{-6}/^{\circ}C$) accelerate the diffusion of Ag atoms, leading to Ag agglomeration. Therefore, by increasing the additional residual tensile stress in Ag film, the thermal compressive stress could be reduced, resulting in the enhancement of Ag agglomeration resistance. We employ the thin Ni layer in Ag film to form Ni/Ag mutli-layer structure, because the lattice constant of NiO ($4.176\;{\AA}$ is larger than that of Ag ($4.086\;{\AA}$). High-resolution symmetric and asymmetric X-ray diffraction was used to measure the in-plane strain of Ag films. Due to the expansion of lattice constant by oxidation of Ni into NiO layer, Ag layer in Ni/Ag multi-layer structure was tensilely strained after annealing. Based on experimental results, it could be concluded that the reduction of thermal compressive stress by additional tensile stress in Ag film plays a critical role to enhance the thermal stability of Ag-based Ohmic contact to p-GaN.

• 한국광학회:학술대회논문집
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• 한국광학회 2008년도 동계학술발표회 논문집
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• pp.93-94
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• 2008

In order to suppress the current crowding in light emitting diodes (LEDs) grown on sapphire substrate, the effect of nonuniform contact resistivity between TME layer and p-GaN layer on the LED surface was theoretically investigated. The analysis results showed that current crowding occurring around p-electrode could be considerably improved, which in turn would be helpful to improve the electrostatic discharge (ESD) characteristic.

• 대한전자공학회논문지
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• 제26권10호
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• pp.1545-1553
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• 1989

The ohmic contact behavior in HEMT structure was compared with that in MESFET one throughout the specific contact resistance and microstructural change in both structures. A Au-Ge-Ni based metallization scheme was used and the alloying temperature of the ohmic materials was changed from 330\ulcorner to 550\ulcorner. The alloying temperature to obtain the minimum specific contact resistance in HEMT structure was 60k higher than that in MESFET. The volume fraction of NiAs (Ge) in MESFET structure increases with alloying temperature and/or the alloying time, which makes the decrease of specific contact resistance at the initial stage of ohmic metallization. In contrast, the volume fraction of NiAs(Ge) in HEMT structure was not dependent upon the specific contact resistance, which implies that the ohmic contacts are dominantly formed by the Ge diffusion to 2-DEG(two dimensional electron gas) layer.

• 한국전기전자재료학회논문지
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• 제17권7호
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• pp.764-769
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• 2004

In order to reduce operating voltage of the GaN based blue-violet laser diodes, the effect of highly Mg doped GaN layer, which was grown below ohmic contact metals, on contact resistivity as well as operating voltage has been investigated. The addition of the highly Mg doped GaN layer greatly reduced contact resistivity of Pd/Pt/Au ohmic contacts from $5.2 \times {10}^-2 \Omegaㆍ$\textrm{cm}^2$ to 7.5 \times {10}^-4 \Omegaㆍ$\textrm{cm}^2$$. In addition, it also decreased device voltage at 20 mA by more than 3 V. Temperature- dependent sheet resistivity of the highly Mg doped GaN layer suggested that the reduction of the contact resistivity could be attributed to predominant current flow at the interface between the Pd/Pt/Au contacts and p-GaN through a deep level defect band, rather than the valence band.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.209.2-209.2
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• 2015

Two dimensional layered materials, such as transition metal dichalcogenides (TMDs) family have been attracted significant attention due to novel physical and chemical properties. Among them, molybdenum disulfide ($MoS_2$) has novel physical phenomena such as absence of dangling bonds, lack of inversion symmetry, valley degrees of freedom. Previous studies have shown that the interface of metal/$MoS_2$ contacts significantly affects device performance due to presence of a scalable Schottky barrier height at their interface, resulting voltage drops and restricting carrier injection. In this study, we report a new device structure by using few-layer graphene as the bottom interconnections, in order to offer Schottky barrier free contact to bi-layer $MoS_2$. The fabrication of process start with mechanically exfoliates bulk graphite that served as the source/drain electrodes. The semiconducting $MoS_2$ flake was deposited onto a $SiO_2$ (280 nm-thick)/Si substrate in which graphene electrodes were pre-deposited. To evaluate the barrier height of contact, we employed thermionic-emission theory to describe our experimental findings. We demonstrate that, the Schottky barrier height dramatically decreases from 300 to 0 meV as function of gate voltages, and further becomes negative values. Our findings suggested that, few-layer graphene could be able to realize ohmic contact and to provide new opportunities in ohmic formations.