• Proceedings of the Materials Research Society of Korea Conference
• /
• 2011.05a
• /
• pp.243.2-243.2
• /
• 2011

ZnO materials with a wide band gap of approximately 3.3 eV has been used in transparent conducting oxides (TCO) due to exhibitinga high optical transmission, but its low conductivity acts as role of a limitation for conducting applications. Recently, Ga or Al-doped ZnO (GZO, AZO) becomes transparent conducting materials because of high optical transmission and excellent conductivity. However, the fundamental mechanism underlying the improvement of electrical conductivity of the GZO is still the subject of debate. In this study, we have fully investigated the reasons of high conductivity through the characterization of plane defects, crystal orientation, doping contents, crystal structure in Zn1-xGaxO (x=0, 3, 5.1, 5.6, 6.6 wt%). We manufactured Zn1-xGaxO by sintering ZnO and Ga2O3 powers, having a theoretical density of 99.9% and homogeneous Ga-dopant distribution in ZnO grains. The GZO containing 5.6 wt% Ga represents the highest electrical conductivity of $7.5{\times}10^{-4}{\Omega}{\cdot}m$. In particular, many twins and superlattices were induced by doping Ga in ZnO, revealed by X-ray diffraction measurements and TEM (transmission electron microscopy) observations. Twins developed in conventional ZnO crystal are generally formed at (110) and (112) planes, but we have observed the twins at (113) plane only, which is the first report in ZnO material. Interestingly, the superlattice structure was not observed at the grains in which twins are developed and the opposite case was true. This structural change in the GZO resulted in the difference of electrical conductivity. Enhancement of the conductivity was closely related to the extent of Ga ordering in the GZO lattice. Maximum conductivity was obtained at the GZO with a superlattice structure formed ideal ordering of Ga atoms.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.25 no.11
• /
• pp.1294-1303
• /
• 1988

Electron and hole traps in semi-insulating GaAs with activation energies ({\Delta}E_r) ranging from 0.16 $\pm$ 0.01 to 0.98 $\pm$ 0.01 eV, have been detected and characterized by photo-induced current transient measurements. SI undoped GaAs has fewer deep levels than SI GaAs: Cr. The thermal capture cross section and density of the traps have been estimated and some of the centers have been related to native defects. In particular, the activation energy of the compensating Cr, and "0" levels in semi-insulating GaAs were accurately measured. The transient measurements were complemented by Hall measurements at T > 300K and photocurrent spectra measurements. The transition energies for the deep compensating levels obtained by the analyses of data from these measurements, when compared with those from the transient measurements, indicate negligible lattice-coupling of these centers. Analysis of the transport data also indicates that neutral impurity scattering plays a significant role in semi-insulating materials at high temperatures.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.31 no.1
• /
• pp.32-39
• /
• 2011

The object of this study is to evaluate and discriminate nondestructively the dislocation substructures of Cu and Cu-Zn alloy subjected to the low-cycle-fatigue. The ultrasonic wave velocity, electrical resistivity and positron annhilation lifetime(PAL) were measured to the nondestructive testing. Cyclic fatigue test of Cu and Cu-Zn alloy with much different stacking fault energies was conducted and the correlations between dislocation behavior and nondestructive parameters were studied. Dislocation cell substructure was developed in Cu, while planar array of dislocation structure was developed in Cu-35Zn alloy only increasing dislocation density with fatigue cycles. Decrease in ultrasonic wave velocity, increase in electrical resistivity and PAL were shown because of the development of lattice defects, dislocations and vacancies, by cyclic fatigue at room temperature. In contrast to Cu-Zn alloy of the planar-array dislocation substructure showing continuous changes in the nondestructive parameters, it does not make any noticeable changes in the nondestructive parameters after the evolution of dislocation cell substructure in Cu.

• Analytical Science and Technology
• /
• v.13 no.2
• /
• pp.200-207
• /
• 2000

The growth mechanisms of graphite spherulite both in the nodular cast iron and the high pressuretreated Ni-C alloy were investigated by SEM, HRTEM and EELS. The internal microstructure and lattice image of graphite spherulite extracted from Ni-C alloy were compared with those of graphite spherulite extracted from the nodular cast iron. The ratios of $sp^2$ and $sp^3$ bonding in the respective graphite spherulite measured by EELS, are compared each other. The graphite spherulite of Ni-C alloy had little internal defects and much $sp^3$ carbon species compared to that of the nodular cast iron. Present difference in microstructural features and bonding characters indicated that the graphite spheruites in the high pressuretreated Ni-C alloy grew by different mechanism compared with those in the nodular cast iron.

• Analytical Science and Technology
• /
• v.6 no.2
• /
• pp.197-205
• /
• 1993

Blends of elemental Ni and 20 weight % Cr powder were milled for different period in a laboratory attritor. Powder size distribution, microstructure and X-ray diffraction characteristics were investigated as a function of processing period. Saturated magnetization, Ms and coercive force, Hc we also measured and compared with plasma melted ingot to confirm the mechanically alloyed states. Mechanical alloying occurred as a consequence of the partition of powders and the increase of interfacial area driving diffusing of Cr into Ni. However, magnetic properties of chemically homogeneous solid solution like melted ingot has not been observed even though steady state of submicron grain size has been achieved after milling over 15 hrs. Further mechanical alloying period gave refinement of grain size, which resulted in the increase of alloyed layer. It is concluded that homogenization should be controlled by the increase of interfacial area between constitutive powders caused by plastic particle deformation and by the diffusion of Cr within the alloyed phase into Ni-rich phase through lattice defects.

• Nuclear Engineering and Technology
• /
• v.51 no.8
• /
• pp.1983-1990
• /
• 2019

Spray deposited Molybdenum trioxide (MoO₃) thin film of thickness nearly 379 nm were irradiated with 200 MeV Ag¹⁵⁺ ion beam at different fluences (Ø) of 5 ×10¹¹, 1 × 10¹², 5 × 10¹² and 1 × 10¹³ ions/㎠. The X-ray diffraction (XRD) pattern of the pristine film confirms orthorhombic structure and the crystallinity decreased after irradiation with the fluence of 5 × 10¹¹ ions/㎠ due to irradiation induced defects and became amorphous at higher fluence. In pristine film, Raman modes at 665, 820, 996 cm^-1 belong to Mo-O stretching, 286 cm^-1 belong to Mo-O bending mode and those below 200 cm^-1 are associated with lattice modes. Raman peak intensities decreased upon irradiation and vanished completely for the ion fluence of 5 ×10¹² ions/㎠. The percentage of optical transmittance of pristine film was nearly 40%, while for irradiated films it decreased significantly. Red shift was observed for both the direct and indirect band gaps. The pristine film surface had densely packed rod like structures with relatively less porosity. Surface roughness decreased significantly after irradiation. The electrical transport properties were also studied for both the pristine and irradiated films by Hall effect. The results are discussed.

• Nuclear Engineering and Technology
• /
• v.52 no.11
• /
• pp.2585-2593
• /
• 2020

Swift heavy ion (SHI) beam irradiation can generate desirable defects in materials by transferring sufficient energy to the lattice that favours huge possibilities in tailoring of materials. The effect of Ag¹⁵⁺ ion irradiation with energy 200 MeV on spray deposited V₂O₅ thin films of thickness 253 nm is studied at various ion doses from 5 × 10¹¹ to 1 × 10¹³ ions/㎠. The XRD results of pristine film confirmed orthorhombic structure of V₂O₅ and its average crystallite size was found to be 20 nm. The peak at 394 cm^-1 in Raman spectra confirmed O-V-O bonding of V₂O₅, whereas 917 cm^-1 arise because of distortion in stoichiometry by a loss of oxygen atoms. Raman peaks vanished completely above the ion fluence of 5 × 10¹² ions/㎠. Optical studies by UV-Vis spectroscopy shows decrement in transmittance with an increase in ion fluence up to 5 × 10¹² ions/㎠. The red shift is observed both in the direct and indirect band gaps until 5 × 10¹² ions/㎠. The surface topography of the pristine film revealed sheath like structure with randomly distributed spherical nano-particles. The roughness of film decreased and the density of spherical nanoparticles increased upon irradiation. Irradiation improved the conductivity significantly for fluence 5 × 10¹¹ ions/㎠ due to band gap reduction and grain growth.

• Korean Journal of Crystallography
• /
• v.7 no.1
• /
• pp.73-80
• /
• 1996

The single crystal growth has been carried out with the newly designed 1-T HB(single temperature zone horizontal Bridgman) system for GaAs crystals of 2 inch diameter doped with Si, Zn or undoped. With this method, incidence probability of single crystallinity was shown to be 0.73. Lattice defects evaluated from EPD(etch pit density) measurement were in the range of 5,000-20,000/cm2, dependent upon the doping condition. For the undoped GaAs crystals, carrier concentrations from the Hall measurement were ∼1×1016/cm3 at the seed part, which were less than half the concentrations of double of triple temperature zone(2-T, 3-T) HB grown crystals. By the 1-T HB method, therefore, GaAs crystals can be grown successfully with better yield and higher purity.

• Journal of the Mineralogical Society of Korea
• /
• v.22 no.4
• /
• pp.407-415
• /
• 2009

The change of the nitrogen-related centers and the color change of electron beam irradiated type Ia natural diamonds were studied. The irradiation of diamond with high-energy electron beam creates lattice defects which are neutral single vacancy $V^0$. It increased with increasing electron dose density. The B aggregation seems to produce vacancies more easily than the A aggregation, because diamonds with more B aggregation have more platelets, which are sufficient breakable size by electron beam. Greenish blue color of irradiated diamond is changed to darker with increasing electron dose density. GR1 centers with a zero-phonon line at 741 nm and phonon sidebands make transmit visible light at 530 nm and it moves to 500 nm with higher intensity of GR1 centers.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.52 no.12
• /
• pp.545-552
• /
• 2003

When a Si PIN diode is exposed to fast neutrons, it results in displacement damage to the Si lattice structure of the diode. Defects induced from structural dislocation become effective recombination centers for carriers which pass through the base of a PIN diode. Hence, increasing the resistivity of the diode decreases the current for the applied forward voltage. This paper involves the development of a neutron sensor based on the phenomena of the displacement effect damaged by neutron exposure. The neutron effect on the semiconductor was analyzed. Several PIN diode arrays with various thickness and cross-section area of the intrinsic layer(I layer) were fabricated. Under irradiation tests with a neutron beam, the manufactured diodes have a good linearity to neutron dose and show that the increase of thickness of I layer and the decrease of cross-section of PIN diodes improve the sensitivity. Newly developed PIN diodes with thicker I layer and various cross section, were retested and then showed the best neutron sensitivity at the condition that the I layer thickness was similar to a side length. On the basis of two test results, final discrete PIN diodes with a rectangular shape were manufactured and the characteristics as neutron detectors were analyzed through the neutron beam test using on-line electronic dosimetry system. Developed PIN diode shows a good linearity as dosimetry in the range of 0 to 1,000cGy(Tissue) and its neutron sensitivity is 13mV/cGy at constant current of 5mA, that is three times higher than that of commercially available neutron detectors. And the device shows little dependency on the orientation of the neutron beam and a considerable stability in annealing test for a long period.