Kwang-Chon Kim

Ar+ induced interfacial mixing and phase formation in the Al/Cr system

Abstract Evaporated Al/Cr bilayer thin films were irradiated by 80 keV Ar+ at doses in the range from 1 × 1015 to 2 × 1016 Ar+/cm2 at room temperature in order to investigate the Ar+ induced interfacial mixing behavior and the phase formation and transition by Ar+ bombardment. Ion bombardment induces intermixing across the Al/Cr interface and mixing variance increases with increasing ion dose. Cascade and thermal spike models are found to be not adequate for the ion beam mixing mechanism at room temperature in this system. The Al13Cr2 phase is formed as an initial phase by ion beam mixing and then transforms into the Al11Cr2 or Al4Cr phases at subsequent ion bombardment. This result is discussed in terms of the enhanced atomic mobility and the thermodynamical driving force by introducing the concept of an effective heat of formation.

Thermoelectric Properties of Bi 2 Te 3 Films Grown by Modified MOCVD with Substrate Temperatures

Thermoelectric bismuth telluride () films were deposited on off oriented (001) GaAs substrates using a modified metal organic chemical vapor deposition (MOCVD) system. The effects of substrate temperature on surface morphologies, crystallinity, electrical properties and thermoelctric properties were investigated. Two dimensional growth mode (2D) was observed at substrate temperature lower than . However, three dimensional growth mode (3D) was observed at substrate temperature higher than . Change of growth mechanism from 2D to 3D was confirmed with environmental scanning electron microscope (E-SEM) and X-ray diffraction analysis. Seebeck coefficients of all samples have negative values. This result indicates that films grown by modified MOCVD are n-type. The maximum value of Seebeck coefficient was -225 and the power factor was at the substrate temperature of . films deposited using modified MOCVD can be used to fabricate high-performance thermoelectric devices.

Growth of Large Scale CdTe(400) Thin Films by MOCVD

We have investigated growth of CdTe thin films by using (As, GaAs) buffer layers for application of large scale IR focal plane arrays(IFPAs). Buffer layers were grown by molecular beam epitaxy(MBE), which reduced the lattice mismatch of CdTe/Si and prevented native oxide on Si substrates. CdTe thin films were grown by metal organic chemical deposition system(MOCVD). As a result, polycrystalline CdTe films were grown on Si(100) and arsenic coated-Si(100) substrate. In other case, single crystalline CdTe(400) thin film was grown on GaAs coated–Si(100) substrate. Moreover, we observed hillock structure and mirror like surface on the (400) orientated epitaxial CdTe thin film.

Growth of Nano Structure Bi 2 Te 3 Films using Modified MOCVD Technique

Nano structure films were deposited on (100) GaAs substrates using a modified MOCVD system and the effect of growth parameters on the structural properties were investigated. Different from conventional MOCVD systems, our reactor consist of pressure control unit and two heating zones ; one for formation of nano-sized particles and the other for the growth of nano particles on substrates. By using this instrument we successfully grow films with nano-grain size. The film grown at high reactor pressure has large grain size. On the contrast, the grain size decreases with a decrease in pressure of the reactor. Here, we introduce new growth methods of nano-grain structured films for high thermoelectric figure of merit.

Microstructures and Thermal Properties of Water Quenched Thermoelectric Material in Bi2Te3-PbTe System

In order to design nano structured materials with enhanced thermoelectric properties, the alloys in the pseudo-binary Bi2Te3-PbTe system are investigated for their micro structure properties. For this synthesis, the liquid alloys are cooled by the water quenching method. Micro structure images are obtained by using an electron probe micro analyzer(EPMA). Dendritic and lamellar structures are clearly observed with the variation in the composition ratio between Bi2Te3 and PbTe. The increase in the Bi2Te3 composition ratio causes to change of the structure from dendritic to lamellar. The Seebeck coefficient of sample 5, in which the mixture rate of Bi2Te3 is 83%, is measured as the highest value. In contrast, the others decrease with the increase of the Bi2Te3 composition ratio. Meanwhile, p-type characteristics are observed in sample 6, at 91%-Bi2Te3 mixture rate. The power factors of the all samples are calculated with the Seebeck coefficient and resistivity.

Effect of Hg-ambient annealing on Hg 0.7 Cd 0.3 Te thin films for IR detector

The liquid phase epitaxy(LPE) method was widely used to growth of mercury cadmium telluride(MCT) thin films. However, this method lead to Hg-vacancies in MCT thin film, because Hg has high vapor pressure at this temperature range. This is a well known defect in HgCdTe grown by LPE method. In this study, we report the development of techniques for improving the crystalline quality and controlling the composite uniformity of HgCdTe thin films using high- pressure Hg-ambient annealing method. As a result, we achieved the improvement of the composite uniformity of HgCdTe thin films. It was observed by the high angle annular dark field scanning TEM(HAADF-STEM) analysis. Moreover, new HgTe phase and a shrinking of lattice fringe were observed.