Suk-Il Yoon

Origin of hexagonal-shaped etch pits formed in (0001) GaN films

We report the origin of hexagonal-shaped etch pits generally observed by conventional wet etching processes on (0001) GaN-based films based on the investigation with transmission electron microscopy on GaN films after being etched with molten KOH. The origin of hexagonal-shaped etch pits is identified as nanopipes through careful characterization of abnormal contrast of nanopipe (open-core screw dislocation), “lobe contrast” of end-on edge and screw (full-core) dislocations, visible and invisible conditions of edge and screw dislocations. Consideration of energetics of these defects also suggests preferential etch pit formation at nanopipes because of much higher energy.

Thermal stability dependence on the stacking order and thickness ratio of the CoPt–TiO2∕CoCrPt–SiO2 stacked media

Thermal stability of the present CoCrPt–SiO2 media becomes a more critical issue as recording density steadily increases. In the present study, thermal stability of the stacked media composed of high Ku CoPt–TiO2 and normal Ku CoCrPt–SiO2 was studied by changing stacking order and thickness of each layer while keeping a constant total thickness. When the CoPt–TiO2 layer was placed under the CoCrPt–SiO2 layer, negative nucleation field and coercivity increased much more than those of the reverse stacking case. Thermal stability of the CoPt–TiO2 bottom group was superior to that of the CoCrPt–SiO2 bottom group when measured by a spin stand.

Determination of defect types of ZnSe-based epilayers by etch-pit configurations

Abstract Determination of defect types by etch-pit configurations was studied. A NaOH (30 mol%) etchant was found useful for etch-pit development on ZnSe-based epilayers grown on (001) GaAs. After etch-pit formation on the surface, Transmission Electron Microscopy (TEM) experiments were conducted. The etch-pits have been formed in three different configurations; regularly paired etch-pits in the horizontal direction, regularly paired etch-pits in the vertical direction and an array of single etch-pits in the 〈110〉 and 〈100〉 directions which result from Frank-type stacking faults, Shockley-type stacking faults and threading dislocation segments, respectively.