2014, Vol.24, No.4

Journal of the Korean Crystal Growth and Crystal Technology 2023 KCI Impact Factor : 0.19

pISSN : 1225-1429 / eISSN : 2234-5078
https://journal.kci.go.kr/jkcgct

The hydride vapor phase epitaxy (HVPE) grown GaN samples to precisely measure the surface characteristicswas applied to a molten KOH/NaOH wet chemical etching. The etching rate by molten KOH/NaOH wet chemical etchingmethod was slower than that by conventional etching methods, such as phosphoric and sulfuric acid etching, which may bedue to the formation of insoluble coating layer. Therefore, the molten KOH/NaOH wet chemical etching is a betterefficient method for the evaluation of etch pits density. The grown GaN single crystals were characterized by using X-raydiffraction (XRD) and X-ray rocking curve (XRC). The etching characteristics and surface morphologies were studied byscanning electron microscopy (SEM). From etching results, the optimum etching condition that the etch pits were wellindependently separated in space and clearly showed their shape, was 410oC and 25 min. The etch pits density obtained bymolten KOH/NaOH wet chemical etching under optimum etching condition was around 2.45 × 106cm−2, which iscommercially an available materials.

Co-(0.7 wt%) and Pr-(2.0, 3.5 or 5.0 wt%) doped cubic zirconia (ZrO2 : Y2O3 = 50 : 50 wt%) single crystalsgrown by a skull melting method were heat-treated in N2 at 1150oC for 5 hrs. The brown colored as-grown single crystalswere changed into either dark brownish green, greenish blue and light green color after the heat treatment. Before and afterthe heat treatment, the YSZ (yttria-stabilized zirconia) single crystals were cut for wafer form (ø7.5 mm × t3 mm). The opticaland structural properties were examined by UV-VIS spectrophotometer and X-ray diffraction. Absorption by Co2+(≒589 nm:Γ8[4A2(4F)]→Γ8 +Γ7[4T1(4F)], ≒610 nm: Γ8[4A2(4F)]→Γ8[4T1(4F)], ≒661 nm: Γ8[4A2(4F)]→Γ6[4T1(4F)]) and Pr3+(≒450 nm:3H4 −3P2, ≒473 nm:3H4→3P1, ≒484 nm:3H4→3P0), change of ionization energy and lattice parameter were confirmed.

GaN nanorods were grown on the apex of GaN stripes by three dimensional selective growth method. SiO2mask was partially removed only on the apex area of the GaN stripes by an optimized photolithography for the selectivegrowth. Metallic Au was deposited only on the apex of the GaN stripes and a selective growth of GaN nanorods wasfollowed by a metal organic vapor phase epitaxy (MOVPE). We confirmed that the shape and size of the GaN nanorodsdepend on growth temperature and flow rates of group III precursor. GaN nanorods were grown having a taper shapewhich have sharp tip and triangle-shaped cross section. From the TEM result, we confirmed that threading dislocationswere rarely observed in GaN nanorods because of the very small contact area for the selective growth. Stacking faultswhich might be originated from a difference of the crystal facet directions between the GaN stripe and the GaN nanorodswere observed in the center area of the GaN nanorods.