Cheol Woo Park

Investigation of defects and surface polarity in AlN and GaN using wet chemical etching technique

Division of Materials Science and Engineering, Hanyang University, Seoul 133-791, Korea*Unimo Photron Co., Ltd., Seoul 137-820, Korea(Received October 2, 2014)(Revised October 14, 2014)(Accepted October 17, 2014)Abstract We investigated defects and surface polarity in AlN and GaN by using wet chemical etching. Therefore, theeffectiveness and reliability of estimating the single crystals by defect selective etching in NaOH/KOH eutectic alloy havebeen successfully demonstrated. High-quality AlN and GaN single crystals were etched in molten NaOH/KOH eutecticalloy. The etching characteristics and surface morphologies were carried out by scanning electron microscope (SEM) andatomic force microscope (AFM). The etch rates of AlN and GaN surface were calculated by etching depth as a function ofetching time. As a result, two-types of etch pits with different sizes were revealed on AlN and GaN surface, respectively.Etching produced hexagonal pits on the metal-face (Al, Ga) (0001) plane, while hexagonal hillocks formed on the N-face.On etching rate calibration, it was found that N-face had approximately 109 and 15 times higher etch rate than the metal-face of AlN and GaN, respectively. The size of etch pits increased with an increase of the etching time and they tend tomerge together with a neighbouring etch pits. Also, the chemical mechanism of each etching process was discussed. It wasfound that hydroxide ion (OH

Fabrication of YAG : Er 3+ powders for the single crystal growth according to the synthetic temperature and flux concentration

In this study, using solid-state and flux, powders were successfully synthesized at low temperatures. To analyze the crystallinity of powders according to the synthesis or non-synthesis of powders and powder calcination temperatures, X-ray diffraction (XRD) was measured. In the case of pure YAG, when YAG was analyzed using the general solid-phase method, it was calcined for 12 hours at and pure YAG phase could be obtained. But when was added to YAG, YAG was synthesized at lower temperature (). It was thus found that the synthesis temperature could be lowered by about . Also, when BaF2 with an optimal concentration was added to , the particle shape and size according to synthesis temperatures were surveyed, and corresponding luminous intensity was discussed.

Wet chemical etching of molten KOH/NaOH eutectic alloy to evaluate AlN single crystal

We investigated the optimal etching conditions and properties of the surface change due to molten KOH/NaOH chemical wet etching using an AlN wafer which has been put to practical use in the present study. Results were observed using a scanning electron microscope after 5 minutes etching at 350 o C, was found to have a surface form of the respective other Al-face, the N-face. In particular, etch-pit in the form of a hexagon, which is observed in the Al-face appeared, It was calculated at 2 × 10 6 /cm 2 ~10 10 /cm 2 dislocation density. In the case of N-face, lattice defects in the form of the hexagonal pyramids is formed. It was discovered that in order to observe the orientation of the wafer, which corresponds to the Caxis direction of the resulting hexagonal AlN which was analyzed using XRD (0002) and is a state of being oriented in the (0004) plane. The Radius of curvature of AlN wafer was 1.6~17 m measured by DC-XRD rocking curve position.

The molten KOH/NaOH wet chemical etching of HVPE-grown GaN

Division of Materials Science and Engineering, Hanyang University, Seoul 133-791, Korea*UNIMO Photron, Seoul 137-063 Korea(Received June 10, 2014)(Revised July 7, 2014)(Accepted July 18, 2014)Abstract 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 410