• Korean Journal of Materials Research
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• v.23 no.7
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• pp.379-384
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• 2013

In order to produce size-controllable Ag nanoparticles and a nanomesh-patterned Si substrate, we introduce a rapid thermal annealing(RTA) method and a metal assisted chemical etching(MCE) process. Ag nanoparticles were self-organized from a thin Ag film on a Si substrate through the RTA process. The mean diameter of the nanoparticles was modulated by changing the thickness of the Ag film. Furthermore, we controlled the surface energy of the Si substrate by changing the Ar or $H_2$ ambient gas during the RTA process, and the modified surface energy was evaluated through water contact angle test. A smaller mean diameter of Ag nanoparticles was obtained under $H_2$ gas at RTA, compared to that under Ar, from the same thickness of Ag thin film. This result was observed by SEM and summarized by statistical analysis. The mechanism of this result was determined by the surface energy change caused by the chemical reaction between the Si substrate and $H_2$. The change of the surface energy affected on uniformity in the MCE process using Ag nanoparticles as catalyst. The nanoparticles formed under ambient Ar, having high surface energy, randomly moved in the lateral direction on the substrate even though the etching solution consisting of 10 % HF and 0.12 % $H_2O_2$ was cooled down to $-20^{\circ}C$ to minimize thermal energy, which could act as the driving force of movement. On the other hand, the nanoparticles thermally treated under ambient $H_2$ had low surface energy as the surface of the Si substrate reacted with $H_2$. That's why the Ag nanoparticles could keep their pattern and vertically etch the Si substrate during MCE.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.3
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• pp.143-147
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• 2017

To evaluate surface characteristics and improve crystalline quality of AlN single crystal grown by physical vapor transport (PVT) method, wet chemical etching process using $KOH/H_2O_2$ mixture in a low temperature condition and thermal annealing process was proceeded respectively. Conventional etching process using strong base etchant at a high temperature (above $300^{\circ}C$) had formed over etching phenomenon according to crystalline quality of materials. When it occurred to over etching phenomenon, it had a low reliability of dislocation density because it cannot show correct number of etch pits per estimated area. Therefore, it was proceeded to etching process in a low temperature (below $100^{\circ}C$) using $H_2O_2$ as an oxidizer in KOH aqueous solution and to be determined optimum etching condition and dislocation density via scanning electron microscope (SEM). For improving crystalline quality of AlN single crystal, thermal annealing process was proceeded. When compared with specimens as-prepared and as-annealed, full width at half maximum (FWHM) of the specimen as-annealed was decreased exponentially, and we analyzed the mechanism of this process via double crystal X-ray diffraction (DC-XRD).

• Korean Journal of Materials Research
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• v.3 no.2
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• pp.121-130
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• 1993

The GaP crystals were grown by synthesis solute diffusion method and its properties were investigated. High quality single crystals were obtained by pull-down the crystal growing ampoule with velocity of 1.75mm/day. Etch pits density along vertical direction of ingot was increased from 3.8 ${\times}{10^4}$c$m^{-2}$ of the first freeze to 2.3 ${\times}{10^5}$c$m^2$ of the last freeze part. The carrier concentration and mobilities at room temperature were measured to 197.49cc$m^2$/V.sec and 6.75 ${\times}{10^{15}}$c$m^{-3]$, respectively. The temperature dependence of optical energy gap was empirically fitted to $E_g$(T)=[2.3383-(6.082${\times}{10^{-4}}$)$T^2$/(373. 096+TJeV. Photoluminescence spectra measured at low temperature were consist with sharp line-spectra near band-gap energy due to bound-exciton and phonon participation in band edge recombination process. Zn-diffusion depth in GaP was increased with square root of diffusion time and temperature dependence of diffusion coefficient was D(Tl = 3.2 ${\times}{10^3}$exp( - 3.486/$k_{\theta}$T)c$m^2$/sec. Electroluminescence spectra of p-n GaP homojunction diode are consisted with emission at 630nm due to recombination of donor in Zn-O complex center with shallow acceptors and near band edge emission at 550nm. Photon emission at current injection level of lower than 100m A was due to the band-filling mechanism.