Young Joon Cho

Enhanced boron gettering effect of n-type solar grade Si wafers by in situ oxidation

To investigate the gettering effect of n-type (phosphorous-doped) crystalline Czochralski-silicon (Cz-Si) wafers, we made boron emitters by diffusing boron into them and, subsequently, oxidized the boron-diffused n-type crystalline silicon wafers by in situ wet and dry oxidation. After oxidation, we measured the minority carrier lifetime by using microwave photoconductivity decay (μ-PCD), open-circuit voltage by quasi-steady-static photoconductance and the sheet resistance by a 4 point probe, respectively. We suggested the boron diffusion and in situ oxidation conditions to achieve longer lifetimes. We can obtain the equivalent lifetime to conventional oxidation through the quartz tube designed for boron doping and in-situ oxidation. The uniformity of sheet resistance under 3% was achieved at relatively low temperature and the lifetime of 21.6 μs was also obtained by boron gettering effect and passivation of oxide layer.

Accelerated phosphodiester cleavage of bis(p-nitrophenyl)-phosphate by receptors

Phosphodiester cleavage of BNPP can be accelerated by various degradative receptors including enzymes. In the hydrolytic cleavage of BNPP, a bell-shaped receptor concentration-rate profile composed of a positive-catalysis phase at low receptor concentrations and a negative-catalysis phase at excess receptor concentration was observed. The negative catalysis can be explained by nonproductive binding, leading to an increase of the activation energy barrier and a decrease of the reaction rate.

Accelerated hydrolysis of esters catalyzed by receptors, I nonenzymatic cleavage ofp-nitrophenyl acetate by polypeptides

The hydrolysis kinetics ofp-nitrophenyl acetate by basic polypeptides with a variety of amino acid residues were analyzed. The results suggest that the tertiary structure of microenvironment brought about by random coil assembly is more important as a binding site than the number of basic residues (catalytic sites).

결정질 실리콘 태양전지 적용을 위한 ALD-Al2O3 패시베이션 막의 산화질화막 적층 특성

Silicon oxynitride that can be deposited two times faster than general SiNx:H layer was applied to fabricate the passivation protection layer of atomic layer deposition (ALD) Al2O3. The protection layer is deposited by plasma-enhanced chemical vapor deposition to protect Al2O3 passivation layer from a high temperature metallization process for contact firing in screen-printed silicon solar cell. In this study, we studied passivation performance of ALD Al2O3 film as functions of process temperature and RF plasma effect in plasma-enhanced chemical vapor deposition system. Al2O3/SiON stacks coated at 400 oC showed higher lifetime values in the as-stacked state. In contrast, a high quality Al2O3/SiON stack was obtained with a plasma power of 400 W and a capping-deposition temperature of 200 oC after the firing process. The best lifetime was achieved with stack films fired at 850 oC. These results demonstrated the potential of the Al2O3/SiON passivated layer for crystalline silicon solar cells.

Atomic Layer Deposition of HfO₂ Films on Ge

We investigated the growth characteristics and interfacial properties of HfO₂ films deposited on Ge substrate through atomic layer deposited (ALD) by using an in-situ medium energyion scattering analysis. The growth kinetics of HfO₂ grown on a GeO₂/Ge substrate through ALD is similar to that grown on an SiO₂/Si substrate. However, the incubation period of HfO₂ deposition on Ge is shorter than that on Si. The HfO₂ grown on the GeO/Ge substrate shows a significant diffusion of Hf atoms into the substrate interface and GeO volatilization after annealing at 700℃. The presence of low-quality Ge oxide or suboxide may degrade the electrical performance of device.

Accelerated hydrolysis of esters catalyzed by receptors, II. Degradation of RNA by polyvinylpyrrolidone

The nonenzymatic hydrolysis of RNA by polyvinylpyrrolidone (PVP) has been investigated. A bell-shaped kinetics was observed when the first order rate constant of the reaction was ploted as a function of PVP concentration, which means the kinetic feature of PVP as a degradative receptor distinct from those of degradative enzymes (e.g., ribonuclease).