Dong Wook Kwak

Full Surface Embedding of Gold Clusters on Silicon Nanowires for Efficient Capture and Photothermal Therapy of Circulating Tumor Cells

We report on rapid thermal chemical vapor deposition growth of silicon nanowires (Si NWs) that contain a high density of gold nanoclusters (Au NCs) with a uniform coverage over the entire length of the nanowire sidewalls. The Au NC-coated Si NWs with an antibody-coated surface obtain the unique capability to capture breast cancer cells at twice the highest efficiency currently achievable (~88% at 40 min cell incubation time) from a nanostructured substrate. We also found that irradiation of breast cancer cells captured on Au NC-coated Si NWs with a near-infrared light resulted in a high mortality rate of these cancer cells, raising a fine prospect for simultaneous capture and plasmonic photothermal therapy for circulating tumor cells.

Extended defect states of Ge/Si quantum dots using optical isothermal capacitance transient spectroscopy.

We investigated the hole emission processes of optically induced charges on the defect states and confined states of self-assembled Ge quantum dots (QDs) embedded in a p-i-n Si diode. Optical deep level transient spectroscopy (ODLTS) and optical isothermal capacitance transient spectroscopy (OICTS) were used to study the defect states in ten stacked Ge quantum dots. Using ODLTS and OICTS for QD-embedded samples, the peaks related to the defect states of Ge QDs could be classified distinctly; it was about 20-50 times higher in intensity than that for the bulk defect states. The charges emitted from the QD defect state were observed near 93 K, and the activation energy was calculated to be E(V)+177 meV. The defect state followed the logarithmic capture kinetics and the Arrhenius-determined apparent activation energy decreased in the band gap as the optical injection width increased. We suggest that Ge QD defect states in Si could exist as extended states.

Effect of Si Growth Temperature on Fabrication of Si-ZnO Coaxial Nanorod Heterostructure on (100) Si Substrate

The realization and application of optoelectronics, photonics, and sensing, such as in solar diode sensors and photodiodes, which are potentially useful from ultraviolet to infrared light sensing, is dramatically advanced when ZnO is integrated into semiconductor nanostructures, especially when compatible with mature silicon technology. Here, we compare and analyze the fundamental features of the Si-ZnO coaxial nanorod heterostructures (Si@ZnO NRs) grown on semi-insulating (100)-oriented Si substrates at growing temperatures of 500°C, 600°C, 650°C, and 700°C of the Si layer for device applications. ZnO NRs were grown by a vapor phase transport, and Si layers were made by rapid thermal chemical vapor deposition. X-ray diffraction, field emission scanning electron microscopy (FESEM), energy-dispersive x-ray spectroscopy, and Raman experiments showed that ZnO NRs were single crystals with a würtzite structure, while the Si layer was polysilicon with a zincblende structure. Furthermore, FESEM revealed that Si shell thickness of the Si@ZnO NRs increases with increasing growing temperatures of Si from 500°C to 700°C.

Nitrogen effect on negative fixed charges of Al 2 O 3 passivation film in crystalline Si solar cells

We demonstrated the electrical evolution of the AlO, AlN, and AlON and the nitrogen (N) effect on negative fixed charges, which is responsible for the reduced positive charge traps of Al2O3 passivation films in crystalline Si solar cells. The AlO and AlN deposited by RF sputtering system were served as reference samples, and the AlON prepared by a nitrogen plasma exposure was served as controlled sample. The electrical properties of these samples were demonstrated through high-low (HL) capacitance-voltage (C-V) of metal-insulator-semiconductor (MIS) and photo-induced current transient spectroscopy (PICTS) to investigate interface and bulk defect states in the insulating films. 1MHz C-V curves of AlO, AlN, and AlON films, in which flatband voltage shifts (VFB) are around −0.55, −2.8 and 3.6 V, respectively. It reveals that the positive shift takes place as compared to the others and negative fixed charges are dominant in the AlON film. It was observed that defect states were decreased in the AlON film, and especially the defect state of 0.42 eV approximately disappeared. From the HL C-V measurement, the positive interface state was reduced in density from 2.15 × 1012 to 1.26 × 1010 cm−2. It is suggested that the dominant negative fixed charges in the AlON film result from the nitrogen effect and that nitrogen atoms in the AlON film take positive charge traps to be passivated.

Suppression of deep level defects in CIGS solar cells using proton implantations

The suppression effect on deep level defects and the defect generation in Cu(InGa)Se2 solar cells by a proton implantation have been investigated using deep level transient spectroscopy(DLTS) and optical DLTS measurements. CIGS films with the thickness of ∼3µm were grown on a soda-lime glass as substrate by co-sputtering method and implanted by proton with 2× 1016 cm−3 dose and in 50keV energy, and post-annealed under various conditions. To study the proton effect on deep level defects in CIGS films, DLTS and ODLTS were carried out and 5 hole traps and 3 electron traps were found. The calculated trap energies and densities for observed traps were summarized. After proton implantation and post annealing at 200°C for 5 min in N2 ambient, the deep defects which is known to attribute to loss of the CIGS solar cell efficiency were remarkably reduced in intensity. Therefore, we report that electrical deep level defects in CIGS films can be passivated by proton implantation and post annealing and that a deep level defect with the activation energy of Ev+0.28 eV generates newly.

Analysis of Deep-Level Defects on Proton Implanted Polycrystalline Silicon Thin Films Using Photoinduced Current Transient Spectroscopy

Photoinduced current transient spectroscopy was used to investigate the defect states and capture kinetics of charge carriers for traps in low temperature polycrystalline silicon (poly-Si) films. A broad deep trap was found to be located 0.30 eV from the conduction band edge of poly-Si with capture cross section of 1.51×10-15 cm2. The variation of the trap capture kinetics with filling pulse time showed extended traps and linear arrays of traps, which might be grain boundary defects. Proton implantation and H-plasma treatment were used to improve poly-Si device characteristics, with traps more effectively suppressed by the former treatment. The ionized hydrogen atoms implanted into the poly-Si films are imputed to amorphize the defective poly-Si film with post-annealing enhancing re-crystallization, resulting films with fewer defects.

Re-trapping process of charge traps in non-volatile memory with ONA structures

To investigate the charge trapping behavior in Oxide-Nitride-AI2O3 (ONA) structures, time-resolved photo-depopulation (TRPD) was introduced with varying the temperature and the photon energy. ONA structures were fabricated with the thickness of 3 nm (tunneling), 7 nm, and 10 nm (blocking), respectively. Tunneling oxide was grown by thermal oxidation while nitride and Al2O3 layers were deposited by low pressure chemical vapor deposition (LPCVD) and atomic layer deposition (ALD). All the measurements were carried out using real time with a spectrometer and an electrometer in the temperature ranges from 10 K to 300 K .

Morphological Evolution of Silicon Nanowires Grown by Chemical Vapor Deposition

Morphological evolution of Si nanowires (Si-NWs) grown on Si (001) substrates is explored. The Si-NWs are fabricated by nanoscale Au-Si island-catalyzed rapid thermal chemical vapor deposition. The Au-Si islands (10-50 nm in dia.) are formed by deposition of Au thin film (1.2-3.0 nm) at room temperature and followed by annealing at 700oC. The Si-NWs are grown by exposure them to a mixture of gasses of SiH4 and H2. We found a critical thickness of the Au film for Si-NW nucleation at a given growth condition. Also, we observed variation in the growth rate and the dimension of the NWs depending on the growth pressure and temperature. The resulting NWs are ~30-100nm in diameter and ~0.4-5.0μm in length. Most of the NWs were aligned along the <111> direction. The morphological and dimensional evolution of the Si-NWs is discussed in terms of kinetics (atomic diffusion mechanism) and energetics (surface and interface energies).