S. W. Lee

Bio: S. W. Lee is an academic researcher. The author has contributed to research in topics: Electron mobility & Epitaxy. The author has an hindex of 1, co-authored 1 publications receiving 23 citations.

Impact of V/III ratio on electrical properties of GaN thick films grown by hydride vapor-phase epitaxy

Abstract: Impact of V/III ratio on electrical properties of GaN thick films are investigated, which are grown by hydride vapor-phase epitaxy. The authors note that the electron concentration of GaN films decreases with the increase of V/III ratio, while their electrical resistivity and electron mobility increase simultaneously. These indicate that enhancing V/III ratio suppresses electron-feeding sources in GaN films, which is not by generating electron-trapping centers but by reducing donor-type defects. On the other hand, it is shown that the linewidth of x-ray rocking curves in GaN films decreases and the near-band edge emission intensity of 10K photoluminescence spectra increases as V/III ratio increases. These mean that higher V/III ratio condition helps for reducing crystalline point defects in GaN films. In terms of theoretical fitting into the temperature-dependence curves of electron mobilities, it is found that the electron transport of GaN films grown in lower V/III ratio condition is more hampered by de...

Simulation of high angle annular dark field scanning transmission electron microscopy images of large nanostructures

Abstract: High angle annular dark field scanning transmission electron microscopy (HAADF-STEM) is a powerful tool to quantify size, shape, position, and composition of nano-objects with the assessment of image simulation. Due to the high computational requirements needed, nowadays it can only be applied to a few unit cells in standard computers. To overpass this limitation, a parallel software (SICSTEM) has been developed. This software can afford HAADF-STEM image simulations of nanostructures composed of several hundred thousand atoms in manageable time. The usefulness of this tool is exemplified by simulating a HAADF-STEM image of an InAs nanowire.

Investigation of the crystallinity of N and Te codoped Zn-polar ZnO films grown by plasma-assisted molecular-beam epitaxy

Abstract: We report on the crystallinity, N incorporation efficiency, optical properties, and electrical properties of N and Te codoped ZnO films grown by plasma-assisted molecular-beam epitaxy. Te improves the surface morphology and roughness of ZnO films in terms of both streak reflection high energy electron diffraction pattern and atomic force microscopy observations. Also, N and Te codoping is helpful to improve the crystallinity and N incorporation efficiency simultaneously. We found that; (a) narrower x-ray linewidth and higher N concentration were obtained by codoping. (b) Nitrogen related emission lines including donor-acceptor pair and acceptor-bound exciton dominantly emerged in photoluminescence spectra. (c) Codoping enhanced the carrier compensation of native donors in ZnO films and suppressed the dislocation scattering. As a consequence, we concluded that N and Te codoping is very effective for the growth of reliable p-type ZnO films which fulfill the controversial requirements; high N concentration a...

Influence of heat treatments on electrical properties of ZnO films grown by molecular-beam epitaxy

Abstract: We report on the influence of heat treatments on the electrical properties of ZnO films grown by molecular-beam epitaxy. We note that the electrical resistance of the ZnO films is significantly changed by the heat treatments: the electrical resistance increases with the increase of ambient temperature, but above a critical temperature the resistance decreases with the increase of temperature, irrespective of ambient gases. On the other hand, it is found that the large amount of photocurrent is generated in the ZnO films, exposed to white sources: the photocurrent decreases with the increase of the obtained resistance, and the current increases with the decrease of the resistance. Also, it is shown that the x-ray diffraction linewidth of the ZnO films is significantly decreased by the heat treatments. These indicate that the increase/decrease of the electrical resistance is ascribed to the annihilation/formation of the residual donor-type defects in the ZnO films by the heat treatments. It is suggested tha...