Papers by Author: Tae Whan Kim

Abstract: The high-resolution scanning electron microscopy (HRSEM) image showed that selfassembled ZnSe small quantum dots (QDs) and large nanodots with a pyramid shape were formed in the Cl-doped ZnSe epilayers grown on GaAs (100) substrates. The formation of the ZnSe QDs was attributed to three-dimensional growth controlled by distribution of the impurities in the Cldoped ZnSe epilayrs. Cathodoluminescence (CL) measurements at room temperature revealed the emission peak at 3.1 eV corresponding to the blue shift approximately 400 meV from the near band edge emission of 2.7 eV in the bulk ZnSe. The blue shifted CL peak indicates the quantum confinement effect resulting from the formation of the ZnSe QDs in the Cl-doped ZnSe thin film. While the peak position of the donor-acceptor pair emission shifted to higher energies with decreasing temperature, the band-edge emission peak for the QDs did not significantly change.

Abstract: The X-ray diffraction (XRD) pattern for the ZnO films grown on Si (100) substrates indicates that the grown ZnO films have a strong c-axis orientation. The pole figure indicates that ZnO thin films have columnars with the grains of the [0002] crystallographic axis perpendicular to the Si (100) substrate, indicative of the random rotational orientations along the c-axis. Selected area electron diffraction pattern (SADP) of the ZnO/Si (100) heterostructures shows that the ZnO preferential oriented film is formed on the Si substrate. A possible atomic arrangement of the crystal structure and the formation mechanism of the c-axis orientated ZnO thin films grown on p-Si substrates are discussed on the basis of the XRD, the pole figure, and SADP results.

Abstract: Capacitance-voltage (C-V) and Deep-level transient spectroscopy (DLTS) measurements on AlxGa1-xN/GaN heterostructures were performed to investigate the existence of the carriers and the behavior of the deep levels in the AlxGa1-xN/GaN heterointerface. The C-V depth profile showed that the carrier concentration existed at the AlxGa1-xN/GaN heterointerface was 4 × 1012 cm2. The DLTS results showed two deep levels. The capture cross-section of the deep level related to the two-dimensional electron gas decreased with increasing depth, resulting from the existence of the different deep levels in each region.