Young-Gu Jin

First-principles study of the compensation mechanism in N-doped ZnO

Abstract Based on first-principles electronic structure calculations for N-related and native point defects in Zinc Oxide (ZnO), we propose a mechanism for the compensation of N acceptors. As compared to a normal N2 source, the use of an active plasma N2 gas generally increases the N solubility limit, because the N chemical potential is enhanced. However, whenever a pure N source is used, N acceptors are greatly compensated by donor defects, which may explain the difficulty in achieving low-resistance p-type ZnO. Major compensating donors for N acceptors are found to be different at low and high N doping levels, and also depend on the type of N2 gas source.

Real-space electronic structure calculations of charged clusters and defects in semiconductors using a multigrid method

Abstract We present an efficient real-space multigrid method for first-principles electronic structure calculations, based on the pseudopotential method within the local-density-functional approximation. The Poisson and Kohn-Sham equations are accurately discretized by a higher-order finite difference method, and solved efficiently by a multigrid technique, which uses different relaxations for different sets of real-space grids. Testing various systems, we find the convergence to be nearly independent of the number of real-space grids. We demonstrate that our method is very useful for charged clusters and defects in localized bulk systems.

Stability and vibrational modes of H2 and H2∗ complexes in Si

Abstract We investigate the stability and local vibrational properties of H2 and H 2 ∗ complexes in Si through first-principles pseudopotential calculations within the local-density-functional approximation (LDA) and the generalized gradient approximation (GGA). We find the energy difference between H2 and H 2 ∗ to be less than 0.05 eV per H atom, testing supercells containing up to 216 atoms. For the [1 0 0], [1 1 0] , and [1 1 1] orientations of the H2 molecule at or near a tetrahedral site, the vibrational frequencies by the GGA for the stretch mode lie in the range of 3556– 3643 cm −1 , close to the experimental value of 3618 cm −1 , while they are underestimated by about 300 cm −1 in the LDA. A new local mode at 650– 700 cm −1 is predicted for the H2 molecule.

Local vibrational modes of H2 and H2* complexes in crystalline Si

We study the local vibrational properties of H2 molecules in crystalline Si using a first-principles pseudopotential method within the local-density-functional approximation and the generalized gradient approximation. The dynamical matrix is calculated using a supercell geometry, so that all the normal vibrational modes are identified for the [100], [110] and [111] orientations of the H2 molecule at or near a tetrahedral site. For the orientations considered here, a new local mode is found at 650-700 cm-1, which lies above the bulk phonon band, while the vibrational frequencies of the stretch mode are in the range of 3556-3643 cm-1, close to the experimentally measured value of 3618 cm-1. However, considering anharmonic effects, the calculated frequencies for the stretch mode are expected to be lowered by about 200 cm-1. We also examine the vibrational frequencies for an H2* complex, and find the stretch and wagging modes to be in good agreement with experiments.

First-principles calculation of the Coulomb pseudopotential for the simple hexagonal phase of Si

We calculate the Coulomb pseudopotential for the simple hexagonal phase of Si at a pressure of 14 GPa using a full-dielectric-matrix approach within the local-density-functional approximation. With all of the screening effects such as the crystal potential, local-field, and exchange - correlation effects, the value of is estimated to be 0.104. Considering only the crystal potential effect, is found to be very close to that of a free-electron gas. The exchange - correlation effect on the electron dielectric response function decreases the dielectric screening, especially for large wave vectors, giving rise to an increase of , while the local-field effect which results from directional bonds slightly reduces .