Optical properties of type-II InGaN/GaNAs QW light-emitting diodes are investigated by using the multiband effective mass theory. These results are compared with those of conventional InGaN/GaN QW structures. The type-II InGaN/GaNAs/GaN QW structure shows much larger spontaneous emission and optical gain than that of a conventional QW structure. This can be explained by the fact that, in the case of the type-II QW structure, the effective well width is greatly reduced. A type-II QW structure shows that the peak position at a high carrier density is similar to that (530 nm) at a low carrier density. On the other hand, in the case of a conventional QW structure, the peak position is largely blueshifted at a high carrier density.

Optical properties of staggered InGaN/InGaN/GaN quantum-well (QW) light-emitting diodes with Ga-and N-faces were investigated using the multiband effective mass theory. The staggered QW structure shows that the carrier density dependence of the transition wavelength is largely reduced compared to the conventional QW structure. On the other hand, the heavy-hole effective mass around the topmost valence band is almost unaffected by the polarity. The N-face staggered InGaN/InGaN/GaN QW structure has a greater spontaneous emission peak than the Gaface staggered InGaN/InGaN/GaN QW structure because the former has a larger matrix element than the latter. We expect the N-face staggered InGaN/InGaN/GaN QW structure to have improved characteristics compared with the Ga-face staggered InGaN/InGaN/GaN QW structure.

Electronic properties of InGaAs/GaAs strained coupled quantum dots (QDs) are investigated using the eight-band model as a function of structural parameters such as strain (or the indium composition), the radius of QD, the height of QD, and the distance between the QDs. For the conduction band, the eight-band model shows a significantly larger ground state energy than the four-or six-band model. In the case of the hole, the differences of the ground state energy between these models are less significant than those for the conduction band states. In the case of the QD with a small height l, it is shown that the transition energies are nearly independent of models. However, with increasing l, the eight-band model gives results different from those of the four-or six-band model and the difference of the transition energy between models increases gradually. Similar results are also observed for the QD radius dependence of the transition energy. The transition energy increases with the distance d between two adjacent dots in the z direction while the transition energy is a weak function of the lateral dot spacing L À 2R along the x and y directions.

Valence band structures with spin-orbit (SO) coupling of quantum wires (QWRs), are investigated using the multiband effective-mass theory by a calculation procedure based on a finite-element method (FEM). The results are also compared to those obtained by finite difference method (FDM) and obtained by FEM without SO coupling. We expect FEM and FDM methods to give similar results, but the FDM has a limitation in dealing with various quantum wire shapes. In the case of QWR with small strains, the SO coupling effect does not greatly change subband energies and the trends of the subband dispersions. On the other hand, in the case of QWR with large strains, the subband energies of all states including the first state are considerably affected by the SO coupling. The amplitudes of the heavy-hole and light-hole wave functions have nonzero mixings even at the zone center (ky=0) in contrast to the case of quantum wells. It is found that the matrix elements for the TE polarization greatly increase due to the SO coupling effect.

To integrate multiple functional devices on a chip, advances in epitaxial growth on heterosubstances are required. As one approach to achieve an epitaxial layer on an amorphous substrate, we developed a method of combined epitaxial growth using molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD). This two-stage combined growth can be used to grow a binary gallium nitride (GaN) on any thermally durable substances. The first MBE growth step provided us effective nucleation with uniform morphology. Meanwhile, the second MOCVD growth enabled improved crystalline quality. Detailed analysis at grain-to-grain and layer-to-layer interfaces was studied with high-resolution transmission electron microscopy (TEM) characterization. This study gives a deep understanding of the growth behavior, thereby supporting the demonstration of perfect single crystalline GaN, enabling the realization of optoelectronic GaN-based devices on amorphous layer.