Epitaxial growth and mechanism are reviewed. The epitaxial growth could be classified into four categories based on crystalline structure and lattice constant: homoepitaxy, quasi-homoepitaxy, quasi-heteroepitaxy, and heteroepitaxy. Particularly, the epitaxial growth methods for HI-V semiconductors are briefly described concerning with their advantage and disadvantage in growth. Further, unique technologies for the epitaxial growth are summarized. The initial growth modes of the epitaxy are introduced. The criterions for the modes are given in terms of the saturation degree, bonding energy, and adsorption energy. The calculation of strain energy in an intial hetero-epitaxial grown layer using valence-force-field method is introduced as an example of a microscopic analysis. The critical thickness calculated by the microscopic analysis is thinner than that by a continuum macroscopic analysis. The results agree well with the experimental thicknesses. It would give the approach to reveal the heteroepitaxial growth mechanism with an atomic scale.
The growth process for stress reduction in GaAs epilayers grown on Si (100) by molecular beam epitaxy was studied. The GaAs buffer layers were grown at 250℃ on misoriented Si(100) substrates (0〜6°off) with various thickness (0.05〜0.20μm), and then annealed at various temperatures (300〜600℃). The GaAs overlayers were sequentially grown at 300℃. In this process, the misfit dislocation density in the GaAs epilayer was controlled in the buffer layer formation process by changing the buffer layer thickness, the buffer layer annealing temperature and the off-angle of Si substrate, and the density was quenched during overlayer growth. The minimum-stressed GaAs epilayer was grown on 3°-off substrate with a 0.1 μm-thick buffer layer annealed at 500℃. In addition, the asymmetric stresses were observed between  and [01^^-1]. This asymmetry is caused by the difference in dislocation velocities or dislocation nucleation energies between α- and β-dislocations. The crystalline quality of GaAs epilayer should be improved in the low-stressed conditions.
Si heteroepitaxial layers were grown on InP (100) substrates by molecular beam epitaxy. The initial growth process of Si/InP was investigated by the in-situ observations of the reflection high energy electron diffraction (RHEED). During the Si growth, a (3×1) streaky pattern appeared and two-dimensional growth mode occurred up to 2 monolayers (ML) thick growth. With further growth, the RHEED internsity oscillations disappeared although the (3×1) streaky pattern was maintained up to 〜10 ML. A surface segregation of In atoms during the Si growth was observed by secondary ion mass spectroscopy. From these results, we proposed a model for the initial growth process of the Si on InP heteroepitaxy.
The role of an AlN buffer layer used to obtain uniform and high-quality GaN in the heteroepitaxial growth by MOVPE on sapphire (α-Al_2O_3) substrates has been studied. The initial growth processes of GaN grown with and without the A1N buffer layer shown by SEM images, and the GaN/AlN/sapphire interface is observed by cross sectional TEM images. The crystalline structure of GaN near the AlN interface reveals that the geometric selection of columnar GaN crystals causes the arrangement of the crystalline direction which results in the improvement of the crystalline quality. In the case without the AlN buffer layer, three dimensional island growth occurs; but in the case with the AlN buffer layer, three dimensional growth is converted to two dimensional growth, I. E. layer-by-layer growth after the smooth coalescence of the islands.
Preferred orientation (fiber texture) or epitaxial orientation was controlled using ZnO film with 3 dimensional covalent bond, (Ca, Sr) CuO_2 with 2 dimensional covalent bond, and LiNbO_3 (LiTaO_2) with ionic bond. For ZnO film, (0001), (112^^-0), and (1010) films were obtained on glass. For (Ca, Sr)CuO_2, (001) and (101) films were ob-tained on glass, (110) and (101) were obtained on (100) MgO. On R-cut sapphire, the orientation of the LiNbO_3 film changed from (011^^-2) to (101^^-0) via (112^^-0) by increasing the Li concentration in the film. Furthermore, the concepts to control these textures were proposed.
Blue and green lasers have been made from ZnSe-based II-VI compounds. These laser wafers are grown by only molecular beam epitaxy (MBE), since successful doping techniques have been obtained in MBE process. Low-resistivity n- and p-type ZnSe was accomplished with Cl doping and nitrogen radical doping, respectively. MBE growth of n-type ZnSe: Cl and p-type ZnSe: N, and optical and electrical properties of these layers are described. Recent advances in znSe-based lasers are also reported.
Morphologies of orderig domains or grains in the first order phase transition are numerically investigated under inhomogeneous external conditions. Morphology found by the homogeneous quenching is isotropic, I.e., irregular. When the quenching is inhomogeneous, morphologies are more or less regular. However, the regular morphology is not a simple reflection of the inhomogeneous external condition, but the morphology may change discontinuously.