The interface in a binary single quantum-well (SQW) structure of ZnSe/CdSe, where CdSe less than one monolayer is sandwiched by ZnSe layers (submonolayer SQW), is characterized by means of photoluminescence scpectroscopy. The dependence of the energy, linewidth and intensity of excitonic emission from the submonolayer SQWs on the well thickness of CdSe is extensively investigated. The characteristics of the excitonic emission are interpreted in terms of alloy formation at the interface. It is clarified that the ZnCdSe alloy is formed at the interface in ZnSe/CdSe quantum well heterostructure.
Initial growth stages of Ge on Si (111) are studied from the viewpoint of intermixing of Si into the epitaxial Ge layer. Defect formation in the Ge islands was characterized by using moiré patterns taken by transmission electron microscopy (TEM). Ge islands are grown by MBE on Si(111) surfaces with an SPE-grown buffer layer, which is expected to prevent intermixing between the epitaxial Ge layer and the Si substrate. Anomalous Si incorporation into the Ge islands is analyzed by TEM moiré fringe analysis. Dislocations are visualized by means of extra 'half-lines' of the moiré fringes, and thus Burgers vectors are determined. Stacking faults are observed by a displacement of the fringe spacings Coalescence of the Ge islands and dislocation generation from the contact part of the islands are detected.
Micrometer-to manometer-scale microstructures of porous Si are investigated by using highresolution scanning electron microscope (SEM), optical microscope, photoluminescence microscope and high-resolution transmission electron microscope (TEM) with aid of photoluminescence spectrometer. SEM and TEM observations revealed that the micrometer-scale structures of porous Si changed greatly by changing the anodization conditions. In contrast to those structures, the nanometer-scale structures of porous Si consisted of several nm to several tens nm single crystalline Si particles surrounded by glass structure SiOx(H). Visible photoluminescence of porous Si seems to come from these fine particles. Correlation between particle size and wavelength of photoluminescence was observed. It is difficult to explain, however, the variations in wavelength of photoluminescence by simple electron confinement model in the three dimensional quantum well structure of particles.
We have studied the origin of the strong visible photoluminescence of nanometer-size Ge crystal lites in SiO2 glassy matrix. Spectroscopic analyses and electron microscopic studies show that the room-temperature visible photoluminescence comes from Ge crystallites of diameter of 4 nm or less. The structure of Ge crystallites of diameter of 4 nm or less differs from the diamond structure.