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Well-aligned GaN nanorods were synthesized on Si substrates to form heterojunctions with potential applications in photovoltaic (PV) cells. Transmission electron microscopy images, selected area electron diffraction pattern images, and photoluminescence spectra showed that the GaN crystalline nanorods were preferentially oriented along the [0 0 0 1] direction and were very well-aligned perpendicular to the Si (1 1 1) substrate. An ultraviolet (UV) PV cell based on GaN nanorod/n-Si heterojunctions was fabricated, and current–voltage curves under an illumination with UV light exhibited obvious PV effect with a power conversion efficiency of about 1%.

X-ray diffraction patterns, scanning electron microscopy images, and transmission electron microscopy (TEM) images showed that one-dimensional GaN nanorods grown on Si (1 1 1) substarates by using hydride vapor phase epitaxy had crystalline wurzite structures and were preferentially oriented along the [0 0 0 1] direction. The high-resolution TEM (HRTEM) images showed that the side facet planes of the tip region for the GaN nanorods consisted of {1¯ 1 0 0}, {1¯ 1 0 2}, and {1¯ 1 0 3} planes. The structural properties of the GaN nanorods were significantly affected by the gas-mixing and the substrate temperatures in the final growth zone.

X-ray diffraction (XRD) patterns, field-emission scanning electron microscopy (FESEM) images, transmission electron microscopy (TEM) images, and selected area electron diffraction pattern (SADP) images showed that one-dimensional GaN nanorods with c -axis-oriented single-crystalline wurzite structures were grown on Si (1 1 1) substrates by using improved hydride vapor phase epitaxy. The high-resolution TEM (HRTEM) images showed that the crystallized GaN nanorods contained very few defects. The atomic arrangements for the GaN nanorods grown on the Si (1 1 1) substrates are described on the basis of the XRD, the TEM, the SADP, and the HRTEM results.

Dependence of the magnetic properties on the Mn/In flux ration in multiple stacked self-assembled (In 1− x Mn x )As quantum dots (QDs) was investigated. Transmission electron microscopy images showed that crystalline (In 0.84 Mn 0.16 )As QDs with symmetric single-domain particles were formed on GaAs substrates. Magnetic force microscopy (MFM) images showed that the density of the (In 1− x Mn x )As QDs decreased with increasing Mn/In flux ratio, and the magnetization curves as functions of the magnetic field at 5 K depicted that the magnetization of the (In 1− x Mn x )As QDs increased. Near-field scanning optical spectroscopy spectra for the (In 0.84 Mn 0.16 )As stacked QDs showed the interband transitions from the ground electronic subband to the ground heavy-hole band, indicative of the semiconductor phase of the QDs. These results indicate that magnetic properties of (In 1− x Mn x )As QDs are affected by the Mn/In flux ratio.

We have studied growth of self-assembled CdTe quantum dots (QDs) grown on various thicknesses of ZnTe buffer layer by using molecular beam epitaxy (MBE) and atomic layer epitaxy (ALE). The excitonic peak corresponding to the interband transitions from the ground electronic subband to the ground heavy-hole band (E1−HH1) in the CdTe/ZnTe QDs shifted to a lower energy with increasing thickness of the ZnTe buffer layer. The results of the atomic force microscopy (AFM) images showed that the size of the CdTe/ZnTe QDs increases with increasing thickness of the ZnTe buffer layer. The activation energy of the electrons confined in the CdTe/ZnTe QDs, as obtained from the temperature-dependent PL spectra, increases with increasing thickness of the ZnTe buffer layer. These results can help improve our understanding of the effect of the ZnTe buffer layer on the structural and the optical properties of CdTe/ZnTe QDs.

We have studied structural and optical properties of self-assembled Cd 0.6 Zn 0.4 Te/ZnTe quantum dots (QDs) grown on Si(1 0 0) substrates by using molecular beam epitaxy. X-ray diffraction patterns indicated that the ZnTe buffer layers grown on the Si substrates were hetero-epitaxial films with the (1 0 0) orientation. The atomic force microscopy images showed that Cd 0.6 Zn 0.4 Te/ZnTe QDs were formed on Si(1 0 0) substrates. The photoluminescence spectra at 32 K showed the dominant excitonic peaks corresponding to the interband from the ground-state electronic sub-band to the ground-state heavy-hole band in the Cd 0.6 Zn 0.4 Te/ZnTe QDs. The present results can help to improve the understanding of the structural and interband transition properties in Cd 0.6 Zn 0.4 Te/ZnTe QDs grown on Si(1 0 0) substrates.

Hexagonal MnAs thin films were grown on GaAs (1 0 0) substrates by using molecular beam epitaxy. The magnetization curve as a function of the magnetic field at 5 K showed that the MnAs thin films were ferromagnetic, and the magnetization curve as a function of the temperature revealed that the ferromagnetic transition temperature was as high as 318 K. The selected-area electron-diffraction pattern (SADP) and the high-resolution transmission electron microscopy (HRTEM) measurements on the MnAs/GaAs heterostructure showed that the hexagonal MnAs layer was grown pseudomorphically on the GaAs substrate. Based on the SADP and HRTEM results, a possible crystal structure for the MnAs/GaAs heterostructure is presented.

Atomic force microscopy (AFM) measurements were carried out to investigate the formation of CdTe quantum dots (QDs) grown on GaAs substrates by using molecular beam epitaxy. The AFM images showed that uniform CdTe QDs were formed on GaAs substrates due to the large lattice mismatch between the CdTe QDs and the GaAs substrate. The size and the density of the CdTe QDs were varied by changing the thickness and the substrate temperature. The formation behavior for the CdTe QDs on the GaAs substrate is in reasonable agreement with a Volmer–Weber (V–W) growth mode. The size and the density of the CdTe QDs grown on the GaAs substrate by using the V–W growth mode are compared with those of the CdTe QDs grown on the ZnTe buffer layer by using the Stranski–Krastanow mode. The present results can help improve understanding of the formation and the structural properties of CdTe QDs directly grown on GaAs substrates.

Photoluminescence (PL) and transmittance measurements were carried out to investigate the optical properties of ZnO nanoparticles inserted into ultraviolet (UV) opal. The ZnO nanoparticles were grown in the voids between face-centered cubic packed silica spheres by using a chemical deposition. The PL spectra showed a decrease in the band edge emission and an enhancement of the deep-level emission from the ZnO nanoparticles embedded in the UV opal. The PL intensity enhancement in the green spectral region might be attributed to the Purcell effect. The infiltration of ZnO nanoparticles inside an artificial opal can be used to select the spectral band and to increase the emission efficiency of ZnO nanoparticles.

Reflection high-energy electron diffraction, atomic force microscopy, and transmission electron microscopy measurements were used to investigate the dependences of the formation process and the strain variation on the As 4 /In ratio and the substrate temperature in InAs/GaAs quantum dots (QDs) grown by using molecular beam epitaxy. The variations of the lattice constants of the InAs wetting layer and the InAs QDs were significantly affected by the As 4 /In ratio and the growth temperature. The magnitude in strain of the InAs QDs formed at a low substrate temperature was larger than that in InAs QDs grown at high substrate temperature. The present results can help to improve the understanding of the formation process of defect-free InAs QDs.

The effect of In x Ga 1− x As ( x = 0.1 , 0.2) asymmetric strain release layers (ASRLs) on the microstructural and the interband transition properties of InAs/GaAs quantum dots (QDs) grown by using molecular beam epitaxy (MBE) and atomic layer epitaxy was investigated by using high-resolution transmission electron microscopy (HRTEM) and photoluminescence (PL) measurements. When the thickness of the ASRL covering the QDs was increased in the range between 0 and 5 nm, the PL peak corresponding to the interband transitions shifted to longer wavelengths due to strain relaxation. However, when the thickness of the ASRL was increased above approximately 7 nm, the peak shifted to shorter wavelengths due to the local interdiffusion of In and Ga atoms between the In x Ga 1− x As capping layer and the InAs QDs as a result of the localized strains in the In x Ga 1− x As capping layer and the InAs QDs. These results provide important information on the tunable feasibility of the interband transitions in the InAs/GaAs QDs utilizing the In x Ga 1− x As capping layer.

The microstructural, optical, and magnetic properties of (Zn 1− x Mn x )O thin films grown on (0 0 0 1) Al 2 O 3 substrates by using a radio-frequency magnetron sputtering were investigated. X-ray diffraction, atomic force microscopy, and scanning electron microscopy measurements showed that the microstructural properties of the (Zn 1− x Mn x )O thin films were improved by increasing the thickness of the (Zn 1− x Mn x )O buffer layer, which might originate from the suppression of the columnar-growth mode at the initial growth stage because the (Zn 1− x Mn x )O buffer layer grown at a lower temperature had a relaxed c -axis preference. The photoluminescence peak at 419 nm from the (Zn 0.91 Mn 0.09 )O thin films could be attributed to the activation of Mn 2+ ions substituting for Zn 2+ ions, indicative of the existence of a diluted magnetic semiconductors. The magnetization curve as a function of the magnetic field at 15 K indicated that ferromagnetism existed in the (Zn 0.91 Mn 0.09 )O thin films, and the magnetization curve as a function of the temperature showed that the T c value of the (Zn 0.91 Mn 0.09 )O thin films was 110 K. These results can help improve understanding of the effects of the microstructural properties on the magnetic properties of (Zn 1− x Mn x )O thin films grown on (0 0 0 1) Al 2 O 3 substrates.

Thermal annealing effects on the magnetic properties of (Ga 1− x Mn x )As with various Mn mole fractions grown on GaAs (1 0 0) substrates by using molecular beam epitaxy were investigated. When thermal annealing was performed, the ferromagnetic transition temperature ( T C ) of the (Ga 1− x Mn x )As thin films increased. The increase in the T C originated from a decrease in the concentration of the Mn interstitial atoms or from an increase in the uncompensated Mn spin which contributed to the magnitude of the ferromagnetism. These results can help improve the understanding of the effect of thermal annealing on the magnetic properties of (Ga 1− x Mn x )As thin films grown GaAs substrates.

The annealing effect on the surface and the microstructural properties of ZnO thin films grown on p-Si (1 0 0) substrates by radio-frequency magnetron sputtering have been investigated using atomic force microscopy (AFM), X-ray diffraction (XRD), and transmission electron microscopy (TEM) measurements. The AFM images and the XRD patterns showed that the crystallinity of the annealed ZnO films was enhanced by annealing in comparison with that of the as-grown ZnO films, and XRD patterns, pole figures, and TEM images showed that the as-grown and the annealed ZnO films grown on Si (1 0 0) substrates had a c-axis preferential orientation in the [0 0 0 1] crystal direction. These results indicate that the surface and the microstructural qualities of the ZnO films grown on p-Si (1 0 0) substrates are improved by thermal treatment.

The dependence of the optical properties on the temperature in multiple-stacked InAs/GaAs quantum dots (QDs) grown on (0 0 1)-oriented GaAs substrates by using molecular beam epitaxy was investigated. The periods of the photoluminescence (PL) spectra at low temperature for the sample with a three-monolayer (ML) InAs seed layer and two 1.8-ML InAs layers showed doublet peaks. The double peaks originated from interband transitions from the ground state subband to the ground heavy-hole band for QDs with a bimodal size-distributation, which was verified by using transmission electron microscopy measurements. The temperature-dependent PL spectra are discussed in terms of the inhomogeneous size distribution of the QDs and the carrier repopulation process. The present results can help to improve the understanding of the dependence of the optical properties on the temperature in multiple-stacked InAs/GaAs QDs.

Atomic force microscope (AFM), transmission electron microscopy (TEM), and photoluminescence measurements were carried out to investigate the dependence of the InAs quantum dot size distribution on the stacked layer number for vertically stacked InAs/GaAs quantum dots (QDs) grown on (0 0 1) GaAs substrates. AFM and TEM images showed that the size of the QDs increased with increase in the stacked layer number up to the deposition time of 20 s. However, the size distribution uniformity of the QDs was improved with increase in the stacked layer number when the deposition time and the stacking layer of the InAs QDs gradually decreased. These results can help in an improved understanding of the control of sizes of QDs in InAs/GaAs QD arrays.

Binominal expressions for the reflection high-energy electron diffraction (RHEED) oscillations during the growth of thin films by molecular beam epitaxy (MBE) were investigated. The dependence of the RHEED oscillation shape on the molecular migration time and the oscillation period was analyzed quantitatively. The peaks and valleys in the calculated oscillation intensities as a function of the oscillation period were in qualitatively reasonable agreement with those obtained from the experimental data. These results can help in controlling the epitaxial film thickness in the growth of films by using the MBE technique.

High-quality epitaxial Gd x Y 1− x Ca 4 O(BO 3 ) 3 thin films were successfully fabricated on atomically flat GdCa 4 O(BO 3 ) 3 (0 1 0) single crystal substrates by laser molecular beam epitaxy from a sintered Gd x Y 1− x Ca 4 O(BO 3 ) 3 ( x =0.28) target. It was found that the film surface morphology strongly depends on the substrate temperature and the laser repetition rate. The film crystallinity was highly dependent of substrate materials. Second-harmonic generation (SHG) was observed on the epitaxial Gd x Y 1− x Ca 4 O(BO 3 ) 3 films grown on GdCa 4 O(BO 3 ) 3 (0 1 0) substrates.

ZnO thin films were grown on p-InP(1 0 0) substrates by using radio-frequency magnetron sputtering at low temperature (∼200°C). Atomic force microscopy images showed that the root mean square of the average surface roughness of the ZnO film was 17.2 A, and X-ray diffraction and transmission electron microscopy (TEM) measurements showed that the ZnO film layers grown on the InP substrates were epitaxial films with strong (0 0 0 1) preferential orientation. Auger electron spectroscopy and bright-field TEM measurements showed that the ZnO epitaxial films grown on InP substrates at 200°C had no significant interdiffusion problems. These results indicate that the ZnO epitaxial films grown on p-InP(1 0 0) substrates at low temperature, hold promise for new kinds of potential high-speed optoelectronic devices based on InP substrates, such as low-loss optical waveguides and high-efficiency solar cells and that the ZnO epitaxial films grown on p-InP(1 0 0) substrates can be used as promising buffer layers for the growth of the GaN-related epilayers.

Double-crystal X-ray rocking curve (DCXRC), transmission electron microscopy (TEM), secondary-ion mass-spectroscopy (SIMS), and Hall-effect measurements were performed in order to investigate the structural and the electrical properties of arsenic planar-doped Hg 1− x Cd x Te epilayers grown on Cd 0.96 Zn 0.04 Te (2 1 1) B substrates by molecular beam epitaxy. From the DCXRC analyses, the grown Hg 1− x Cd x Te layers were found to be very high-quality epitaxial films. The TEM measurements showed that high-quality Hg 1− x Cd x Te epitaxial layers with abrupt interfaces were grown on the Cd 0.96 Zn 0.04 Te substrates. A doping profile of the arsenic dopant was obtained from SIMS measurements. While all of the as-grown arsenic conventional-doped Hg 1− x Cd x Te epilayers were n-type, some of the arsenic planar-doped Hg 1− x Cd x Te thin films were p-type. These results indicate that the arsenic planar-doped Hg 1− x Cd x Te thin films hold promise for applications in infrared focal-plane array photodetectors and photodiodes.

Strain relaxation phenomena of the heteroepitaxial lattice-mismatched semiconductors have been investigated. The relationship between the residual in-plane strain and the width of the misfit cell was obtained geometrically. The residual in-plane strain was calculated for various film thicknesses by using the energy minimization theory on the misfit cell in the InxGa1−xAs/GaAs(1 0 0) heterostructure system. A generalized strain relaxation model is presented on the basis of the energy minimization theory.

A new approach has been introduced for the fabrication of Ag/p-InP(1 0 0) heterostructures by ion-beam-assisted deposition with the goal of growing Ag epitaxial films. X-ray diffraction measurements showed that the Ag thin-film layers grown on the InP substrates were polycrystalline. Auger electron spectroscopy measurements showed that the Ag was uniformly distributed throughout the thickness of the film and that a relatively sharp interface existed. Transmission electron microscopy showed that the grown Ag film was a polycrystalline layer and that an interfacial layer was formed in the Ag/InP heterointerface. These results indicate that the growth of polycrystalline Ag layers instead of epitaxial films originates from the formation of an interfacial amorphous layer prior to the creation of the films.

Several kinds of CdTe ZnTe strained single and double quantum well structures were grown on GaAs (100) substrates by the simple method of double-well temperature-gradient vapor-transport deposition. X-ray diffractometry and transmission electron microscopy measurements were performed to characterize the structural properties of the CdTe ZnTe quantum wells. Photoluminescence (PL) measurements on the CdTe ZnTe strained single quantum wells showed that the sharp excitonic peaks corresponding to the transitions from the first electronic subband to the first heavy-hole band were shifted to lower energy with increasing well width. The results for the PL data on the CdTe ZnTe double quantum wells at 15 K demonstrated clearly that the transition behavior from coupled to uncoupled peaks depends on the ZnTe embedded potential barrier thickness. Photoreflectance measurements showed several resonant excitations in the CdTe ZnTe single and double quantum wells. Electronic subband energies and wavefunctions were calculated by an envelope function approximation taking into account the strain effects, and the theoretical values of the interband transitions were in good agreement with those obtained from the experimental measurements. The coupling behavior between two CdTe wells separated by a ZnTe barrier layer in the double quantum wells investigated by theoretical calculations was in good qualitative agreement with those obtained from experimental data.

Photoluminescence (PL) measurements were performed in order to investigate the carbon impurity effects on the intermixing behavior of GaAs/AlAs multiple quantum wells (MQWs) grown by molecular beam epitaxy. The GaAs/AlAs MQWs were annealed with a carbon source in a furnace annealing system. The PL spectra show that the magnitude of the intermixing of Al and Ga induced by thermal annealing in GaAs/AlAs MQWs increases with depth. The nonuniformity of the intermixing as a function of the depth originated from the carbon impurities which were injected during thermal treatment.