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The electrical and optical properties of organic light-emitting devices (OLEDs) with bis(ethylenedithio)-tetrathiafulvalene (BEDT-TTF)-doped 4,7-diphenyl-1,10-phenanthroline (BPhen) electron transport layers (ETLs) were investigated. The current density–voltage characteristics of the OLEDs with BEDT-TTF-doped BPhen ETLs and electron only devices with BEDT-TTF-doped BPhen layers showed that the electrons injected from the cathode were increased by inserting a BEDT-TTF-doped BPhen layer. OLEDs containing BEDT-TTF-doped BPhen layers at a doping concentration of 1 wt.% demonstrated the highest current density and luminance values. Enhancements of the electron injection and luminance as well as a decrease in the operating voltage of the OLEDs were achieved by inserting a BEDT-TTF-doped BPhen layer.

The role of gain in an optical filter is advanced by good agreement between theory and experiment presented herein. The particular integrated photonic filter is composed of four semiconductor optical amplifiers and one four-port coupler located at the intersection of the amplifiers. The four-port coupler is realized using frustrated total internal reflection off a very thin slab of alumina embedded in the substrate. The delta function response of the filter is measured using an ultra-fast laser and cross-correlator, and the measured transfer functions agree well with a z-transform-based description of the device.

The electrical and optical properties of organic light-emitting devices (OLEDs) with three periods of 4,7-diphenyl-1,10-phenanthroline (BPhen)/aluminum tris(8-hydroxyquinolate) (Alq3) multiple heterostructures acting as an electron transport layer (ETL) were investigated. While the leakage current of OLEDs with multiple heterostructures was smaller than that of OLEDs without multiple heterostructures, the luminance efficiency was larger than that of OLEDs without multiple heterostructures. The BPhen layers in the multiple heterostructures blocked holes from the emitting layer (EML) to the ETL, and they enhanced the electron injection from the cathode to the EML, resulting in an increase in the luminance efficiency.

The electrical and optical properties of blue organic light-emitting devices (OLEDs) containing a mixed host emitting layer (EML) consisting of a 1,3-bis(carbazole-9-yl)benzene (mCP) layer and a 3-tert-butyl-9,10-di(naphtha-2-yl)anthracene (TBADN) layer were investigated. The driving voltage of the OLEDs with a mixed host EML was smaller than that of the OLEDs with a single EML. The electroluminescence spectra for OLEDs containing a mixed host EML showed a dominant peak related to the mCP or the TBADN layer. The color coordinates of the OLEDs containing a 5% TBADN-doped mCP EML were (0.146, 0.091), indicative of the deep blue color coordinates.

The effects of electric fields and temperatures on the carrier mobilities in organic layers and at electrode/organic interfaces were investigated by using three-dimensional Monte-Carlo simulation. The mobility variations in the organic layers and at the electrode/organic layer interfaces were described on the basis of the calculated results. The density of deep sites significantly affected the difference in the mobility behavior between the organic layers and the electrode/organic interfaces.

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%.

InGaP single-junction solar cells are grown on lattice-matched Ge-on-Si virtual substrates using metal-organic chemical vapor deposition. Optoelectronic simulation results indicate that the optimal collection length for InGaP single-junction solar cells with a carrier lifetime range of 2–5 ns is wider than approximately 1 μm. Electron beam-induced current measurements reveal that the threading dislocation density (TDD) of InGaP solar cells fabricated on Ge and Ge-on-Si substrates is in the range of 104–3 × 107 cm−2. We demonstrate that the open circuit voltage (Voc) of InGaP solar cells is not significantly influenced by TDDs less than 2 × 106 cm−2. Fabricated InGaP solar cells grown on a Ge-on-Si virtual substrate and a Ge substrate exhibit Voc in the range of 0.96 to 1.43 V under an equivalent illumination in the range of ∼0.5 Sun. The estimated efficiency of the InGaP solar cell fabricated on the Ge-on-Si virtual substrate (Ge substrate) at room temperature for the limited incident spectrum spanning the photon energy range of 1.9–2.4 eV varies from 16.6% to 34.3%.

While the current densities of hole only devices with a 2,3,5,6-tetrafluoro-7,7,8, 8-tetracyano-quinodimethane (F4-TCNQ) doped N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) hole transport layer (HTL) slightly changed with increasing F4-TCNQ doping concentration, those of hole only devices with a F4-TCNQ doped 4,4′,4″-tris(N-(2-naphthyl)-Nphenylamino)triphenylamine (2-TNATA) HTL significantly increased. The hole injection and hole transport of hole only devices were enhanced by inserting an ultra thin F4-TCNQ layer between an indium-tin-oxide layer and a NPB HTL or a 2-TNATA HTL, regardless of the HTL materials. These results indicate that the hole injection and hole transport in OLEDs utilizing a F4-TCNQ doped HTL or a F4-TCNQ thin layer is enhanced.

The luminance efficiency of the blue organic light-emitting devices (OLEDs) fabricated utilizing a double emitting layer (DEML) with a 4,4′-Bis(2,2-diphenyl-ethen-1-yl)diphenyl (DPVBi) layer doped with 4,4′-Bis[4-(diphenylamino)styryl]biphenyl (BDAVBi) fluorescence dopant and a 4,4′-Bis(carbazol-9-yl)biphenyl (CBP) layer doped with a bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl)iridium III (FIrpic) phosphorescence dopant at 20 mA/cm2 was 6.2 cd/A, indicative of highly efficient OLEDs. Electroluminescence spectra for the OLEDs with a DEML showed that a dominant peak at 469 nm corresponding to the BDAVBi doped DPVBi layer together with a shoulder at 491 nm related to the combination of the BDAVBi doped DPVBi layer and the FIrpic doped CBP layer appeared.

Top-emitting organic light-emitting diodes (TEOLEDs) with a thin semitransparent conducting cathode (STCC) of Ba∕Ag/indium tin oxide (ITO) were fabricated and their electric/optical characteristics were investigated. At the wavelength of 520nm, optical properties of STCC of the Ba(3nm)∕Ag(15nm)/ITO (100nm) structure showed the transmittance of 63% and the reflectance of 37%. The light out-coupling properties of the TEOLED, which is composed of glass/Ag(150nm)/ITO (130nm)∕4,4′,4″-tris[2-naphthylphenyl-1-phenylamino]triphenylamine (2-TNATA, 30nm)/4,4′-bis[N-(1-napthyl)-N-phenyl-amino]-biphenyl (18nm)/tris(8-quinolinolato)aluminum (III) (62nm)∕Ba (xnm,x=3,2,and1nm)∕Ag(15nm)/ITO (100nm), was increased as the deposition thickness of Ba is increased. This driving performance of the devices could be interpreted on the base of carrier injection barrier by measuring built-in voltage as well as both the optical properties and electric properties of the cathode. The optical properties (e.g., transmittance and reflec...

The influence of the presence of a double emitting layer (DEL) consisting of 4,4′-Bis(carbazol-9-yl)biphenyl (CBP) and 4,4′-Bis(2,2-diphenyl-ethen-1-yl)diphenyl (DPVBi) acting as electron and hole trapping layers in the organic light-emitting devices (OLEDs) was studied. While the luminance efficiency of the OLEDs with a DEL was very stable, regardless of variations in the applied voltage, that of the OLEDs with a CBP or a DPVBi emitting layer varied with the applied voltage. The rate of decrease is smaller than the single emitting layer, about 30%. The dominant peak corresponding to the CBP layer, in the electroluminescence spectrum for the OLEDs with a DEL appeared at 451 nm, which is in the deep-blue region. The Commission Internationale de l'Eclairage chromaticity coordinates of the OLEDs with a DEL at 11 V were (0.150, 0.137), indicative of a deep, stabilized blue color. These results indicate that luminance efficiency-stabilized blue OLEDs can be fabricated using a CBP/DPVBi DEL acting as electron and hole trapping layers.

Atomic force microscopy images showed that the size of the CdTe quantum dots (QDs) slightly increased with increasing annealing temperature up to 350 °C. Photoluminescence spectra showed that the excitonic peak corresponding to the interband transition from the ground electronic subband to the ground heavy-hole band (E1–HH1) in the CdTe/ZnTe QDs annealed at 350 °C was shifted to lower energy compared with that in as-grown CdTe/ZnTe QDs. The full width at half-maximum of the E1–HH1 transition peak in the CdTe/ZnTe QDs annealed at 350 °C decreased resulting from the improvement of the crystallinity for the annealed CdTe QDs.

The electrical and the optical properties of organic light-emitting devices (OLEDs), with and without multiple heterostructures consisting of N, N-bis-(1-naphthyl)-N, N-diphenyl-1,1-biphenyl-4,4-diamine (NPB)/5,6,11,12-tetraphenylnaphthacene (rubrene) acting as a hole transport layer (HTL), were investigated. The OLEDs with 3 periods of NPB/mixed rubrene:NPB multiple heterostructures acting as an HTL showed the highest luminances and efficiencies. While the electroluminescence (EL) peak corresponding to the rubrene layer did not appear for the OLEDs with 3 periods of NPB/mixed rubrene:NPB multiple heterostructures, only the EL peak related to the tris (8-hydroxyquinoline) aluminum layer was observed. The Commission Internationale de l’Eclairage chromaticity coordinates of the OLEDs with 3 periods of NPB/mixed rubrene:NPB multiple heterostructures at 14 V were (0.321, 0.531), indicative of a deep stabilized green color.

The degradation behaviors of the electrical and the optical properties of organic light-emitting devices (OLEDs) fabricated with an emitting layer (EML) doped with or without a wide-bandgap-impurity were investigated. The OLEDs with a wide-bandgap-doped Alq 3 EML were more stable than those with an undoped Alq 3 EML. The existence of the doped wide-bandgap-impurity in the EML decreased the trap-charge density in the EML, resulting in an increase in the number of electrons in the Alq 3 EML. That increases in the number of electron in the Alq 3 EML for the OLEDs with a wide-bandgap-impurity decreased the staying time of the holes in the Alq 3 EML, resulting in an enhanced lifetime for the OLEDs. These results indicate that OLEDs with a wide-bandgap-impurity-doped EML hold promise for potential applications in long-lifetime OLED displays.

The light extraction efficiencies of organic light emitting diodes (OLEDs) utilizing various kinds of porous alumina films with different pore diameters were investigated. The OLEDs with the porous alumina film deposited on the glass surface were fabricated to improve their light extraction efficiency. The porous alumina film was fabricated by using a two step anodizing electrochemical procedure. The current densities as functions of the applied voltage do not significantly change, regardless of the existence and the magnitude of the pore diameter in the porous alumina film. The luminance efficiency of the OLEDs increased with increasing pore diameter. The luminance efficiency of the OLEDs utilizing the porous alumina film with a pore diameter of 70 nm was enhanced approximately 9% in comparison with that of the OLEDs without the porous alumina film. These results indicate that highly efficient OLEDs can be fabricated using a porous alumina film with an optimum pore diameter.

The photo and cathodoluminescence of zinc oxide (ZnO) filled opal arrays, as well as ZnO nanocrystals prepared by a chemical deposition method were investigated. The photoluminescence (PL) from the arrays was studied using angular resolution. The PL spectra of the filled opal exhibited a dip corresponding to the array’s photonic band gap. ZnO nanocrystals embedded in the opal matrix demonstrated quenched excitonic emission while the opal matrix showed enhanced emission. This effect is explained by an energy transfer from ZnO nanocrystals to the opal matrix.

The equivalent circuit models in organic light-emitting diodes (OLEDs) consisting of indium-tin-oxide (ITO)/tris(8-hydroxyquinoline) Aluminum (Alq3)/Aluminum (Al), ITO/Alq3/Lithium quinolate/Al or ITO/N,N-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB)/Alq3/Al were investigated. The relaxation times were obtained from the impedances as functions of frequencies, and the equivalent circuits in the OLEDs were designed by using the relaxation times of OLEDs determined from the impedance spectroscopies. The Cole-Cole plots calculated from the equivalent circuit models were in reasonable agreements with the experimental results. These results can help designing equivalent circuit models of multilayer OLEDs.

CdTe thin films were grown on GaAs (1 0 0) substrates by using molecular beam epitaxy at various temperatures. The bright-field transmission electron microscopy (TEM) images and the high-resolution TEM (HRTEM) images showed that the crystallinity of CdTe epilayers grown on GaAs substrates was improved by increasing the substrate temperature. The result of selected-area electron diffraction pattern (SADP) showed that the orientation of the grown CdTe thin films was the (1 0 0) orientation. The lattice constant the strain, and the stress of the CdTe thin film grown on the GaAs substrate were determined from the SADP result. Based on the SADP and HRTEM results, a possible atomic arrangement for the CdTe/GaAs heterostructure is presented.

CdTe thin films were grown on GaAs (100) substrates by using molecular beam epitaxy at various temperatures. The results of the X-ray diffraction (XRD) patterns showed that the orientation of the grown CdTe thin films was the (100) orientation. XRD patterns, atomic force microscopy images, high-resolution transmission electron microscopy (HRTEM) images, and photoluminescence spectra showed that the crystallinity of CdTe (100) epilayers grown on GaAs (100) substrates was improved by increasing the substrate temperature. HRTEM images showed that misfit dislocations existed at the CdTe / GaAs heterointerface. These results can help improve understanding of the substrate temperature effect on the structural and the optical properties of CdTe (100)/ GaAs (100) heterostructures.

The electrical and the optical properties of organic light-emitting diodes (OLEDs) fabricated utilizing nickel-oxide (NiO) buffer layers between the anodes and the hole transport layers were investigated. The NiO layer was formed by using a thermally evaporated nickel thin film and a subsequent oxidation process. The tunneling holes in the OLED were increased due to the existence of the NiO layer between the anode and the hole transport layer, resulting in enhanced efficiency for the OLED. These results indicate that OLEDs with NiO buffer layers hold promise for potential applications in highly-efficient flat-panel displays.

Scanning electron microscopy (SEM), Fourier transform infrared (FTIR) transmission, and Hall effect measurements were performed to investigate the structural, optical, and electrical properties of as-grown and in situ-annealed Hg0.7Cd0.3Te epilayers grown on CdTe buffer layers by using molecular beam epitaxy. After the Hg0.7Cd0.3Te epilayers had been annealed in a Hg-cell flux atmosphere, the SEM images showed that the surface morphologies of the Hg0.7Cd0.3Te thin films were mirror-like with no indication of pinholes or defects, and the FTIR spectra showed that the transmission intensities had increased in comparison to that of the as-grown Hg0.7Cd0.3Te epilayer. Hall-effect measurements showed that n-Hg0.7Cd0.3Te epilayers were converted to p-Hg0.7Cd0.3Te epilayers. These results indicate that the surface, optical, and electrical properties of the Hg1 − xCdxTe epilayers are improved by annealing and that as-grown n-Hg1 − xCdxTe epilayers can be converted to p-Hg1 − xCdxTe epilayers by in situ annealing.

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.

The electrical and the optical properties of organic light-emitting devices (OLEDs) consisting of aluminum (Al)/lithium quinolate/tris (8-hydroxyquimoline) Al/5,6,11,12-tetraphenylnaphthacene (rubrene)-doped N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1-biphenyl-4,4′-diamine (NPB)/indium-tin-oxide/glass structures fabricated with uniformly doped and stepwise-doped hole transport layers (HTLs) were investigated. The turn-on voltage of the OLEDs fabricated utilizing a stepwise-doped HTL was smaller than that of the OLEDs fabricated with a uniformly doped HTL, and the corresponding luminance at the same voltage was higher. The Commission Internationale de l'Eclairage (CIE) chromaticity coordinates of the OLEDs fabricated utilizing a stepwise-doped HTL became stabilized, and the CIE chromaticity coordinates of the OLEDs at 12 V was (0.43, 0.53), indicative of a yellow emission corresponding to the rubrene layer. The luminescence mechanisms of the OLEDs fabricated utilizing a stepwise-doped HTL are described on the basis of the experimental results.

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 effect of thermal annealing on self-assembled uncapped InAs/GaAs quantum dots (QDs) has been investigated using transmission electron microscopy (TEM) and photoluminescence (PL) measurements. The TEM images showed that the lateral sizes and densities of the InAs QDs were not changed significantly up to 650 °C. When the InAs/GaAs QDs were annealed at 700 °C, while the lateral size of the InAs QDs increased, their density decreased. The InAs QDs disappeared at 800 °C. PL spectra showed that the peaks corresponding to the interband transitions of the InAs QDs shifted slightly toward the high-energy side, and the PL intensity decreased with increasing annealing temperature. These results indicate that the microstructural and the optical properties of self-assembled uncapped InAs/GaAs can be modified due to postgrowth thermal annealing.

Microstructural and atomic structure studies of GaN/sapphire and AlxGa1−xN∕AlN∕GaN heterointerfaces have been performed by using bright-field transmission electron microscopy (TEM) and selected area electron diffraction pattern (SADP) measurements. TEM and SADP results from the GaN/sapphire and the Al0.4Ga0.6N∕AlN∕GaN∕sapphire heterointerfaces showed that GaN epilayers and Al0.4Ga0.6N, AlN, and GaN active layers, respectively, had been grown on the sapphire substrates. The values of the strain and the stress in the Al0.4Ga0.6N, the AlN, and the GaN layers were determined. Possible schematic diagrams of the two heterostructures, as well as diagrams of the [21¯1¯0] projections of the GaN epilayer and the Al0.4Ga0.6N∕AlN∕GaN heterostructure, are presented based on the TEM and SADP results. These results can help improve the understanding of the microstructural properties of the strained AlxGa1−xN∕AlN∕GaN∕sapphire heterostructures for applications in the high-speed and high-power electronic devices.

An alternative method for modulation of light generated by AlGaN/InGaN multiple quantum well laser with quartz antireflective (AR) coatings covering the resonator windows was modelled and studied theoretically. Disturbance of the piezoelectric coatings caused by surface acoustic waves (SAW) results in efficient intensity modulation of the laser beam. The model for the laser diode operating at DC demonstrates that the modulation factor can exceed 0.2 in sub-nanometer SAW displacement. For quarter-wave AR films, the carrier frequency of modulated beam has twice the frequency of SAW.

CdxZn1−xTe single crystals were grown by using the Bridgman method. Hall-effect measurements showed that the carrier type and carrier concentration of unintentionally CdxZn1−xTe crystals were p type and between approximately 1014 and 1015, respectively. Phototransmission spectra showed that the position of the band edge emission shifted to higher wavelength with increasing Cd mole fraction, and photoluminescence spectra showed that the peak corresponding to the excitons bound to neutral acceptors shifted to lower energy with increasing Cd mole fraction. The electro-optic sensors fabricated utilizing the CdxZn1−xTe single crystals were operated in the terahertz spectrum range. These results can help improve the understanding of CdxZn1−xTe single crystals for applications in terahertz electro-optic sensors.

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.

Spectroscopic ellipsometry measurements on ZnO nanocrystalline textured films grown on p-InP (100) substrates by using radio-frequency magnetron sputtering at room temperature were carried out to investigate their optical parameters. Transmission electron microscopy measurements showed that ZnO thin films grown on p-InP (100) substrates were nanocrystalline. The dielectric function, the refractive indice, and the extinction coefficient of the ZnO thin films were determined as functions of the photon energy, and the energy gap of the ZnO nanocrystalline film was 3.38 eV. These results can help to improve the understanding of the ZnO nanocrystalline thin film grown on p-InP (100) substrates for potential use in optoelectronic devices based on InP substrates.

Atomic force microscopy (AFM) and photoluminescence measurements were carried out to investigate both the formation of CdTe/ZnTe nanostructures and their electron activation energies for various delay times between the deposition of the CdTe layer and the introduction of nitrogen gas into the same chamber. The AFM images show that CdTe quantum dots (QDs) are formed. While the excitonic peak associated with the transition from the ground electronic subband to the ground heavy-hole band (E1-HH1) shifted to higher energy with increasing thickness of the CdTe thin film up to delay time of 10 s, it shifted to lower energy with an increasing thickness of the CdTe thin film for delay times from 20 to 60 s. The activation energy of the electrons confined in the 3.5 ML CdTe QDs grown with a delay time of 5 s was higher than it was for the electrons in CdTe nanostructures grown with delay times of 0 and 60 s. The present results can help to improve the understanding of how the formation of and the electron activati...

High-quality Hg1−xCdxTe epilayers on CdTe buffer layers were grown by molecular beam epitaxy using various growth methods. The reflection high-energy electron diffraction, scanning electron microscopy, and atomic force microscopy measurements showed that the crystallinity and electrical properties of the Hg1−xCdxTe epilayers grown on CdTe buffer layers deposited by using a two-step annealing growth method were improved. These results indicate that high-quality Hg1−xCdxTe films can be obtained by using CdTe buffer layers grown by the two-step annealing growth method and that the grown Hg1−xCdxTe epilayers hold promise for potential applications in optoelectronic devices in the area of infrared detectors.

Photoluminescence (PL) and spectroscopic ellipsometry measurements on ZnTe/GaAs strained heterostructures grown by molecular beam epitaxy were carried out to investigate the strain effect depending on the ZnTe epitaxial layer thickness. PL spectra show that the PL peaks corresponding to the excitons bound to neutral acceptors shift toward the higher-energy side with increasing the ZnTe film thickness. As the strain increases, the value of the critical-point energy shift obtained from the spectroscopic ellipsomerty increases. The strains in the ZnTe layers grown on GaAs substrates are expected to decrease with increasing the ZnTe layer thickness. These results indicate that the strains in the ZnTe layers grown on GaAs substrates are strongly dependent on the ZnTe layer thickness.

Four-port frustrated total internal reflection couplers in InP-based GalnAsP quantum-well substrates are realized and characterized. Each coupler forms an "X" at the perpendicular intersection of two ridge waveguides and is aligned 45° to the optical path. The 180-nm-wide couplers are fabricated by dry etching deep trenches through the quantum wells and backfilling with alumina (n = 1.71) by atomic layer deposition. Coupling coefficients for the fabricated coupler are in good agreement with a three-dimensional finite-difference time-domain theory, and an 82% coupler efficiency is estimated.

We have found unusual re-evaporation effect on the surface morphology of GdxY1−xCa4O(BO3)3 (GdxY1−xCOB) films grown by combinatorial laser molecular-beam epitaxy. The surface morphologies of the GdxY1−xCOB films grown on the atomically flat (0 1 0) GdCa4O(BO3)3 (GdCOB) substrates were strongly dependent on the deposition conditions such as substrate temperature and laser repetition rate. Decreasing the substrate temperature and/or increasing the laser repetition rate improved the surface morphology of the film since at such deposition conditions, re-evaporation which may make film surface rough could be effectively restrained. GdxY1−xCOB film grown at 500 °C and 4 Hz exhibited the ultra-smooth surface like that of the atomically smooth (0 1 0) GdCOB substrate. Under such conditions, intensity monitoring of reflection high-energy electron diffraction revealed the layer-by-layer growth of the film. Using this regulated growth behavior of the films we have successfully fabricated such nano-structured films as [GdCOB/YCa4O(BO3)3] superlattices.

Lattice-mismatched ZnTe epilayers on GaAs (1 0 0) substrates with and without ZnSe buffer layers were grown by using molecular beam epitaxy. AFM, XRD, and TEM measurements were performed to investigate the surface and structural properties of the ZnTe thin films. Photoluminescence, Raman scattering, and TEM measurements showed that the crystallinity of a ZnTe epilayer grown on a GaAs substrate was remarkably improved by using a ZnSe buffer layer. Photoreflectance measurements showed that the strain of the ZnTe layer with the ZnSe buffer layer was smaller than that without the ZnSe buffer layer. These results indicate that ZnTe epitaxial films grown on GaAs substrates with ZnSe buffer layers hold promise for potential applications in optoelectronic devices operating in the blue–green spectral region.

Spectroscopic ellipsometry and photoluminescence (PL) measurements on SnO2 nanocrystalline textured films grown on p-InSb (111) substrates by using radio-frequency magnetron sputtering at low temperature were carried out to investigate the dependence of the optical parameters on the SnO2 thin film thickness. As the SnO2 film thickness increases, while the energy gap of the SnO2 film decreases, its refractive index increases. The PL spectra show that the broad peaks corresponding to the donor–acceptor pair transitions are dominant and that the peak positions change with the SnO2 film thickness. These results can help improve understanding for the application of SnO2 nanocrystalline thin films grown on p-InSb (111) substrates in potential optoelectronic devices based on InSb substrates.

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.

The microstructural and the optical properties of InAs/GaAs quantum-dot (QD) arrays inserted into undoped GaAs barriers embedded in an AlxGa1−xAs/GaAs were investigated by using transmission electron microscopy (TEM) and photoluminescence (PL) measurements. The TEM images and the selected-area electron diffraction patterns showed that vertically stacked InAs QD self-assembled arrays were embedded in the GaAs barriers. The temperature-dependent PL spectra showed that the peak corresponding to the interband transitions from the ground electronic subband to the ground heavy-hole band of the InAs QDs shifted to lower energy with increasing temperature. The PL intensity of the InAs dots was significantly enhanced by the modulation-doped AlxGa1−xAs/GaAs heterostructure, and the thermal activation energy of the InAs dots was decreased by the addition of the modulation-doped AlxGa1−xAs/GaAs heterostructure. The present results can help to improve the understanding of the microstructural and the optical properties...

Transmission electron microscopy images showed that multiply stacked CdSe quantum-dot (QD) arrays with a large ZnSe spacer thickness were embedded in the ZnSe barriers. The temperature-dependence photoluminescence (PL) spectra showed that the peak corresponding to the interband transitions from the ground electronic subband to the ground heavy-hole band of the CdSe QDs shifted to a lower energy side with increasing temperature and that the PL linewidth at high temperature increased with increasing temperature. The activation energy of the electrons confined in the CdSe QDs was as large as 100 meV. The present observation can help improve understanding of the microstructural and optical properties in multiply stacked CdSe/ZnSe QDs.

Photoluminescence (PL) measurements have been performed to investigate the compositional intermixing of In 0.53 Ga 0.47 As/InP multiple quantum wells (MQWs) grown by using chemical beam epitaxy. A SiN x capping layer together with a thermal annealing process was introduced to create the energy shift of the exciton transition from the first electronic subband to the first heavy hole (E 1 -HH 1 ) in the In 0.53 Ga 0.47 As/InP MQWs. The blue shift of the (E 1 -HH 1 ) transition is attributed to the interdiffusion of the P in the InP barrier and the As in the In 0.53 Ga 0.47 As quantum well. These results indicate that the value of the (E 1 -HH 1 ) shift can be effectively adjusted by the annealing temperature and the annealing time in the energy range of 87 meV and that the intermixing method of In 0.53 Ga 0.47 As/InP MQWs by using a SiN x capping layer together with a annealing process holds promise for practical applications in the intergrated photonic devices.

The growth of MgO thin films on p-InP (100) substrates by using electron-beam deposition at a relatively low temperature (∼200°C) was performed in order to produce high-quality MgO/p-InP (100) heterointerface and MgO insulator gates with dielectric constants of low magnitude. Atomic force microscopy and X-ray diffraction measurements showed that the MgO films grown on the InP substrates were polycrystalline thin layers with very smooth surfaces. Transmission electron microscopy and selected-area diffraction measurements showed that the grown MgO films were polycrystals with small domains and that the MgO/InP (100) heterointerface had no significant interdiffusion problem. Room-temperature current–voltage and capacitance–voltage (C–V) measurements clearly revealed a metal–insulator–semiconductor behavior for the diodes with MgO insulator gates, and the interface state densities at the MgO/p-InP interfaces, as determined from the C–V measurements, were approximately 4.5×1011 eV−1 cm−2 at an energy of about 0.7 eV below the conduction-band edge. The dielectric constant of the MgO thin films, as determined from the C–V measurements, was as low as 9.67. These results indicate that the MgO layers grown on p-InP (100) substrates at low temperature hold promise for potential electronic devices based on InP substrates.

ZnO thin films were grown on InSb (111) substrates with the goal of producing high-quality ZnO films and ZnO/InSb heterostructures. Atomic force microscopy images showed that the root-mean-square average surface roughness of the ZnO film was 17.26 A, and X-ray diffraction measurements showed that the ZnO films grown on the InSb (111) substrates were preferential orientation in the [0001] crystal direction. Auger electron spectroscopy and bright-field transmission electron microscopy measurements showed that the ZnO/InSb heterostructures had no significant intermixing problems and had relatively sharp interfaces. The temperature dependence of the photoluminescence spectra showed dominantly the bound excition peaks at low temperature and the free exciton emission band at high temperature. These results indicate that ZnO (0001) preferential orientation textural films grown on p-InSb (111) substrates at low temperature hold promise for potential high-speed optoelectronic devices based on InSb substrates.

Strain effects in highly lattice-mismatched InAs 0.6 P 0.4 /InP modulation-doped single quantum wells were investigated by the high-resolution transmission electron microscopy (HRTEM), the selected-area electron diffraction pattern (SADP), and the Raman scattering spectroscopy measurements. The HRTEM and the SADP measurements on the InAs 0.6 P 0.4 /InP single quantum wells showed that the InAs 0.6 P 0.4 active layer was grown pseudomorphologically on the InP buffer layer in spite of highly lattice mismatch. The values of the horizontal and vertical strains and the horizontal stress of the InAs 0.6 P 0.4 layer are - 1.9 × 10 -2 , 2.1 × 10 -2 , and - 16.26 × 10 -2 dyne cm −2 , respectively. A possible crystal structure for the InAs 0.6 P 0.4 /InP single quantum well is presented based in the HRTEM and the SADP results. These results can help improve understanding the microstructural properties of strained InAs x P 1-x /InP modulation-doped single quantum wells.

A new approach has been introduced for the fabrication of Ru/p-InP(100) heterostructures with the goal of producing stable Ru contacts and sharp Ru/p-InP heterointerfaces. Atomic force microscopy and X-ray diffraction measurements showed that the Ru film layers grown on InP substrates were polycrystalline thin films with very smooth surfaces. Auger electron spectroscopy and Rutherford backscattering measurements showed that the composition of the as-grown film was Ru and that the Ru/InP interface quality was relatively good. Transmission electron microscopy and selected-area electron-diffraction measurements showed that the grown Ru film was a polycrystalline layer with small grain domains. These results can help improve understanding for the application of Ru/InP heterostructures in high-speed metal–semiconductor field-effect transistors.

MgO thin films grown on p-GaAs (100) substrates by using electron-beam deposition at a relatively low temperature (∼250°C) was performed in order to produce high-quality MgO/p-GaAs (100) heterointerfaces and MgO good insulator gates. Atomic force microscopy and X-ray diffraction measurements showed that the MgO films grown on the GaAs (100) substrates were (110) oriented epitaxial layers with smooth surfaces. Transmission electron microscopy measurements showed that the MgO/GaAs (100) heterointerface had no significant interdiffusion problem. Room-temperature current-voltage and capacitance-voltage (C—V) measurements clearly revealed a metal-insulator-semiconductor behavior for the diodes with MgO insulator gates. The dielectric constant and the interface state density at the MgO/p-GaAs interface were 9.06 and 1.9 × 10 11 eV −1 cm −2 at an energy of about 0.7 eV below the conduction-band edge, respectively. These results indicate that the MgO epitaxial films grown on p-GaAs (100) substrates at low temperature hold promise for potential applications in high-frequency electronic devices.

A new approach was used for combining GaN and porous Si with the goal of producing high-quality GaN epitaxial layers for optoelectronic integrated circuit devices based on Si substrates. Reflection high-energy electron diffraction (RHEED), x-ray diffraction (XRD), photoluminescence (PL), and Van der Pauw–Hall effect measurements were performed to investigate the structural, optical, and electrical properties of the GaN epitaxial films grown on porous Si(100) by plasma-assisted molecular-beam epitaxy with a two-step method. The RHEED patterns were streaky with clear Kikuchi lines, which was direct evidence for layer-by-layer two-dimensional growth of GaN epitaxial layers on porous Si layers. The XRD curves showed that the grown layers were GaN(0001) epitaxial films. The results of the XRD and the PL measurements showed that the crystallinities of the GaN epilayers grown on porous Si by using a two-step growth were remarkably improved because the porous Si layer reduced the strains in the GaN epilayers by sharing them with the Si substrates. Hall-effect measurements showed that the mobility of the GaN active layer was higher than that of the GaN initial layer. These results indicate that high-quality GaN epitaxial films grown on porous Si(100) by using two-step growth hold promise for potential applications in new kinds of optoelectronic monolithic and ultralarge integrated circuits.

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.