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Atomic force microscopy (AFM) measurements were carried out to investigate the structural properties of CdTe/ZnTe quantum rings (QRs), and photoluminescence (PL) measurements were performed to determine the electron activation energy. The AFM images showed that uniform CdTe QRs were formed on ZnTe buffer layers. While the excitonic peak corresponding to the transition from the ground electronic subband to the ground heavy-hole band (E1–HH1) in the CdTe/ZnTe QRs was shifted to higher energy in comparison with that in CdTe/ZnTe quantum wires and quantum wells, it was shifted to lower energy in comparison with that in CdTe/ZnTe quantum dots. The activation energy of the electrons confined in the CdTe QRs, as obtained from the temperature-dependent PL spectra, was higher than those in CdTe quantum wires and quantum wells and smaller than that in CdTe quantum dots. The present results can help improve understanding of the formation and optical properties of the CdTe QRs grown on ZnTe buffer layers.

Atomic force microscopy (AFM) and photoluminescence (PL) measurements were carried out to investigate the structure and to determine the electron activation energy in CdTe/ZnTe pyramids grown by using molecular beam epitaxy and atomic layer epitaxy methods. The AFM images showed that self-assembled CdTe pyramids were formed on ZnTe buffer layers. The PL spectra showed that the formed CdTe pyramids had quantum states and that the excitonic peak corresponding to the transition from the ground electronic subband to the ground heavy-hole band (E1–HH1) in the CdTe/ZnTe pyramids was shifted to higher energy in comparison with that in CdTe/ZnTe quantum dots (QDs). The activation energy of the electrons confined in the CdTe pyramids, as obtained from the temperature-dependent PL spectra, was higher than that in CdTe QDs. These results can help improve an understanding of the formation and optical properties in self-assembled CdTe pyramids with quantum states.

Self-assembled CdTe quantum wires (QWRs) were grown on ZnTe buffer layers by using molecular-beam epitaxy. Atomic force microscopy images showed that preferentially oriented CdTe QWRs were formed on ZnTe buffer layers. The activation energy of the electrons confined in the CdTe QWRs, as obtained from the temperature-dependent photoluminescence spectra, was higher than that of electrons in CdTe/ZnTe quantum wells. These results indicate that self-assembled CdTe QWRs grown on ZnTe buffer layers hold promise for potential applications in optoelectric devices operating in the blue–green region of the spectrum.

Hall-effect, Fourier transform infrared (FTIR) transmission, and photopresponse measurements were performed to investigate the optical and electrical properties of as-grown and in situ-annealed Hg0.7Cd0.3Te epilayers grown on CdTe buffers on GaAs (211) B substrates layers by using molecular-beam epitaxy. Hall-effect measurements showed that as-grown n-Hg0.7Cd0.3Te epilayers were converted to p-Hg0.7Cd0.3Te epilayers due to in situ annealing. The carrier concentration and the mobility as functions of the annealing temperature were determined from the Hall-effect measurements. The FTIR spectra showed that the transmission intensity 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. The activation energy and the carrier lifetime of the annealed Hg0.7Cd0.3Te epilayer were 0.25 eV and 160 ns, respectively. These results indicate that p-type Hg0.7Cd0.3Te epilayers grown on CdTe buffe...

The strain effects in and the crystal structures of self-assembled InAs/GaAs quantum dots (QDs) were investigated by using transmission electron microscopy (TEM). The in-plane lattice constant of the InAs QDs was larger than that of the GaAs substrate, and the vertical lattice constant of the InAs QDs was smaller than that of the InAs bulk. The variation of the lattice constant for the InAs QD originated from the strain effect. A schematic diagram of a strained InAs QD based on the TEM results, indicative of the strain distribution around the QD, is presented.

Temperature-dependent photoluminescence measurements showed that the activation energy of CdTe/ZnTe quantum dots (QDs) coupled with a quantum well is much larger than that of the QDs alone, This behavior is attributed to the tunneling of carriers via a thin separation layer from the quantum well to the QDs. The present observations can help improve understanding of the enhancement of the activation energy in coupled CdTe/ZnTe nanostructures.

Photoluminescence spectra showed that the formation mechanism for CdTe layers grown on ZnTe thin films changed from a two-dimensional mode to a three-dimensional mode with increasing submonolayer CdTe layer thickness, and the temperature-dependent PL spectra indicated that the activation energy of CdTe quantum dots is larger than that of CdTe single quantum wells. The formation mechanism for the CdTe QDs is in reasonable agreement with a Stranski–Krastanov growth mode.

Atomic force microscopy (AFM) and photoluminescence (PL) measurements were carried out to investigate the coalescence and electron activation energy in CdTe/ZnTe nanostructures. The results of the AFM images show that uniform CdTe quantum dots (QDs) are formed and that the transformation from CdTe QDs to CdTe quantum wires is caused by the coalescence. The excitonic peaks corresponding to the transition from the ground electronic subband to the ground heavy-hole band in the CdTe/ZnTe QDs shifted to higher energy in comparison with those of the CdTe/ZnTe quantum wires. The activation energy of the electrons confined in the CdTe QDs, as obtained from the temperature-dependent PL spectra, was higher than those in CdTe quantum wells and quantum wires. The present results can help to improve the understanding of coalescence and electron activation energy in CdTe/ZnTe nanostructures.

A focused-ion-beam (FIB) technique utilizing both lithographic and nanoparticle formation processes has been introduced to fabricate a single-electron transistor (SET) that can operate at room temperature. The results for the drain current as a function of the gate voltage at different source voltages at room temperature clearly show Coulomb oscillations indicative of Coulomb-blockade effects. These results indicate that SETs operating at room temperature, fabricated utilizing the FIB technique, hold promise for potential applications in ultra-high-density memory devices.

Bright-field transmission electron microscopy (TEM) and high-resolution TEM images and an electron diffraction pattern showed that the SnO2 layers grown on heavily doped n-InP(100) substrates were nanoscale thin films. X-ray photoelectron spectroscopy showed that the positions of the peaks corresponding to the Sn 3d5/2, the Sn 3d3/2, and the O 1s levels for the SnO2 thin film were slightly shifted toward the lower energy side in comparison with those for bulk SnO2. The refractive indices obtained by spectroscopic ellipsometry were above 2.2 around the SnO2 energy gap of the SnO2 thin films. The maximum intensity of the optical transmittance for the SnO2 nanoscale thin film with 3939 A thickness was above 90%.

We studied the atomic-scale growth control and second-harmonic generation (SHG) properties of GdxY1−xCa4O(BO3)3 thin films. Combinatorial laser molecular-beam epitaxy was employed to optimize the growth conditions of the film. Ultrasmooth GdxY1−xCa4O(BO3)3 thin films with step-and-terrace structure were obtained by using atomically controlled GdCa4O(BO3)3 substrates. The dependence of SHG intensity on the fundamental wave polarization angle was studied for the epitaxial film on (010) GdCa4O(BO3)3 substrate in comparison for the randomly oriented film on (0001) sapphire substrate. It was found that only the epitaxially grown film clearly exhibited a fourfold SHG intensity showing type-II phase-matching direction.

The transmission electron microscopy image and selected area electron diffraction pattern showed that self-assembled InAs quantum-dot (QD) arrays embedded in GaAs barriers were periodically inserted in an Al0.25Ga0.75As/GaAs heterostructure. The temperature-dependent photoluminescence spectra of the InAs/GaAs quantum dots embedded in modulation-doped heterostructures showed interband transitions from the first-excited electronic subband to the first-excited heavy-hole subband together with those from the ground subband to the ground heavy-hole band (E1–HH1) while the spectra of the InAs/GaAs QDs alone showed only the peak related to the (E1–HH1) transitions.

Selected area electron diffraction pattern (SADP) and transmission electron microscopy (TEM) measurements were carried out to investigate the ordered structure in CdxZn1−xTe epitaxial layers grown on (001) GaAs substrates. The SADP showed to sets of superstructure reflections with symmetrical intensities, and the corresponding high-resolution TEM image showed a doublet periodicity in the contrast of the {111} lattice planes. The results of the SADP and the TEM measurements showed the existence of a CuPt-type ordered structured in the CdxZn1−xTe epitaxial layers. This CuPt-type ordered structure had two different variants with an antiphase boundary existing between the two variants. The formation of a CuPt-type ordered structure in a CdxZn1−xTe epitaxial layer might originate from the minimization of the strain relaxation energy in the reconstructed GaAs (001) surface. A possible atomic arrangement of and a formation mechanism for the CuPt-type ordered structure in the CdxZn1−xTe epitaxial layer are presen...

Top-emitting arrays of organic light-emitting diodes (OLEDs) have been fabricated and demonstrated on complementary metal–oxide–silicon (CMOS) circuitry. The 8×8 array of OLEDs is composed of 90 μm micropixels with a 55 μm separation. The OLEDs are based on an emitting layer of tris-(8-hydroxyquinoline)aluminum (Alq3) doped with coumarin 6 to provide green light emission. A layer of N,N′-diphenyl-N, N′-bis(3-methylphenyl)1-1′-biphenyl 1-4, 4′-diamine (TPD) was used as a hole transport layer and poly(ethylenedioxythiophene) doped with polystyrenesulfonate was used as a buffer layer between the TPD and the CMOS anode metal. Bright light was emitted through a semitransparent Mg:Ag cathode when the micropixel was driven by an individual current source.

Al two-terminal diodes were fabricated on a basis of an artificial pattern formation method using focused ion-beam (FIB) techniques. The results of current–voltage and conductance–voltage measurements at room temperature showed the Coulomb staircase and the Coulomb blockade effects, respectively. The Coulomb blockade effects originate from the many nanoparticles created by the defects due to the Ga+ ion beam. These results indicate that Al two-terminal diodes fabricated by using the FIB system hold promise for potential applications in single-electron transistors operating at room temperature.

Photoluminescence (PL) measurements were carried out to investigate the interband transitions in CdxZn1−xTe/ZnTe asymmetric step quantum wells with and without an applied electric field. Transmission electron microscopy showed that the CdxZn1−xTe/ZnTe step quantum wells consisted of a shallow Cd0.1Zn0.9Te well and a deep Cd0.18Zn0.82Te well bound by two thick ZnTe barriers. The results for the PL data at 300 K for several applied electric fields showed that the excitonic transition from the first electronic state to the first heavy-hole state shifted to the larger energy side as the applied electric field increased. The electronic subband energies and the wave functions in the step quantum wells were calculated by an envelope-function approximation method, taking into account the strain effects, and the calculated values of the interband transitions were in qualitative agreement with those obtained from the PL measurements. The Stark shift of the step quantum well was much more sensitive to the applied el...

Metalorganic chemical vapor deposition of BaTiO3 using Ba(tmhd)2, Ti(OC3H7)4, and N2O via pyrolysis at relatively low temperature (∼300 °C) was performed in order to produce high‐quality BaTiO3/p‐InP (100) interfaces and BaTiO3 insulator gates with dielectric constants of high magnitude. Scanning electron microscopy showed that the surfaces of the BaTiO3 films had very smooth morphologies. Auger electron spectroscopy measurements showed that the compositions of the as‐grown films consisted of barium, titanium, and oxygen. Transmission electron microscopy showed that the BaTiO3 films had interdiffusion and local epitaxial formations near the BaTiO3/p‐InP (100) interfaces. Room‐temperature current‐voltage and capacitance‐voltage (C‐V) measurements clearly revealed metal‐insulator‐semiconductor behavior for the BaTiO3 insulator gates, and the interface state densities at the BaTiO3/p‐InP interfaces were approximately low 1011 eV−1 cm−2 at an energy about 0.6 eV below the conduction‐band edge. The dielectric ...

Metalorganic chemical vapor deposition of titanium dioxide (TiO2) on p‐Si(100) using titanium isopropoxide and nitrous oxide via pyrolysis at relatively low (∼500 °C) temperature was performed to produce high quality TiO2/p‐Si interfaces and to fabricate TiO2 insulator gates with a dielectric constant of high magnitude. Scanning electron microscopy shows that the surfaces of the TiO2 films have very smooth morphologies. From the x‐ray diffraction analysis, the grown layer was found to be a polycrystalline film. Raman spectroscopy showed the optical phonon modes of a TiO2 thin film. The stoichiometry of the TiO2 film was investigated by Auger electron spectroscopy. Room‐temperature current‐voltage and capacitance‐voltage measurements clearly revealed metal‐insulator‐semiconductor behavior for the samples of the Ag/TiO2/p‐Si. The interface state density at the TiO2/p‐Si interface was approximately high 1011 eV−1 cm−2 at the middle of the Si energy gap, and the dielectric constant determined from the capacitance‐voltage measurements was as large as 73. These results indicate the TiO2 layers grown at relatively low temperature can be used for high density dynamic memory.

Metalorganic chemical vapor deposition of PbTiO3 using Pb (tmhd)2, Ti(OC3H7)4, and N2O via thermal pyrolysis at relatively low temperature (∼500 °C) was performed in order to produce PbTiO3 insulator gates with high quality PbTiO3/p‐Si interfaces. Raman spectroscopy showed the several optical phonon modes of the PbTiO3/p‐Si structure. The stoichiometry of the PbTiO3 films was observed by Auger electron spectroscopy. Room‐temperature current‐voltage and capacitance‐voltage measurements clearly revealed metal‐insulator‐semiconductor behavior for the samples with a PbTiO3 insulator gate, and the interface state densities at the PbTiO3/p‐Si were approximately 1011 eV−1 cm−2 at the middle of the Si energy gap.

Millimeter mixers have been fabricated from epitaxial films of Tl2CaBa2Cu2O8, using a bowtie antenna structure integrated with grain‐boundary weak links that were deliberately formed during film growth. The bowtie antenna was utilized for broadband millimeter wave coupling of the radiation into the weak links. Heterodyne mixing of signals at both V band (55 GHz) and W band (94 GHz) frequencies, and subharmonic mixing at V has been observed at liquid nitrogen temperature for zero and finite bias voltage conditions. The dependence of the IF output on temperature, bias voltage, and millimeter wave signal power has been studied. Efficient mixing with bias voltage exhibited strong signals right up to Tc (101 K).

Transmission electron microscopy (TEM), high-resolution TEM, and x-ray energy dispersive spectroscopy results showed that Zn metallic nanocrystals and ZnSiO3 insulating nanocrytals embedded in a SiO2 matrix were created from the ZnO thin films deposited on n-Si (001) substrates due to rapid thermal annealing. The formed Zn metallic nanocrystals were transformed into monoclinic ZnSiO3 insulating nanocrystals with increasing number of Zn atoms resulting from an increase in the annealing time up to 10 min. The transformation mechanisms from metallic Zn nanocrystals to insulating ZnSiO3 nanocrystals in a SiO2 matrix due to rapid thermal annealing are described on the basis of the experimental results.

Transmission electron microscopy (TEM), high-resolution TEM, and atomic force microscopy images showed that the columnar structure and the surface morphology of grains in ZnO thin films grown on p-InP substrates were changed due to thermal treatment. The surface morphology variation of the ZnO thin films was attributed to the curvature modification of the subpopulations consisting of ZnO grains. While the top surface of the ZnO grains became parallel with the {0001} planes due to thermal treatment, the curvature of the subpopulations in the ZnO grains became rough. Evolution mechanisms of the surface morphology of ZnO thin films are described.

Photoluminescence spectra showed that 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 quantum dots (QDs) was shifted to a higher energy with increasing thickness of the ZnTe cap layer. The intensity of the excitonic peak related to the E1-HH1 transition for the CdTe∕ZnTe QDs increased with increasing thickness of the ZnTe cap layer. The activation energy of the electrons confined in the CdTe∕ZnTe QDs increased with increasing thickness of the ZnTe cap layer.

High electron mobility transistors (HEMTs) with InAs∕InGaAs composite channel were fabricated by employing low damage, highly selective Ne-based atomic layer etching (ALET) for the dry gate recess process. Ne-based ALET exhibited very high etch selectivity of InP over InAlAs which is suitable for dry gate recess process removing InP etch stop layer on top of InAlAs Schottky barrier layer. The plasma induced damage on the exposed InAlAs surface due to the ALET was much lower than that due to the conventional Ar-based reactive ion etching (RIE), which was verified by atomic force microscopy and Hall measurements. For further comparison, dc characteristics were compared for the two types of 0.3μm HEMTs fabricated by utilizing ALET and conventional RIE during the dry gate recess processes.

The atomic force microscopy images showed that the dimensional structural transformation from CdxZn1−xTe quantum dots (QDs) with Cd mole fractions of 0.5 and 0.6 to CdxZn1−xTe quantum wires occurred at a Cd mole fraction of 0.8. Photoluminescence spectra showed that the excitonic peak corresponding to the transition from the ground electronic subband to the ground heavy-hole band in CdxZn1−xTe∕ZnTe nanostructures shifted to a lower energy with increasing Cd mole fraction. The activation energy of the electrons confined in the CdxZn1−xTe∕ZnTe QDs with a Cd mole fraction of 0.6 was higher than those of electrons in CdxZn1−xTe∕ZnTe nanostructures.

ZnO thin films were grown on n-Si (001) substrates by using plasma-assisted molecular beam epitaxy. A cross-sectional bright-field transmission electron microscopy (TEM) image showed that small ZnO columnar grains were embedded into large columnar grains, and a selected-area electron diffraction pattern, and an x-ray diffraction pattern showed that the ZnO thin film were nearly c-axis oriented. The evolution of the ZnO columnar structure was analyzed by using the evolution of the strain due to the interaction of the columnar grains, as observed by using high-resolution TEM. The initial formation mechanisms of the supersaturation region and the columnar grains are described.

Temperature-dependent photoluminescence (PL) measurements were performed to investigate the optical properties of CdTe∕ZnTe nanostructures. The activation energy of the CdTe∕ZnTe quantum dots (QDs) sandwiched between two quantum wells (QWs) with ZnTe separation barriers, as obtained from the temperature-dependent PL spectra, was much larger than the activation energies of the QDs alone and of the QDs combined with a single QW. This behavior can be attributed to a transfer of carriers from the QWs to the QDs through a separation layer due to a nonresonant multiphonon-assisted tunneling process resulting from carrier thermal emission.

The correlation between the atomic structures and the misorientation angles of [0001]-tilt grain boundaries at triple junctions in ZnO thin films grown on Si substrates was investigated by using high-resolution transmission electron microscopy (HRTEM) measurements. The HRTEM images showed three symmetric grain boundaries and one asymmetric grain boundary around the triple junction in the ZnO film. The correlation between the atomic structures and the misorientation angles of the grain boundaries at triple junctions in ZnO films is described on the basis of the HRTEM results.

We have studied the growth of self-assembled CdTe∕ZnTe quantum dots (QDs) on both GaAs (100) and Si (100) substrates. The growth of self-assembled CdTe∕ZnTe QDs on substrates shows many difficulties which are not completely solved yet. In contrast, on GaAs substrates, good crystalline quality is obtained. The results of the atomic force microscopy images showed that CdTe∕ZnTe QDs were formed on GaAs (100) and Si (100) substrates. The activation energy of the electrons confined in the CdTe∕ZnTe QDs grown on GaAs (100) and Si (100) substrates was obtained from the temperature-dependent photoluminescence spectra.

The memory effects of ZnO nanoparticles embedded in a polyimide (PI) matrix were investigated. Transmission electron microscopy images and selected area electron diffraction patterns showed that ZnO nanocrystals were created inside the PI layer. Capacitance-voltage (C-V) measurements on Al/PI/nanocrystalline ZnO∕PI∕p-Si structures at 300K showed a metal-insulator-semiconductor behavior with a flatband voltage shift due to the existence of the ZnO nanocrystals, indicative of trapping, storing, and emission in the electrons in the ZnO nanocrystals. Possible electronic structures corresponding to the writing and erasing operations for the Al/PI/nanocrystalline ZnO∕PI∕p-Si device are described on the basis of the C-V results.

We report a high power fundamental transverse mode operation of an optically pumped 1060nm vertical-external-cavity surface-emitting laser. A diamond heat spreader was capillary bonded to the semiconductor surface. A 10W continuous wave operation with optical-to-optical conversion efficiency of 44% was achieved at room temperature. The thermal rollover was not found up to a heat sink temperature of 60°C. High efficiency and good thermal stability were mainly due to the optimization of epitaxial quality and the high conductivity of the diamond heat spreader. We have found that the increase of the round trip loss caused by the heat spreader was about 1%.

Atomic force microscopy (AFM) and photoluminescence (PL) measurements were carried out to investigate the formation process and the activation energy of different-dimensional CdxZn1−xTe∕ZnTe nanostructures. The results of the AFM images show that CdxZn1−xTe quantum dots (QDs) are formed and that the dimensional transformation from CdxZn1−xTe QDs to CdxZn1−xTe quantum wires is caused by coalescence. The excitonic peak corresponding to the transition from the ground electronic subband to the ground heavy-hole transitions in CdxZn1−xTe∕ZnTe nanostructures shifts to lower energy with increasing thickness of the CdxZn1−xTe layer due to variations in the thickness and the dimension of the layer. The activation energy of the electrons confined in the CdxZn1−xTe∕ZnTe nanostructures, as obtained from the temperature-dependent PL spectra, was significantly affected by the thickness and the dimension of the CdxZn1−xTe layer.

Selected-area electron-diffraction pattern (SADP) and high-resolution transmission electron microscopy (HRTEM) measurements were carried out to investigate the existence and the atomic arrangement of microtwins in hexagonal MnAs ferromagnetic epilayers grown on GaAs (100) substrates with monolayer InAs buffer layers 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 325 K. The SADP and HRTEM results showed that an epitaxial relationship was formed among the hexagonal MnAs layer, the InAs layer, and the zincblende GaAs substrate. Microtwins existed between the MnAs grain boundaries on top of the InAs layers. Based on the SADP and HRTEM results, we present a possible atomic arrangement of the microtwins for the MnAs-InAs-GaAs heterostructure.