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AlON phosphors with different Eu2+ doping concentrations were synthesized by solid-state reaction method. Two Eu2+ doping sites were confirmed by temperature-dependent emission intensity, band shift and biexponential decay studies. High internal quantum efficiency and tunable chromaticity coordinates make AlON:Eu2+ phosphor a suitable candidate for white light-emitting diodes application. [ABSTRACT FROM AUTHOR]

A simple critical thickness for generating lattice misfits is insufficient to describe the onset strain relaxation in InAs quantum dots (QDs). A predominant dot family is shown to relieve its strain by In/Ga interdiffusion, rather than by lattice misfits, at the onset of strain relaxation. This argument is based on photoluminescence spectra, which show the emergence of a fine blueshifted transition at the onset of strain relaxation, along with a low-energy transition from a dot family degraded by lattice misfits. From the analysis of the temperature-dependent blueshift and energy separation between the ground and excited-state transitions, the blueshift is attributed to In/Ga interdiffusion. Transmission electron microscopy suggests a relaxation-induced indium migration from the interdiffused dot family to the dislocated dot family. Post-growth thermal annealing can further relieve strain by inducing more In/Ga interdiffusion in the interdiffused dot family and more dislocations in the dislocated dot family. This study explains the co-existence of strong carrier confinement in the QDs and enormous misfit-related traps in the capacitance-voltage spectra, and an elongated QD electron-emission time. [ABSTRACT FROM AUTHOR]

The use of a differential capacitance technique for analyzing the effect of strain relaxation on the electronic energy band structure in relaxed InAs self-assembled quantum dots (QDs) is presented. Strain relaxation is shown to induce a deep defect state and compensate the ionized impurity in the bottom GaAs layer, leading to a double depletion width and a long emission time. An expression of capacitance at different frequency and voltage is derived for analyzing the experimental data. It has been shown that the relationship between the low-frequency and high-frequency capacitances can be well explained by a Schottky depletion model with a compensated concentration in the bottom GaAs layer. A simple expression is presented to account for the modulation of the free electrons in the top GaAs layer. This capacitance analysis shows a long low-energy tail for the electron ground state, suggesting not very uniform strain relaxation. The results of this study illustrate a carrier compensation effect of the defect state on the electronic energy band structure near the QDs. [ABSTRACT FROM AUTHOR]

This work presents a model for describing the shape of the spontaneous emission spectrum from a quantum-well structure. A function is introduced to specify the probability distribution for the effective band gap. Based on this model, the coexisting carrier thermal broadening and effective band gap broadening in the spontaneous emission spectrum can be separated from each other. Applying this model to the spectra of AlGaInP light-emitting diodes reveals that the probability distribution functions are almost Gaussian. Therefore, the emission spectra can be described by an analytical expression with fitted parameters. Possible reasons for this band gap broadening are discussed. The determination of the junction temperatures from the emission spectra and possible deviations of the results thus determined are also elaborated. [ABSTRACT FROM AUTHOR]

We have investigated the effect of postgrowth thermal annealing on the electron emission from InAs quantum dots (QDs) containing a misfit-related defect state induced by strain relaxation. Additional carrier depletion in the GaAs bottom layer near the QD, caused by the defect state, can effectively suppress electron tunneling from the QD, leading to the observation of a thermal emission from the QD electron ground state to the GaAs conduction band with a large emission energy of 213 meV, in contrast to defect-free nonrelaxed QDs in which an emission of 58 meV from the QD electron ground state to first excited state is observed. The emission energy is reduced to 193 meV and to 164 meV after annealing at 650 and 700 °C for 1 min, respectively. This emission energy reduction is correlated with the photoluminescence blueshift which is attributed to the interdiffusion of atoms across the QD interface. The electron emission from the QD first excited and ground states is found to be a thermal emission at high temperatures and a tunneling emission at low temperatures. The tunneling energy barrier is found to be comparable to the thermal emission energy, supporting a thermal emission to the GaAs conduction band. This study illustrates a significant effect of a defect state on the electron-emission process in the QDs, suggesting the possibility of modifying the electron emission time of the QDs by purposely introducing a deep defect state. [ABSTRACT FROM AUTHOR]

The effect of a high N incorporation in self-assembled InAs quantum dots (QDs) is investigated by analyzing the electronic and structural properties around QD region. Capacitance-voltage profiling and admittance spectroscopy shows that N incorporation into the InAs QD layer leads to drastic carrier depletion in the QD layer and neighboring GaAs layers due to the formation of a deep defect state at 0.34–0.41 eV. The signature of this defect state is similar to those defects observed in strain relaxed QDs or InGaAs/GaAs quantum wells when the InAs deposition thickness exceeds a critical thickness. Accordingly, the N incorporation might result in strain relaxation either by increasing localized strain or by inducing composition inhomogeneities, which provide nucleation sources for strain relaxation. The argument of strain relaxation is supported by transmission electron microscopy that reveals lattice misfits at the QD layer and neighboring GaAs layers. [ABSTRACT FROM AUTHOR]

This work investigates the surfactant effect on exposed and buried InAs quantum dots (QDs) by incorporating Sb into the QD layers with various Sb beam equivalent pressures (BEPs). Secondary ion mass spectroscopy shows the presence of Sb in the exposed and buried QD layers with the Sb intensity in the exposed layer substantially exceeding that in the buried layer. Incorporating Sb can reduce the density of the exposed QDs by more than two orders of magnitude. However, a high Sb BEP yields a surface morphology with a regular periodic structure of ellipsoid terraces. A good room-temperature photoluminescence (PL) at ∼1600 nm from the exposed QDs is observed, suggesting that the Sb incorporation probably improves the emission efficiency by reducing the surface recombination velocity at the surface of the exposed QDs. Increasing Sb BEP causes a blueshift of the emission from the exposed QDs due to a reduction in the dot height as suggested by atomic force microscopy. Increasing Sb BEP can also blueshift the ∼1300 nm emission from the buried QDs by decreasing the dot height. However, a high Sb BEP yields a quantum well-like PL feature formed by the clustering of the buried QDs into an undulated planar layer. These results indicate a marked Sb surfactant effect that can be used to control the density, shape, and luminescence of the exposed and buried QDs. [ABSTRACT FROM AUTHOR]

The electron-emission properties of relaxation-induced traps in InAs/GaAs quantum dots (QDs) are studied in detail using capacitance-voltage (C-V) profiling and bias-dependent deep-level transient spectroscopy. Strain relaxation is shown to induce a threading-dislocation-related trap in the top GaAs layer and a misfit-dislocation-related trap near the QD. The threading trap decreases its electron-emission energy from 0.63 to 0.36 eV from sample surface toward the QD, whereas the misfit trap gradually increases its electron-emission energy from 0.28 to 0.42 eV from near the QD toward the GaAs bottom layer, indicating that both traps near the QD have lower electron-emission energies. Hence, the emission-energy change is attributed to the related traps across the QD interface where a band offset exists. The C-V profiling at 300 K shows extended carrier depletion near the QD. As temperature is increased, an electron-emission peak emerges at the QD followed by a prominent peak, suggesting that the trap responsible for the prominent peak lies in energy below the QD electron ground state. From a simulation, this trap is identified to be the misfit trap located at the QD and at the observed emission energy below the GaAs conduction band. Based on the energy location of this trap, we deduce a possible mode of strain relaxation. [ABSTRACT FROM AUTHOR]

This work presents the deep-level photoluminescence of coherently strained GaAsN/GaAs quantum-well (QW) structures with various GaAsN thicknesses and N contents. A broad deep-level emission at ∼1.1 eV is observed, whose wavelength is redshifted as the GaAsN thickness increases. Based on its energy separation from the QW emission, this emission is attributed to a transition between the QW electron ground state and a deep level at ∼0.2 eV above the GaAsN valence-band (VB) edge. This level is shown to be tied to the GaAs band edge. A transition between this level and the GaAs conduction band allows the GaAsN–GaAs band alignment to be evaluated. A type II band lineup is obtained with VB offsets of 0.03 and 0.002 eV for N=0.6% and 1.8%, respectively. The decreased VB offset suggests a transition from type II to type I with increasing N content. Thermal annealing effectively removes this level and improves the QW emission. The concentration of this level is not clearly correlated with N content, suggesting that this level is induced by a low-temperature growth of the GaAsN layer to suppress the composition fluctuation. Given its energy, this level is tentatively assigned to VGa. [ABSTRACT FROM AUTHOR]

Strain relaxation in GaAs/In0.2Ga0.8As/GaAs structures is investigated by analyzing relaxation-induced traps. Strain relaxation is shown to cause carrier depletion by the induction of a 0.53 eV trap in the top GaAs layer, a 0.13 eV trap in the InGaAs layer, and a 0.33 eV trap in the neighboring lower GaAs layer. The 0.53 eV trap which exhibits a logarithmic function of transient capacitance is attributed to threading dislocations. The 0.33 eV trap exhibits an exponential transient capacitance, suggesting a GaAs point defect as its origin. Given its activation energy, it is assigned to the EL6 in GaAs, commonly considered to be Asi-VGa complexes. This trap and the 0.13 eV trap are regarded as the same, since their energy difference is comparable to the optically determined conduction-band offset. The spatial location of this trap correlates with that of misfit dislocations. Accordingly, the production of this trap is determined from the mechanism of strain relaxation. A likely mode of strain relaxation is deduced from the locations of these traps. [ABSTRACT FROM AUTHOR]

Effect of growth rate on the composition fluctuation is investigated in In0.34Ga0.66As0.98N0.02/GaAs single quantum wells (QWs) by photoluminescence (PL), transmission electron microscopy, and admittance spectroscopy. In an InGaAsN layer grown at a normal growth rate, the PL spectra show a low-energy bump at the tail of an InGaAsN emission, suggesting the presence of composition fluctuation. Lowering the growth rate degrades the composition fluctuation by segregating into bimodal phases of an InGaAsN and InGaAs-rich phase. Further lowering the growth rate leads to a three-dimensional growth and enhances the InGaAs-rich phase. The carrier distribution for the InGaAsN layer grown at the normal rate shows a carrier bump at the tail of a strong accumulation peak, suggesting the presence of an electron state below the QW ground state. The admittance spectroscopy shows that the activation energy (32 meV) of this electron state is comparable to the energy separation (30 meV) between the InGaAsN emission and the low-energy bump, and thus it is possible that the composition fluctuation actually induces an electron state closely below the QW ground state. [ABSTRACT FROM AUTHOR]

The conduction and interface states of laterally wet-oxidized GaAs-AlGaAs-GaAs structures after various oxidation times are investigated. Effective current blocking is achieved after 150 min oxidation and the conduction of current through the oxidized AlGaAs layer is controlled by the Poole-Frenkel mechanism, from which a relative dielectric constant of 7.07 is obtained. At an oxidation time of 15 min, capacitance-voltage spectra exhibit capacitance dispersion over frequency, implying the presence of an interface state. The intensity of the dispersion increases with increasing the oxidation time and admittance spectroscopy reveals a significant interface state at ∼0.28 eV at 45 min. Further increasing the oxidation time to 150 min broadens the interface state to a set of continuous interface states from 0.19–0.31 eV with decreasing densities from 3×1011 to 0.9×1011 eV-1 cm-2 and generates fixed charges of about 9.1×1011 cm-2 in the oxidized layer. By comparison to a similar trap in a relaxed InGaAs/GaAs, the interface state is tentatively assigned to the interaction of residual As with dislocations. [ABSTRACT FROM AUTHOR]

We perform capacitance-voltage and admittance spectroscopy to investigate the effect of incorporating an InAlAs layer before an InGaAs cap layer on electron emission in self-assembled InAs quantum dots (QDs). We show that this incorporation of a high potential barrier increases the emission time of the electrons thermally activated from the QD ground to the first excited state. The energy separation between the ground and first excited states in the conduction band increases from 57.2 to 79.1, to 89.2, and to 95.6 meV with increasing the thickness of the InAlAs layer from 0 to 10, to 14, and to 20 Å. Combining with photoluminescence (PL) data, the ratios of the energy separation between the ground and first excited states in the conduction band and valence band are determined to be 7.3:2.7 and 7.8:2.2 for 0 and 10 Å InAlAs, respectively. In addition, this incorporation is shown to blueshift the PL first excited state much larger than the ground state. [ABSTRACT FROM AUTHOR]

This study presents the results of incorporating N into self-assembled InAs quantum dots (QDs) capped with an InGaAs cap layer. Experimental results indicate that such incorporation can redshift the QD ground state and decrease the energy spacing between the QD ground and first excited states. However, this incorporation reduces the potential barrier of the cap layer, increasing the electron escape from the QDs. Capacitance-voltage profiling shows that a broad shoulder corresponding to the electron emission from the QD ground to first-excited state cannot be resolved from the peak related to the electron emission from the excited states upon this incorporation. This finding implies that this incorporation reduces the energy spacing between the QD ground and first-excited states in the conduction band, thus correlating well with the photoluminescence data. In contrast, incorporating N directly into the InAs QD produces no redshift of the emission wavelength but introduces a deep trap at ∼0.21 eV that depletes the electrons in the QDs. [ABSTRACT FROM AUTHOR]

The effect of strain relaxation in a relaxed InAs quantum dot (QD) capped with InGaAs is investigated by admittance and deep-level transient spectroscopy (DLTS). Strain relaxation markedly increases the emission time in the QD region and extends carrier depletion to the bottom GaAs layer. The experimental data show the presence of relaxation traps in the QD region and the neighboring bottom GaAs layer. The electron emission from the QD region is governed by a trap located at 0.17–0.21 eV below the QD ground state. The electron-escape process is identified as thermal activation at high temperatures and direct tunneling at low temperatures from the trap. In the bottom GaAs layer near the QD, DLTS reveals a relaxation trap at 0.37–0.41 eV relative to the GaAs conduction band. The energy difference between these two traps is comparable to the QD ground-state energy relative to the GaAs conduction-band edge, suggesting that the two traps may be the same trap which is pinned to the GaAs conduction band. The considerable difference between their properties may result from different atoms surrounding the trap. [ABSTRACT FROM AUTHOR]

The optoelectronic characteristics of self-assembled InAs quantum dots (QDs) with strain-reduced layers (SRLs) were investigated using photoluminescence (PL) spectroscopy. Various SRLs that combine In0.14Al0.86As and In0.14Ga0.86As with the same total thickness were examined to ascertain their confining effect on carriers in InAs QDs. The emission wavelength is blueshifted as the thickness of InAlAs is increased. The energy separation between the ground state and the first excited state of QDs with InAlAs SRLs greatly exceeds that of QDs with InGaAs SRLs. Atomic force microscopic images and PL spectra of the QD samples demonstrated that high-quality InAs QDs with long emission wavelengths and a large energy separation can be generated by growing a low-temperature, thin InAlAs SRL onto self-assembled QDs. [ABSTRACT FROM AUTHOR]

Presents a study which investigated the electric properties of multiple-quantum-well diodes. Experimental procedures; Results and discussion; Conclusion.

Presents a study that examined an interband tunneling effect between gallium-antimony (GaSb) valence-band and indium-arsenic conduction-band quantum wells in a triple-barrier interband tunneling (TBIT) device. Diagram of a TBIT structure under flatband conditions; Information on the room-temperature current-voltage characteristics of TBIT diodes.

Presents a study which examined the effects of GaSb/InAs/GaSb/AlSb/InAs broken-gap interband tunneling diode. Device design and fabrication of the structure; Characterization of the device; Structural difference of the double-barrier interband tunneling structure.

Analyzes the use of tin-tellurium as a source of donor impurities in the growth of n-type gallium-antimony by moleclar beam epitaxy. Details on the experiment; Effects of source temperature on tellurium incorporation; Electrical properties of tellurium-doped gallium-antimony epilayers.

Examines the dependence of the interband tunneling current on AlSb barrier widths in the InAs/AlSb/GaSb single-barrier diode structures. Overview of the device fabrication; Details on device characterization.

Presents a study which proposed a GaSb/AlSb/GaSb/AlSb/InAs double-barrier interband tunneling diode. Device design and fabrication; Description of the epitaxial layer structures of the device; Characterization of the device.

Presents a study which fabricated an InAs/AlSb/GaSb single-barrier interband tunneling diode by molecular beam epitaxy. Discussion of the transport mechanism in the tunneling structure according to the I-V characteristics as a function of temperature; Reason for the use of AlSb/GaSb/InAs material system in tunneling applications; Room temperature operation of the single-barrier interband tunneling diode.

Presents a study which examined zinc-doped gallium[subx]indium[sub1-x]phosphide grown by metalorganic chemical vapor deposition. Experimental details; Results and discussion; Conclusions.

Presents a study which examined the role of dominant trap in annealed low-temperature grown molecular beam epitaxial GaAs. Analysis of data collected; Growth and fabrication of the molecular beam; Information on how low-temperature layer influences the measured data; How admittance spectroscopy was measured.

Presents a study which investigated the electrical and microstructural characteristics of the titanium contact on silicon. Experimental procedures; Results and discussion; Conclusions.

Discusses the effects of antimony[sub4]/gallium ratios on the electrical properties of gallium antimonide Schottky diodes. Surface state densities relative to the antimony[sub4]/gallium ratios; Relationship of barrier height to metal work function; Effect of antimony[sub4]/gallium ratios on electron mobility.

Presents information on a study which performed capacitance-voltage measurements on the InAs/AlSab/GaSb interband tunneling diode at various frequencies. Structure of the tunneling diode; Details of the conduction band and the associated bound states found in the numerical algorithm; Extraction of the built-in voltage using the capacitance-voltage data under the depletion condition.

In this paper, we report a synthesis of magnetic porous hollow silica nanotubes (MPHSNTs) using sol-gel method. The MPHSNTs were fabricated by coating Fe3O4 nanoparticles and silica on surfactant hexadecyltrimethylammonium bromide (CTAB) modified CaCO3 nanoneedles surface under alkaline condition. CaCO3 nanoneedles and surfactant CTAB are introduced as nanotemplates to form the hollow and porous structures, respectively. After removing CTAB by calcination and etching CaCO3 nanoneedles away in diluted acetic acid, magnetic porous hollow silica nanotubes with Fe3O4 nanoparticles embedded in the silica shell were achieved. The products were characterized by scanning electron microscopy, transmission electron microscopy, and N2 adsorption-desorption isotherms. Superconducting quantum interference device measurement shows that the nanotubes exhibit superparamagnetism property at room temperature and ferromagnetism below the blocking temperature. Toxicity test was also performed for the magnetic nanocarriers, showing good bio-compatibility. Magnetic porous hollow silica nanotubes with advantages of high surface area, good bio-compatibility, and superparamagnetism are one of the novel drug nanocarriers for nanomedicine applications. [ABSTRACT FROM AUTHOR]

Magnetic porous hollow silica nanosphere is a new class of structured nanomaterials for drug delivery. In this paper, we report a synthesis of magnetic porous hollow silica nanospheres (MPHSNs) using CaCO3/Fe3O4 composite nanoparticles and cationic surfactant double templates. Fe3O4 nanoparticles were first mixed into CaCO3 using rotating packed bed forming CaCO3/Fe3O4 composite nanoparticles. Tetraethoxysilane was then added as precursor to form silica layer on the surface of CaCO3/Fe3O4 composite nanoparticles, while hexadecyltrimethylammonium bromide was used as a second template to direct the formation of porous silica shells. After the calcination of the surfactants and etching away CaCO3, MPHSNs were formed with the magnetite nanoparticles remaining in the cores. Transmission electron microscopy was applied for the nanostructure determination. The pore size can be measured by micromeritics analyzer. Magnetic properties of MPHSNs were measured by a superconducting quantum interface device. Zero-field-cooled and field-cooled magnetization data in the temperature range of 5–300 K show that the MPHSNs are superparamagnetism above the blocking temperature and ferromagnetism below the blocking temperature after the calcination. The MPHSNs can be used as potential nanocarriers for targeted delivery and controlled releasing. [ABSTRACT FROM AUTHOR]

Magnetic nanoparticles are usually present in the form of magnetic carriers and used in nanomedicine and biosystem. In this paper, magnetic hollow silica (MHS) nanoparticles were fabricated by a one-step synthesis of Fe3O4 nanoparticles and then coating of silica on nanosized spherical calcium carbonate under alkaline conditions, in which nanosized calcium carbonate (CaCO3, 25–60 nm) was used as a scarified template, tetraethoxysilane as a precursor, and Fe3O4 nanoparticles (∼5 nm), formed in the initial reaction stage, as magnetic agents. The as-synthesized nanoparticles were immersed in a weak acetic acidic solution to remove CaCO3, forming MHS carriers. The nanostructures of the MHS carriers were characterized by scanning electron microscope, transmission electron microscope, and x-ray diffraction. Superconducting quantum interference device measurement exhibited that the MHS nanoparticles were superparamagnetic. Toxicity was tested for MHS carriers using rat brain microvascular endothelial cells. The cells treated with concentration lower than 50 μg/ml of the MHS nanoparticles showed no significant toxicity. After modification by silane coupling agent, the MHS carriers have strong absorption for ibuprofen in nanomedicine field. [ABSTRACT FROM AUTHOR]

Different kinds of nanospheres are used in magnetic nanosphere fabrication for bioapplications. In this paper, we report a successful synthesis of magnetic hollow silica nanospheres (MHSNS). The MHSNS were fabricated with a one step coating of Fe3O4 magnetic nanoparticles sNPsd (∼10 nm) and silica on nanosized (20-100 nm) spherical calcium carbonate sCaCO3d surface under alkaline conditions, in which the nanosized CaCO3 were used as nanotemplates and tetraethoxysilane and magnetic NPs were used as precursors. The as-synthesized nanoshperes were immersed in an acidic solution to remove nanosized CaCO3, forming MHSNS. The MHSNS were characterized by SEM, TEM, and SQUID. SEM and TEM results showed that a smooth surface of MHSNS and a thin layer of silica (∼10 nm) embedded with the magnetic NPs was successfully formed. No nanosized CaCO3 nanotemplates were observed. SQUID measurement demonstrated that magnetization of MHSNS was dependent on temperature, exhibiting superparamagnetism. The MHSNS have potential applications in biomedicine and bioseparation. [ABSTRACT FROM AUTHOR]

Presents information on a study which investigated the transition of carrier distribution from the strained to the relaxed state in InGaAs/GaAs quantum wells by measuring capacitance voltage and analyzing x-ray diffraction. Carrier distribution of the quantum wells; Correlation between the carrier distribution and critical thickness of InGaAs/GaAs quantum wells.

Presents a study which investigated interband tunneling transport through a hole well in GaSb/AlSb/GaSb/AlSb/InAs II tunnel devices. Discussion on the interband tunneling concept; Effect of the hydrostatic pressures and magnetic fields on the current-voltage characteristics; Calculations of the valence subbands in the quantum well of the sample; Description of the elastic scattering potential strengthen by variation of barrier width.

Describes vertical cavity surface emitting (VCSE) lasers of gallium arsenide (GaAs) active regions and In[sub0.1]Ga[sub0.9]As-GaAs active regions. Purpose of the silver mirror; Information on the room temperature spectral characteristics of the VSCE.