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Triboelectric nanogenerators (TENGs) have been widely investigated to harness mechanical energy that is driven by repetitive human motion. Conventional human motion-driven TENGs are mostly based on contact–separation (CS) mode, but their energy harvesting performance is limited due to the high crest factor (the ratio of the peak to the RMS value of output voltage). Here, we demonstrate a new rolling type triboelectric nanogenerator (RL-TENG), exhibiting the lower crest factor than CS mode TENGs, using a metal layer and graphene nanoplatelets-doped PDMS. These additions helped improve the dielectric constant and the charge storage capacity of the TENG, which led to a high electrical output while minimizing surface damage. As compared to a pristine TENG, our device, a RL-TENG, generated an open-circuit peak voltage of 75.2 V, which was almost 15 times higher than that of the pristine device, and a short-circuit peak current of 7.36μA, which was 12 times higher. With a dual-side double-belt TENG (DB-TENG), these values were improved to 164 V and 10μA. Lastly, our device was used in a real-life application, to harvest mechanical energy from the movement of the human elbow while walking, and was able to produce a high voltage output of up to 821 V. These results show that the DB-TENG can be used for high-efficiency harvesting of energy from human motion.

A novel deep-blue emissive dopant material, 2,7-bis(9,9-dimethylacridine-10(9H)-yl)-9,9-diphenyl-9H-thioxanthene 10-,10-dioxide (DMA-ThX), is synthesized for use in highly-efficient thermally activated delayed fluorescence organic light-emitting devices (TADF OLEDs). The molecular design of DMA-ThX retains the overlap between the lowest singlet excited state (S1) and the lowest triplet excited state (T1) because of its twisted molecular structure. From photoluminescence emission measurements at low temperature, the difference between the S1 and the T1 energy levels of DMA-ThX is found to be 0.07 eV. Furthermore, the external quantum efficiency of the deep-blue-emitting TADF OLEDs with DMA-ThX-doped bis[2-(diphenylphosphino)phenyl] ether oxide is 18.4%, which is significant, and the Commission Internationale de l'Eclairage coordinates are (0.14, 0.14), indicative of very pure deep-blue emission.

CsPbBr3 quantum dots (QDs)-NOA63 nanocomposites (NCs) are fabricated by using a UV-initiated thiol−ene “click” reaction, and the hydrophobic CsPbBr3 QDs are successfully embedded in the NOA63 matrix without chemical decomposition. The CsPbBr3 QDs-NOA63 NCs are utilized as a piezoelectric layer for piezoelectric nanogenerators (PENGs), which are compared with PENGs based on NOA63 and on CsPbBr3 QDs. The average output voltages of the PENGs based on the CsPbBr3 QDs-NOA63 NCs is significantly larger than that of the PENGs with CsPbBr3 QDs alone by a factor of 5.55. The significantly higher output voltages of the PENGs based on the CsPbBr3 QDs-NOA63 NCs is attributed to the very large piezoelectric coupling efficiency due to the utilization of NOA63. Moreover, such PENGs are found to have advantages such as an effective stress transfer, a morphology passivation effect and an enhanced piezoelectric response, and chemical compatibility with CsPbBr3 QDs.

The effects of taper angle of the string and the number of layers on the electrical characteristics of vertical NAND flash memories are investigated. Simulation results show that the transconductance and the threshold voltage distribution over the position of the cell along the string depend on taper angle and the number of layers. There is a taper angle that minimizes the spread of threshold voltage, and hence, the impact of the random telegraph noise and this angle depends on the number of layers. These results will be helpful in designing the vertical NAND flash memories.

Neutron reflectometry was used to determine the thickness of large-area graphene layers on SiO2/Si substrates. Preliminary simulations showed that the optimum thickness of the SiO2 layer for neutron reflection is about a few hundred angstroms. The thicknesses of the graphene and the SiO2 layers were obtained by fitting the experimental reflectivity spectra. Transmission electron microscopy and Raman experiments were performed on the same samples, and verified that the neutron reflection results are reliable and accurate at the subangstrom level. This neutron reflectometry is nondestructive and applicable to wafer-size layers to yield the mean thickness. This accurate determination of the thickness will be helpful for managing quality of large-area graphene films.

We fabricated triboelectric nanogenerators (TENGs) consisting of an Al electrode, a polyimide dielectric layer, a ZnO dielectric layer, and an indium tin oxide (ITO) electrode, and we observed an enhancement of the output voltage that was due to Al doping in the ZnO layer. The variation in the surface of the Al doped zinc oxide (AZO) layer, which was found to depend on the Al doping concentration, was studied by using scanning electron microscopy. The existence of Al particles was identified from the X-ray photoelectron spectroscopy results. The open-circuit voltage and the short-circuit current of the TENGs with 2% and 5% Al doping in the ZnO layer and operating in the vertical contact-separation mode were larger than those of TENGs having a ZnO layer without Al doping, respectively. The Al doping reduced the asymmetry of negative and positive output voltages and shortened the duration of the positive peaks. The enhancement in the output properties of the TENGs due to the dielectric properties of the Al particles, which was theoretically analyzed in the contact-separation mode operated TENGs with dimensionless formulations, which is compared with the experimental results.

We have fabricated flexible, transparent, ultra-thin silver (Ag) electrodes by using a maskless deposition process and applied them to organic light-emitting devices (OLEDs). A selective ultraviolet/ozone (UV/O3) treatment was performed on the polyethylenimine (PEI) polymer layer, which contained amine groups and was coated onto a silicon substrate, in order to form an electrode pattern. An ultra-thin Ag film was deposited in vacuum on the UV/O3-treated substrate without a mask, resulting in the formation of a flexible, transparent, ultra-thin Ag electrode pattern. The optimum PEI concentration and the optimum UV/O3 treatment time for the formation of flexible, transparent, Ag electrode patterns were determined from their sheet resistances, optical transmittances, Fourier-transform infrared spectra and X-ray photoelectron spectra. The sheet resistance of the ultra-thin Ag electrode transferred to an epoxy substrate changed within 5% only when the bending diameter of curvature and the number of bending cycles were 5 mm and 3000, respectively. The current density and the luminance of an OLED with a flexible, transparent, ultra-thin Ag electrode deposited on an epoxy substrate were larger than those of an OLED with an indium-tin-oxide (ITO) electrode formed on a polyethylene naphthalate substrate. We have confirmed that the flexible, transparent, ultra-thin Ag electrodes hold promise for use in the fabrication of flexible OLEDs.

The deterioration of the electrical characteristics of charge trap flash (CTF) memories with a silicon-oxide-nitride-oxide-silicon (SONOS) structure due to the charge traps in the oxide layers attributed to the random trapping and detrapping processes was investigated. Simulation results for the CTF memories showed that the threshold voltage shift was decreased by the charge trapped in the oxide layers in the SONOS structure and that the charge trapped in the blocking oxide had more significant effects than that trapped in the tunneling oxide. The degradation effects of the charge trapped in the blocking oxide on the electrical characteristics of the CTF memories were clarified by examining the vertical electric field in the device.

The electrical characteristics of NAND flash memories with a high-k dielectric layer were simulated by using a full three-dimensional technology computer-aided design simulator. The occurrence rate of the errors in the flash memories increases with increasing program/erase cycles. To verify the word line stress effect, electron density in the floating gate of target cell and non-target cell, the drain current in the channel of non-target cell and depletion region of the non-target cell were simulated as a function of program/erase cycle, for various floating gate thicknesses. The electron density in the floating gate became decreased with increasing program/erase cycles. The reliability degradation occured by the increased depletion region at the bottom of the polysilicon floating gate in the continued program/erase cycle situation due to the word line stress. The degradation mechanisms for the program characteristics of 20-nm NAND flash memories were clarified by examining electron density, darin current and depletion region.

CdSe/CdS/ZnS core-shell-shell quantum dots (QDs) were synthesized by using a solution process. High-resolution transmission electron microscopy images and energy dispersive spectroscopy profiles confirmed that stoichiometric CdSe/CdS/ZnS core-shell-shell QDs were formed. Ultraviolet-visible absorption and photoluminescence (PL) spectra of CdSe/CdS/ZnS core-shell-shell QDs showed the dominant excitonic transitions from the ground electronic subband to the ground hole subband (1S(e)-1S(3/2)(h)). The PL mechanism is suggested; the carriers generated by the exciting high-energy photons in the shell region are relaxed to the band-edge states of the core region and recombined to emit lower-energy photons. The activation energy of the carriers confined in the CdSe/CdS/ZnS core-shell-shell QDs, as obtained from temperature-dependent PL spectra, was 200 meV. The quantum efficiency of the CdSe/CdS/ZnS core-shell-shell QDs at 300 K was estimated to be approximately 57%. (C)2015 Optical Society of America

Phosphorescent white organic light-emitting devices (Ph-WOLEDs) fabricated utilizing carbazole/thioxanthene-S,S-dioxide (EBCz-ThX) host material were investigated to enhance their efficiency by understanding the energy transfer process from the host to the dopant materials. Time-resolved photoluminescence (PL) spectra at room and low temperatures demonstrated that the energy transfer occurs between the EBCz-ThX host and the bis(2-benzo[b]thiophen-2-ylpyridine)(acetylacetonate)-iridium(III) (Ir(bt)2acac) orange dopant or the (bis(2-(4,6-difluorophenyl)pyridyl-N,C2′)iridium(III) picolinate (FIrpic) blue dopant. The energy transfer process was inferred from the PL decay curves of Ir(bt)2acac doped EBCz-ThX with doping concentrations of 5, 10, and 20%. The quantum efficiency in the Ph-WOLEDs with 5% Ir(bt)2acac doped EBCz-ThX is the highest since its energy transfer process from EBCz-ThX to Ir(bt)2acac involves the charge transfer states and is most efficient. The quantum efficiency of the Ph-WOLEDs with 5% Ir(bt)2acac doped EBCz-ThX emission layers at 1,000 cd/m2 showed the highest value of 10.2%, and the commission internationale de l'Eclairage (CIE) coordinates were (0.45, 0.46), indicative of the warm white emission.

We present a simple approach to the evaluation of strain in zinc blende and in wurtzite layered semiconductor structures. These crystallographic structures are of particular interest because of their importance in optoelectronic device applications. The composite layered materials are currently grown pseudomorphically on substrates, which dictate the strain in the layers. Components of the strain are derived for arbitrary crystallographic growth directions. The strain in the layer determines the piezoelectric field in each layer in the structure. The strain and the strain-induced electric field are important in designing layered heterostructures with specific electronic energy levels for device applications. The methods presented are more generally applicable to other crystallographic structures and composite pseudomorphically grown materials. Illustrative problems and solutions are included.

The authors successfully obtained high quality ZnO thin films by growing them at room temperature (RT) and postannealing by rapid thermal annealing (RTA). The thin films were grown by pulsed laser deposition on Si (100) substrates at RT, and RTA was performed under various temperatures and ambient conditions. Based on the UV emission to visible emission ratio in RT photoluminescence (PL) spectra, the optimum film was obtained at annealing temperature ∼700 °C in an ambient of Ar, N2, or O2 at 0.1 Torr, while the optimum annealing temperature was above 1100 °C in the air ambient at atmospheric pressure. The morphology and structure of the films in different RTA conditions were investigated by using field emission scanning electron microscopy and grazing incidence x-ray diffraction, and were discussed in conjunction with the PL data.

ZnO thin films were grown on Si (100) substrates by pulsed laser deposition using a ZnO target. The substrate temperature was varied in the range of room temperature to 800°C, and the oxygen partial pressure of 0.1333 Pa (1 mTorr) to 1333 Pa (10 Torr). The properties of the resulting films were investigated by photoluminescence (PL), grazing incidence X-ray diffraction (GIXRD), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (FESEM). Based on the ultraviolet (UV, ∼380 nm) to visible emission ratio in the PL spectrum, the optimum growth conditions were determined to be 600°C and 133.3 Pa (1 Torr), respectively. The oxygen 1 s peak in the XPS spectrum was decomposed into two peaks. The peak at lower binding energy increased in intensity with the oxygen partial pressure from 0.1333 Pa (1 mTorr) to 133.3 Pa (1 Torr) while the other peak decreased. The GIXRD curve at the optimum condition showed strong two peaks (002 and (103). A strong correlation between the (103) peak intensity and the UV emission intensity was found.

We demonstrated the successful fabrication of MgO-core/ZnO-shell nanowires, in which the shell layers were deposited by using the sputtering technique. Transmission electron microscopy investigations revealed that core nanowires were surrounded by a ZnO shell layer. At 298 K, the photoluminescence (PL) peak intensity ratio (green/UV) decreased with increasing ZnO shell thickness. In regard to the effect of temperature, the intensity of the green emission band was progressively decreased with increasing measurement temperature. We discuss the possible associated PL emission mechanisms.

The spin states of electrons in a perpendicular magnetic field (B) are studied with the introduction of anisotropic harmonic confinement and spin-orbit coupling (SOC) (both Dresselhaus and Rashba interactions). The effective g-factors, as well as B-dependence of subbands, are numerically calculated for GaAs and their dependence on confinement strength and degree of anisotropy is estimated. This model is in good agreement with previous reports [PRB 72, 155410 (2005) and so on] in the isotropic limit and weak SOC, indicating its usefulness for slightly deformed quantum dots and short quantum wire. However, dispersion caused by mixing of spin states imposes limitations when SOC and confinement are comparable.

We present the theoretical basis of wavefunction engineering. We show that a Lagrangian formulation for the valence bands of bulk semiconductors in the k · P model provides a direct approach to determining derivative operator ordering in the multiband description of electronic states in semiconductors in the envelope function approximation. The current continuity condition is also obtained through a gauge variation on the Lagrangian. This naturally leads

Transmission electron microscopy (TEM) and photocurrent (PC) measurements were carried out to investigate the microstructural properties and excitonic transitions in InxGa1−xAs/In0.52Al0.48As multiple quantum wells (MQWs) for x = 0.54, 0.57 and 0.60. TEM images showed that high-quality 11-period InxGa1−xAs/In0.52Al0.48As MQWs had high-quality heterointerfaces. The results for the PC spectra at 300 K showed that the peaks corresponding to the excitonic transitions from the ground state electronic sub-band to the ground state heavy-hole band (E1-HH1) and the ground state electronic sub-band to the ground state light-hole band (E1-LH1) became closer to each other with decreasing In mole fraction and that E1-HH1 and E1-LH1 excitonic peaks shifted to longer wavelength with increasing applied electric field. The calculated values of the E1-HH1 interband transition energies were in qualitative agreement with those obtained form the PC measurements with and without applied electric field. These results can be helpful in understanding potential applications of InxGa1−xAs/InyAl1−yAs MQWs dependent on In mole fraction and applied electric field in long-wavelength optoelectronic devices.

Unlike for the bound states, several different boundary conditions are used for the continuum states above the barrier in semiconductor quantum wells. We employed three boundary conditions, infinite potential barrier boundary condition, periodic boundary condition and scattering boundary condition, and calculated the local number of states, wavefunctions and optical matrix elements for the symmetric and asymmetric quantum wells. We discussed how these quantities are related in the three boundary conditions. We argue that the scattering boundary condition has several advantages over the other two cases. These results would be useful in understanding quantum well lasers and detectors involving continuum states.

We have investigated the optical properties of InAs self-assembled quantum dots (SAQDs) with the Si-doped GaAs barrier layer. Two types of samples are fabricated according to the position of the Si-doped GaAs layer. For type A samples the Si-doped GaAs layer is grown below the QDs, whereas for type B samples the Si-doped GaAs layer is grown above the QDs. For both types of samples the excited-state emissions caused by state filling are observed in photoluminescence (PL) spectra at high excitation power densities. The bandgap renormalization of QDs can be found from the shift of the PL peak energy. Particularly, for type A samples the Si atoms act as nucleation centers during the growth of InAs QDs on the Si-doped GaAs layer and affect the density and the size of the QDs. The Si-doped GaAs layer in type A samples has more effects on the properties of QDs, such as state filling and bandgap renormalization than those of type B samples.

In this paper, we present a new flicker evaluation model through the electrical simulation of the optical flicker phenomena in different kinds of poly-Si TFT-LCD arrays for the development and manufacturing of large-area and high-quality TFT-LCDs. We applied our flicker evaluation model to three different types of TFTs; excimer laser annealed (ELA) poly-Si TFT, silicide mediated crystallization (SMC) poly-Si TFT, and counter-doped lateral body terminal (LBT) poly-Si TFT. We compared the flicker quantitatively for these three different TFT-LCDs on 40 in. UXGA scale. We identified three major factors causing the flicker such as charging time, kickback voltage and leakage current, analyzed their relative contributions to the flicker, and evaluated the values of the flicker in decibel (dB) for the three different TFT-LCD arrays. In addition, we show that the flicker is very sensitive to the low-level (minimum) gate voltage due to the large leakage current of the poly-Si TFT, and the low-level gate voltage should be chosen carefully to minimize the flicker.

Post-growth rapid thermal annealing (RTA) has been used to investigate an interdiffusion and the structural change in an InGaAs dots-in-a-well (DWELL) structure grown by molecular beam epitaxy using an alternately supplying InAs and GaAs sources. In the case of the as-grown sample, which has a metastable quantum structure due to an intentional deficit of source materials, it is found that an InGaAs quantum well (QW) coexists with the premature quantum dots (QDs), and an intermediate layer exists between the QW and the QDs. Through the RTA process at 600 and 800°C for 30s, metastable structure changes into a normal DWELL structure composed of QDs and QW as a result of the intermixing of premature QDs and the intermediate layer.

We have investigated the electrical and optical properties of the modulation-doped InAs quantum dots (QDs) by alternately supplying In and As sources. Three different samples are fabricated according to the doping concentration of the Si-doped GaAs layer. All the samples show the excited state emissions as well as the ground state emission in photoluminescence (PL) spectra due to the state filling by the electrons supplied from the doped GaAs layer. For a low doping concentration the transition from the first excited electron state to the first excited hole state (E1–H1) is apparent together with the ground state transition (E0–H0). These PL emissions increase with the similar rate as the excitation power density increases. For higher doping concentrations the ground state transition and the transition from the first excited electron state to the ground hole state (E1–H0) are apparent at a low excitation power density. As the excitation power density increases, the E1–H1 transition becomes dominant rather than the E1–H0 transition. In the capacitance-voltage (C–V) result for the sample with a low doping concentration, the characteristic steps due to the accumulation of electrons are observed. For the sample with higher doping concentrations the characteristic step is not found in C–V curves, which is associated with the state filling of QDs.

We fabricated Er-doped silicon-rich silicon oxide (SRSO:Er) films by pulsed laser deposition. A Si+Er target consisting of an Er metallic strip and a silicon disk was adopted with a goal to achieve a convenient control of the Er and oxygen density in the film. We found that the photoluminescence (PL) at 1.54 μm is highly dependent on the ambient oxygen pressure, which determines the relative ratio of Si-Si, SiOx, and SiO2 phase in the film. The PL intensity increased drastically with increase in the annealing temperature and reached the maximum intensity at 500 °C.

We investigated the electrical and optical properties of InGaAs self-assembled quantum dots grown using the atomic layer epitaxy (ALE) technique. Dots–in–a–well structures were grown by alternately supplying InAs and GaAs sources on an InGaAs layer and covering with another InGaAs layer. Three samples produced with different numbers of cycles of alternate InAs/GaAs supply were characterized by capacitance-voltage and photoluminescence (PL) measurements. For the ten cycle dots–in–a–well structure, a strong zero-dimensional electron confinement was observed even at room temperature. On the other hand, for the five-cycle structure, the PL results indicate that the InGaAs quantum well structure coexists unstably with premature quantum dots. By comparing the results for samples with different numbers of cycles, we suggest that an ALE dots–in–a–well structure can be formed by the aggregation of In and Ga atoms incorporated into the InGaAs quantum well layer when the number of cycles exceeds the critical number ...

II–VI/III–V heterostructures based on wide-energy band-gap II–VI compound semiconductors have been very attractive because of their potential applications in short-wavelength optoelectronic devices [1–5]. Among these II–VI/III–V mixed heterostructures, ZnSe/GaAs heterostructures have been particularly interesting due to their promising applications for the fabrication of laser diodes and light-emitting diodes operating in the blue-green region of the spectrum [6–10]. However, relatively little work has been performed on II–VI/III–V heterostructures in comparison with III–V/III–V heterostructures due to cross-doping problems resulting from interdiffusion or intermixing during growth and fabrication [11]. Since thermal treatment is necessary for the fabrication processes of several kinds of optoelectronic devices utilizing ZnSe/GaAs heterostructures, the role of the thermal annealing processes is very important in achieving high-performance devices [12]. Therefore, studies of the annealing effects on the surface, the structural, and the optical properties play a very important role in enhancing device efficiency. This letter reports the effect of annealing of ptype ZnSe epilayers grown on n-type GaAs (100) substrates by using molecular beam epitaxy (MBE). Atomic force microscopy (AFM), photoluminescence (PL), and transmission electron microscopy (TEM) measurements were performed in order to investigate the surface, the optical, and the structural properties of as-grown and annealed ZnSe/GaAs heterostructures. The samples used in this study were p-type ZnSe epitaxial layers grown on n-type GaAs (100) substrates in a Riber 32 P system by using MBE. Elemental Zn and Se with purities of 99.9999% were used as the source materials, and the flux ratio, Zn/Se, was approximately 0.5 during ZnSe epilayer growth. The p-type doping was carried out using an rf plasma source to excite nitrogen gas at a pressure of 10−8 Torr in the

Er-doped SiOx thin films were fabricated by laser ablation of a Si:Er2O3 target in He atmosphere. We have measured the photoluminescence (PL) at 1.54 μm for the films grown at different He pressures and found that the oxygen density of the grown film that strongly influences the PL intensity is highly correlated with the ambient He pressure. This manifests that oxygen density of the film can be controlled in an inert atmosphere to maximize PL intensity when we adopt pulsed laser deposition (PLD) technique to deposit Er-doped SiOx thin films. Also, we have examined the temperature dependence of PL and observed that the thermal quenching is greatly reduced for the PLD-grown films.

Electrochemical deposition was employed to fabricate Cu2O nanocubes on indium-tin-oxide (ITO)-coated glass substrates at 75 °C without using any template, catalyst, or seed layer. Scanning electron microscopy images showed that the Cu2O nanocubes with a nanoscale size were uniformly formed on ITO-coated glass substrates. X-ray patterns of the Cu2O nanocubes exhibited the dominant peaks corresponding to the Cu2O cubic structures. The current–voltage curves of an Au/n-type Al-doped ZnO/p-type Cu2O nanocube/ITO device clearly showed current rectifying behavior with a turn-on voltage of 3.6 V.

We have synthesized PPV derivative containing an adamantane side group, poly(1-(2-ethylhexyloxy)-4-(1-adamantaneethyloxy)-2,5-phenylenevinylene, EHAE-PPV) and fabricated the segment device using this polymeric electroluminescent material. EHAE-PPV is solution processable and shows high photoluminescence intensity, probably due to the steric effect of the adamantyl group. This polymer also has exhibited good electroluminescent properties.

Electronic property variations of a two-dimensional electron gas (2DEG) in modulation-doped step quantum wells due to an embedded potential barrier were studied by performing Shubnikov–de Haas (SdH), Van der Pauw–Hall-effect, and cyclotron resonance measurements on two kinds of InxGa1−xAs/InyAl1−yAs step quantum wells which were one without and the other with an embedded barrier. The fast Fourier transformation results for the SdH data at 1.5 K indicated the electron occupation of two subbands in both step quantum wells. The total electron carrier density and the mobility of the 2DEG in the step quantum well with an embedded barrier were smaller than those in the quantum well without an embedded barrier. The electron effective masses were determined from the slopes of the main peak absorption energies as functions of the magnetic field, and satisfied qualitatively the nonparabolicity effects in both quantum wells. The electronic subband energies, the wave functions, and the Fermi energies were calculated ...

Ion beam-assisted deposition of Ni on p-InP (100) at room temperature was performed in order to produce Ni thin films with high quality and Ni/p-InP (100) heterostructures with abrupt heterointerfaces. An atomic force microscopy image showed that the root mean square of the average surface roughness of the Ni film was 21.3 A, and x-ray diffraction and transmission electron microscopy (TEM) measurements show that Ni film layers grown on InP (100) substrates were polycrystalline. Auger electron spectroscopy and TEM measurements showed that Ni films grown on p-InP (100) substrates at room temperature had no significant interdiffusion problems. The work function of the Ni thin film was determined from the secondary electron emission coefficients obtained with a focused ion beam. These results provide important information on the microstructural and electronic properties for Ni thin films grown on p-InP (100) substrates at room temperature.

The Shubnikov–de Haas (S–dH) measurements at 1.5 K clearly demonstrated the existence of a two-dimensional electron gas (2DEG) in the modulation-doped Al0.25Ga0.75As/InyGa1−yAs/GaAs single and step quantum wells, and the fast Fourier transformation results for the S–dH data clearly indicated the electron occupation of one subband in the asymmetric single and step quantum wells. While the electron carrier density of the 2DEG in the step quantum well was larger than that in the single quantum well due to the larger conduction-band discontinuities, the mobility of the 2DEG in the step quantum well was smaller than that in the single quantum well because of the interface scattering resulting from the embedded step well. The electron effective mass in the step quantum well was smaller than that in the single quantum well, which was consistent with a smaller mass of the embedded deep step layer. The electronic subband energy, the energy wave function, and the Fermi energy in the InyGa1−yAs step quantum wells we...

The effect of the side group, employed during synthesis, on the PL (photoluminescence), EL (electroluminescence) profiles and the light intensity of PPV derivatives has been investigated using MEH (methoxy-ethyl-hexyloxy) and MCHM (methoxy-cyclo-hexyl-methyloxy) as side groups. The measurements show that even the most subtle change in molecular structure of PPV has a marked improvement on the EL, PL profiles and the light emission intensity. It has been found that the PL and EL intensities of the MCHM-PPV are higher than those of MEH-PPV. MCHM-PPV also demonstrated higher light emission at lower potentials and currents.

Pd layers were grown on p-InP (100) substrates by the ion-beam-assisted deposition method with the goal of producing sharp Pd/p-InP heterostructure interfaces. X-ray diffraction measurements showed that the grown Pd layer was polycrystalline. Auger electron spectroscopy measurements showed that the composition of the as-grown film was Pd and that the Pd/InP interface quality was relatively good. Transmission electron microscopy measurements showed that the grown Pd was a polycrystalline layer. The growth of polycrystalline Pd layers, instead of epitaxial films, originated from the formation of an interfacial amorphous layer prior to the creation of the Pd films. These results indicate that the Pd layers grown on p-InP (100) can be used for stable contacts in optoelectronic devices and high-speed field-effect transistors based on InP substrates and that the deposition of Pd on InP at room temperature might increase the barrier height of the resulting Pd/InP Schottky diode.

Single crystal films of ZnSe have been grown on nonpolar GaAs(1 1 0) surfaces by molecular beam epitaxy (MBE). The epitaxial films have been characterized by in situ reflection high-energy electron diffraction (RHEED), ex situ scanning electron microscopy (SEM) and X-ray diffraction. RHEED and SEM images of the surfaces reveal the formation of facets which are aligned along the [0 0 1] direction. The formation of facets indicates that ZnSe growth on the (1 1 0) surface proceeds 6°–13° off the vicinal (1 1 0) surface. Facet-free ZnSe surface has been successfully grown on a GaAs(1 1 0) 6°-off the substrate.