Yoshimine Kato

Thermally Activated Delayed Fluorescence from Sn4+–Porphyrin Complexes and Their Application to Organic Light Emitting Diodes — A Novel Mechanism for Electroluminescence

[*] Prof. C. Adachi, A. Endo, Dr. D. Yokoyama Center for Future Chemistry Kyushu University 744 Motooka Nishi, Fukuoka 819-0395 (Japan) E-mail: adachi@cstf.kyushu-u.ac.jp M. Ogasawara, Prof. Y. Kato Department of Materials Science and Engineering Kyushu University 744 Motooka Nishi, Fukuoka 819-0395 (Japan) Dr. A. Takahashi Sogo Pharmaceutical Co., Ltd. Hebinami 28-3, Johban Shimofunao Iwaki, Fukushima 972-8312 (Japan) [+] Present address: Mitsubishi Chemical Group Science and Technology Research Center, Inc., Display Project, Research and Development Division, 1000 Kamoshida-cho, Aoba-ku, Yokohama 227-8502, Japan.

Gas-source molecular beam epitaxy and luminescence characterization of strained Si1−xGex/Si quantum wells

Abstract We describe gas-source molecular beam epitaxy (MBE) and luminescence characterization of strain Si 1− x Ge x /Si quantum wells (QWs). Successful and reproducible growth of strained QWs is demonstrated, addressing the significance of selecting a higher growth temperature to establish a high degree of structural integrity and to maintain the crystallinity in terms of “optical” quality. Excellent heterointerface transcience was evidenced by an almost perfect match between the spectral shift due to exciton confinement and the theoretical calculation. A good spatial uniformity in terms of well width and composition was obtained when QWs are grown in the adsorption/dissociation-limited growth regime.

The effect of electric field on the excitonic states in coupled quantum well structures

We have calculated by a variational procedure the excitonic states in symmetric coupled quantum well structures of GaAs/AlGaAs in the presence of an external electric field perpendicular to the interfacial plane using a nonseparable, nonspherical hydrogenic trial wavefunction. The exciton binding energies have been calculated as a function of external electric field for various well and barrier widths. The nonspherical trial wavefunction leads to a better estimate of the exciton binding energy, especially in high electric field, than that calculated with a spherical one. The calculations show that the binding energy is strongly dependent on the external electric fields: the variation (increase or decrease) is related to the spatial distribution of the wavefunctions. The results of the calculation are consistent with our experimental results.

Photoenhanced chemical vapor deposition of zinc phosphide

Thin films of zinc, phosphorus, and zinc phosphide (Zn3P2) have been deposited by photodissociation of dimethylzinc (DMZ) and phosphine (PH3) on various substrates using a low‐pressure mercury lamp as a light source. The substrate temperature was varied between room temperature and 250 °C. The deposition rates of the films were significantly affected by the UV light intensity, the density of gases, the PH3/DMZ molar ratio, and the substrate temperature. Zn3P2 microcrystallites were grown on Si(111) substrates at a temperature of 250 °C. Those crystallites were studied by using a scanning electron microscope and reflection high‐energy electron diffraction. A very weak photoluminescence spectrum at 808 nm (1.53 eV) was observed at room temperature.

Hybrid Si molecular beam epitaxial regrowth for a strained Si1−xGex/Si single‐quantum‐well electroluminescent device

An n‐type Si contact layer for an electroluminescent (EL) diode was successfully grown on a Si/Si1−xGex/Si single‐quantum‐well (SQW) structure by ‘‘hybrid’’ Si molecular beam epitaxy (MBE) for the first time. The hybrid MBE was performed by regrowing the Si contact layer in a solid‐source MBE chamber after transferring the SQW sample through air from a gas‐source (GS) MBE chamber, in which the starting SQW structure was grown. A (2×1) reconstruction was observed on a GSMBE‐prepared Si(100) surface even after the SQW sample was exposed to air for up to 15 h. An excellent quality of the EL device was evidenced by the sharpest emission lines ever reported in the EL spectra of SiGe system. The spectral features of the EL and photoluminescence were found to be almost identical, and a well‐resolved acoustic phonon replica was observed.

56.1: Novel LC Alignment Method using Diamond Like Carbon Film and Ion Beam Alignment

A novel LC alignment method has been developed. In this, the conventional polyimide film and cloth rubbing have been replaced by a diamond-like-carbon film and an ion beam respectively. The novel method has been used in pilot-line manufacturing to produce super high quality panels: 15″ TN mode and 22″ IPS mode. These panels will be demonstrated, and the advantage of new method will be discussed.

Effects of annealing on anodic oxides of GaP

The surface topography and the chemical composition of anodic oxides on GaP have been studied. The surface of the as grown anodic oxide was featureless but annealing at T≥600 °C causes the formation of hollow bumps and blisters which increase in size with temperature or duration of the anneal. The oxide composition was investigated by x‐ray photoelectron spectroscopy (XPS) and was found to be a nonuniform mixture of P2O5, Ga2O3, and GaPO4. There is some evaporation of phosphorus oxide near the surface when annealed at T≥300 °C but little or none from the bulk of the oxide film.The surface topography and the chemical composition of anodic oxides on GaP have been studied. The surface of the as grown anodic oxide was featureless but annealing at T≥600 °C causes the formation of hollow bumps and blisters which increase in size with temperature or duration of the anneal. The oxide composition was investigated by x‐ray photoelectron spectroscopy (XPS) and was found to be a nonuniform mixture of P2O5, Ga2O3, and GaPO4. There is some evaporation of phosphorus oxide near the surface when annealed at T≥300 °C but little or none from the bulk of the oxide film.

Rectification properties of n-type nanocrystalline diamond heterojunctions to p-type silicon carbide at high temperatures

Highly rectifying heterojunctions of n-type nanocrystalline diamond (NCD) films to p-type 4H-SiC substrates are fabricated to develop p-n junction diodes operable at high temperatures. In reverse bias condition, a potential barrier for holes at the interface prevents the injection of reverse leakage current from the NCD into the SiC and achieves the high rectification ratios of the order of 10{sup 7} at room temperature and 10{sup 4} even at 570 K. The mechanism of the forward current injection is described with the upward shift of the defect energy levels in the NCD to the conduction band of the SiC by forward biasing. The forward current shows different behavior from typical SiC Schottky diodes at high temperatures.

Postgrowth of a Si contact layer on an air-exposed Si1-xGex/Si single quantum well grown by gas-source molecular beam epitaxy, for use in an electroluminescent device

A Si contact layer for an electroluminescent (EL) diode was successfully grown on a Si1−xGex/Si single quantum well (SQW) layer by ‘‘hybrid’’ Si molecular beam epitaxy (MBE). The ‘‘hybrid’’ MBE was performed by growing the Si contact layer in a solid‐source MBE chamber after transferring the sample through air from a gas‐source MBE (GSMBE) chamber in which the starting SQW layer was initially grown by using disilane (Si2H6) and germane (GeH4). The growth characteristics of the hybrid MBE were investigated by in situ monitoring of the reflection high energy electron diffraction. A (2×1) reconstruction was observed even after the sample was exposed to air for up to 15 h on a GSMBE‐prepared Si(100) surface. Evidence of the excellent quality of the EL device was provided by the sharpest emission lines, a full width at half maximum of ≊5.5 meV. The spectral features of the EL and photoluminescence were found to be almost identical, and a well‐resolved acoustic phonon replica was observed. Linear polarization f...

Observation of the Stark effect in coupled quantum wells by electroluminescence and circularly polarized photoluminescence excitation spectroscopy

Successful observation is reported of the quantum‐confined Stark effect in electroluminescence (EL) under a ‘‘forward’’ electric‐field condition, with a current injected into a p‐i‐n diode containing Al0.3Ga0.7As/GaAs symmetric coupled double quantum wells (CDQWs). The Stark shift observed in EL and (under a reverse bias) in photoluminescence (PL), in both of which the transitions involved are between the electron and heavy‐hole lowest states, is found to be symmetrical with respect to the flatband bias, in agreement with calculations. The origin of the optical transitions between electron and light‐ or heavy‐hole states in the CDQWs is also clearly identified by a combination of PL and circularly polarized photoluminescence excitation spectra.