Modified multilayer quantum dots (MQDs) structures are fabricated on GaAs (311)A substrates. QD lavers are self-formed by growing (GaP)(1.5)(InP)(1.88) short-period superlattices (SLs). By the use of InGaP/InAlP SL lavers as barrier and cladding lavers instead of InGaP layers, the optical properties are much unproved, which is mainly due to the improved carrier confinement and the reduction of carrier overflow by the increase in band offset. The current injection laser operation is observed for the laser diodes with these MQDs as an active layer.

Absorption spectra of the A band due to Pb2+ ion in KBr crystal have been studied at 1.5K under various hydrostatic pressures up to 9.6kbar. The peak was observed to shift to high energy linearly with the pressure, while no change was observed in the line shape and intensity. Pb2+ ion is confirmed to occupy the on-center position at K+ lattice site. The absorption spectrum at normal pressure has also been studied at various temperatures between 15 and 380K, and the temperature shift of the A band is compared with the pressure shift

This paper reports the gas source MBE growth of new semiconductor TlInGaP and TlInGaAs layers on InP substrates and the observation of very low temperature-dependence of bandgap energy for these layers.

Self-organized quantum wire (QWR) structures are formed by the gas source molecular beam epitaxy growth of (GaP)/sub n/(InP)/sub m/ short period superlattices (n/m-SLs) on GaAs(011) substrate. Transmission electron microscopy observations show that the formed structures are elongated along the [011] direction with improved straightness and uniformity compared with those on GaAs(100). QWRs formed in (GaP)/sub n/(InP)/sub m/ SL/In/sub 0.49/Ga/sub 0.51/P multilayers (n/m-SL/InGaP MTLs) by self-organization exhibit a strong polarization dependence of the photoluminescence (PL) emission intensity for the fixed incident beam polarization. Temperature insensitive variation of the PL peak energy is also observed in these self-organized QWR structures.

(GaP) n (InP) n short-period superlattices (SLs) are grown on GaAs (N11) and (100) substrates by gas source molecular beam epitaxy. Transmission electron microscopy observations show that the SLs grown on GaAs (311)A and (411)A have lateral-composition-modulated dot/columnar structures with a lateral period of about 10–20 nm, while on GaAs (100), wire structures are formed. Photoluminescence (PL) peak energies are greatly dependent on substrate orientation and monolayer number n corresponding to the lateral composition modulation. On the other hand, the (GaP) n (InP) n SLs grown on GaAs (111) have no lateral composition modulation for n≤4 and have quasi-perfect CuPt-type ordering along the <111> growth direction for n=1, where the PL peak energy is 321 meV lower than that of disordered InGaP alloy. Quantum dots formed in (GaP)2(InP)2.5 SL/ In0.49Ga0.51P multilayers by self-organization exhibit strong 77 K PL with a full width at half-maximum of about 70 meV. Anomalous temperature variation of PL peak energy is observed in these self-organized structures.

GaN layers are grown on (0001) sapphire substrate by electron cyclotron resonance molecular beam epitaxy (ECR-MBE) using an ECR plasma cell with ion removal magnets on the cell top for the nitrogen source. The efficiency of the ion removal magnets in this ECR plasma cell is 99%. High-quality GaN layers are obtained. In particular, (2×2) and (4×4) RHEED (reflection high-energy electron diffraction) patterns are observed during GaN growth and during cooling after growth, respectively, indicating a flat and smooth surface of GaN. These results show the superiority of the ion-removed ECR plasma cell.

(GaP)(1)(InP)(1) superlattices (SLs) were grown on GaAs (100), (311), (411) and (111)B substrates by gas source MBE. Atomic force microscopy and transmission electron microscopy observations show that the SLs grown on GaAs (100), (311)A and (411)A substrates have wire, wire-like and dot-like lateral composition modulations, respectively. 4.2K photoluminescence peak energies are greatly dependent on the substrate orientation and growth temperature, ranging from 1.722 eV to 1.979 eV. The lowest peak energy ever reported, 273 meV lower than that of the disordered In0.5Ga0.5P alloy, is observed from the SL grown on GaAs (111)B substrate, where the strong CuPt-type ordering is confirmed.

Atomically controlled InGaAs/InP quantum well (QW) structures are grown on (001) InP substrates at 350 degrees C by gas source migration-enhanced epitaxy. Raman scattering measurement suggests the formation of tailored heterointerfaces: QWs having only InAs-type interfaces show the absence of Ga-P bonds, while QWs having InGaP-type interfaces indeed show the presence of Ga-P bonds. 4.2 K photoluminescence (PL) spectra for InGaAs/InP QWs show the very narrow line width comparable to the narrowest line width reported so far. PL peak energy variation with well thickness clearly depends on the heterointerface type, suggesting that the potential shifts to higher energies at the InGaP interfaces, while it drops at the InAs interfaces. Theoretical calculations assuming the formation of controlled heterointerfaces reproduce the experimentally observed PL energy variation.

We have newly developed multi-porous sheets fabricated from chemically polymerized polyaniline which are applicable for positive electrodes of ion rechargeable batteries. We have also developed novel multi-porous sheets for negative electrodes made of carbon material which are derived from synthetic organic polymer. Both sheets fabricated to have an area of maximum 1000cm2 and thickness of 0.3-3.0mm are reinforced by synthetic short fiber.Because of fiber-reinforcement, these sheets show excellent mechanical properties and easy handling in spite of their high porosity. The polyaniline positive electrodes have been combined with the carbon negative electrodes to produce high energy density cells having excellent cycle life and a high working voltage. Preliminary prototype CR 2016 cells made of these electrodes in welded steel can have demonstrated up to 17 mWh/cell.

The disordering and compositional change of the InGaAs/InP superlattice by the Ga ion beam was investigated, and using the effect, quantum wires were fabricated by focused Ga ion beam. The analysis of Raman scattering shows that in the implanted region intermixing, i.e., alloying takes place in such a way that the intermixed In1−xGaxAsyP1−y alloy has the compositions of alloy with the lattice constant nearly equal to that of InP, although at higher doses the compositions x and y become smaller due to larger interdiffusion. Focused Ga ion beam of 100 kV was irradiated in lines onto InP (350 Å)/InGaAs (50 Å)/InP (500 Å) single quantum well at doses of 1×1013 –1×1014 cm−2. Implanted samples were annealed at 650–670 °C for 60 min. The photoluminescence measurements at 30 K for wires with various widths show that with decreasing wire width the luminescence peak energy increases nearly following the change of the quantum levels in the potential well calculated by taking into account lateral straggling of implanted Ga ions. The implanted and alloyed regions are confirmed to act as potential barriers by which carriers are confined.

Optical studies of ultrathin Ge/Si superlattices grown on (001) Si substrates by phase-locked epitaxy have been carried out. The structures consist of alternating layers of pure Ge and Si with periods of 8, 10 and 12 monolayers. Using photo- and electroreflectance (PR and ER), four structurally induced optical transitions have been observed in the energy ragion 0.76–2.5 eV in both systems with periods of 8 and 10 monolayers. The transition energies show a blue shift with decreasing strain. At a growth temperature of 400°C, the PR and ER spectra of Ge6/Si6, which has a period of 12 monolayers, show not alloylike behavior but superlattice features similar to the samples with periods of 8 and 10 monolayers.

Pressure effects on F-center emission in KCl, KBr, KI, CsCl, CsBr, and CsI are observed under pressures ranging from 1 atm to 12 kbar at 1.6 K. In potassium halides the F-center emission shows a monotonic decrease with increasing pressure, while in cesium halides it shows an anomalous feature: It recovers and increases far beyond its value at 1 atm, after first decreasing at low pressures. These pressure effects observed at extremely low temperatures are considered to be due to dynamical nonradiative transitions, and can be explained by the Dexter-Klick-Russell mechanism in a one-dimensional configuration coordinate model under hydrostatic pressure.

An apparatus has been developed which permits optical measurements up to 30 kbar at 1.5K using a piston-cylinder-type high-pressure cell. Using this apparatus, studies of the hydrostatic pressure effects of absorption spectra of KI and KBr doped with Tl+ or In+ have been made up to 10 kbar. Under high pressure, a mutual mixing occurs due to the electron-lattice interaction between the excited states corresponding to the A, B, C and D absorption bands, even at low temperatures, resulting in the give-and-take of the absorption intensity between these absorption bands. To explain the mutual mixing, the pressure dependence of the electron-lattice coupling is taken into account. The pressure variation of the A band shape is also discussed in connection with the pressure dependence of the electron-lattice coupling constants.

AbstractThe assignment of the absorption bands in cesium halide thallous phosphors (CsI:Tl and CsBr:Tl) is performed by making use of the phase transition from NaCl‐type to CsCl‐type under high pressures. It is concluded that the longest wavelength band corresponds to the A band in alkali halide thallous system and the origin of the next wavelength one is the A‐like transition, that is, the transition to the excited state similar to that in the case of the A band which has two relaxed excited states.

The known and new bands of the luminescence in NaBr:Cu+ are observed under different pressures at low temperatures. The pressure dependence of the lifetimes of these bands is measured with one of NaCl:Cu+, and the position of the Cu+ ion in relaxed excited state (RES) is discussed with these experimental results.