Results of our photoluminescence measurements on high quality ZnSe single crystals and doped crystals are described. Discussions are given to emissions related to free excitons, donor bound excitons and their excited states. The origin of D-A pair emissions related to doped Li and Na is clarified and Cu dope experiments reveal a possibility of site control of Cu from interstitial to substitutional sites. A emission of free excitons scattered by electrons is found in the twined crystals.

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Te-doped ZnS crystals were prepared by solution growth using Sb-Te or Sb₂Te₃-Sb₂S₃ as solvent. The grown crystals showed the blue emission bands due to the Te_l and Te₂ isoelectronic traps. As the Te concentration in the grown crystal increased, the relative intensity of the Te₂ band to the Te_l increased. Vacuum fluorescent display using the grown ZnS: Te crystals as a phosphor emitted the blue light peaking at 460nm.
Te-doped ZnS_1-xSe_x crystals were grown from ZnSe-ZnSe-Sb₂S₃-Sb₂Se₃-Sb₂Te₃ solutions. The Se composition x in the grown crystal was varied through the fraction [Se]/([S]+[Se]) in the starting materials. The Te concentration in the grown crystal depended on the fraction [Te]/([S]+[Se]+[Te]) in the starting materials. The grown crystals showed the emission band due to Te₁ and Te₂. As the Se composition x increased, the peak position decreased and the band width became narrow for the Te₁ band. We believe that this tendency is available to improve the color purity of the luminescence from the phosphor.

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We developed photoassisted MBE of ZnSe on GaAs (100) substrates using a He-Cd laser (441.6nm). The epilayer thicknesses were reduced by the irradiation during growth and also after growth. Photodesorption rate constant of adatoms were obtained and it was clarified that these photodesorption were photo-enhanced thermal desorption. The desorption was enhanced totally under the coexistence of the photogenerated electrons and holes at the epilayer surface. Adsorption and desorption processes of Zn and Se adatoms on the ZnSe (100) surface were also investigated by RHEED. Chopped irradiation was used during growth and it was revealed that the effects persisted about 5 ms after the light was turned off.
Reduction in the density of hillocks, extension of the critical thickness, increase in the intensities of free-exciton emissions and lowering of the epitaxial temperature (150°C) were realized by photoassisted MBE. These improvements due to the irradiation can be explained by the migration enhancement of surface adatoms by the irradiation. Light irradiation effects on doping of impurities were investigated. A model of selective transfer of photogenerated carriers is proposed and the behavior of surface adatoms is discussed.

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We report low temperature growth of zinc chalcogenides (ZnS and ZnSe) on GaAs by the technique proposed by our group which is to use high velocity molecular beams, i. e., the atoms or molecules supplied themselves have the energy necessary for migration on the growing surface. New type of effusion cells to obtain high velocity beams are described in detail. This technique is successfully used for the growth of ZnSe and ZnS at temperatures less than 200°C. The epitaxial growth were confirmed by observing RHEED pattern. The observed RHEED patterns, especially of chevron or arrowhead ones for ZnS are discussed on the basis of lattice relaxation between the substrate and the epilayer. It has been confirmed by low temperature photoluminescence measurements that high quality epilayers are grown by this method. Secondary ion mass spectroscopy showed the existense of large amount of Ga atoms near the hetero-interface both for ZnS/GaAs and ZnSe/GaAs. The origin of Ga is discussed on the Ga droplets formed on GaAs surface during the thermal cleaning.

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Exciton lines and Raman scattering lines appearing at band edge region of epitaxial ZnS films were investigated under tunable picosecond light pulse excitations. The decay times of excitons bound to neutral donors (I₂ line) and acceptors (I₁ line) at low temperatures were measured for the first time with the use of a streak camera. The decay times of the I₁ and I₂ lines were found to be -190 ps and 40-60 ps, respectively. These decay times were compared with calculations based on the giant oscillator strength model and Sanders-Chang's theory. Under tunable (3.7-3.9eV) picosecond light pulse excitations, resonant enhancements of Raman scattering intensities were observed for LO-, 2LO-, 3LO-, TO- and LO+TO-phonon lines. The dependence of two LO-phonon Raman line intensity on excitation photon energy showed resonant enhancements with the free exciton state.

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We have investigated the phenomenon of layer disordering in CdZnSe/ZnSe strained layer superlattices by Ge-diffusion and have fabricated CdZnSe/ZnSe optical waveguides using the Ge-induced disordering. Lateral optical confinement in stripe geometry laser was confirmed by observing the near field distribution of guided wave. We also report the first confirmation of disordering of CdZnSe/ZnSe strained layer superlattices by ionimplantation and low temperature annealing. We confirmed that superlattice structure was disordered by Si ion implantation and subsequent annealing at 300°C.

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By using a hot-wall epitaxy method, we have prepared Zn_l-xCd_xSe/ZnSe (x=0.2-0.3) superlattices with the well width of 15-69Å and the barrier width of 40-120 Å. Stimulated emission processes have been studied under high optical excitation intensities in temperature range between 25K and 300K. We find that the exciton-exciton scattering effect is significant in the stimulated emission process. As the exciton density is increased above the Mott transition density, an emission due to the recombination of electron-hole plasmas appears and dominates the emission spectra at room temperature. Stimulated emissions by the phace space filling effect of the excitons have also been measured in the single quantum well structure.

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Strain induced band offsets of the conduction band and valence subbands in Cd_xZn_lxS/ZnS superlattices have theoretically been calculated on the basis of the modelsolid theory taking into account of spinorbit energy(Δ_so). The conduction and valence band offsets have been estimated as a function of the well layer thickness and Cd composition (x), and as a result the valence band offsets which are derived from heavy hole and light hole bands increase with both decreasing the well layer thickness and Zn composition. Effect of external uniaxial compressive stress (ε) on the band offsets indicates that the energy difference between the heavy hole band in CdZnS well and the light hole band in ZnS barrier increases monotonously with applied stress. On the other hand, that of light hole bands shows a quadratic energy shift as a function of uniaxial stress and has a minimum energy value around ε/Δ_so. It is pointed out that a large energy difference in uniaxial deformation potential constants between CdS and ZnS shows a unique behaviour which significantly modifies the electronic states in the CdZnS based quantum well structures under uniaxial stress.

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In this paper, we propose two superlattice structures as pseudo-quaternary ZnCdSSe layers. They consist of three layers or four layers in a cycle with three kinds of binary compound materials, i.e., ZnS, ZnSe and CdS. In order to estimate the equilibrium in-plane lattice constant of these layers, a general expression for superlattices consisting of n (n=2, 3, 4, …) layers in a cycle has been derived by minimizing the total elastic strain energy. The effective bandgap for the superlattices with different combinations of the layer thickness in a cycle were calculated using Kronig-Penney model, where the strain effect was taken into account in calculating the bandgap and the band offset. The calculated results of the effective bandgaps were compared with the bandgap of ZnCdSSe quaternary alloy.

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In this paper, an LC Simulation-Type RC active filter with all-pole low-pass characteristics is presented. The proposed circuit simulates the doubly terminated ladder filters realized by lossy inductors and negatively lossy capacitors. First, an LC filter with lossy LC elements is proposed as a filter to be simulated. Second, an RC active filter which simulates the LCR filter with a reduced number of voltage followers and NIC's is proposed. Finally, a fifth-order Chebyshev low-pass filter is designed, the measured transfer response is in a good agreement with the theoretical value and it is shown that the sensitivity of the proposed circuit is much lower than that of the circuit by cascading Sallen-Key circuits.

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Response chracteristics of the electronic excitable membrane model by Tsukada, et al. to perodic pulse stimuli are investigated. Use of phase plane analysis and of phase transition curve extended by Maginu is made in order to clarify the characteristics. Relationship between the response characteristics (the shape of the phase transition curve) and the circuit parameters (values of the resistors, capacitors and voltage source) of the model is also discussed. The mean firing rate shows a shape of devil's staircase as reported in many literatures when the pulse intensity or the period of the stimuli changes. Parameter values of the model can be set so as to mimic a real excitable membrane as far as the mean firing rate is concerned.

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It is difficult to obtain the optimal solution to combinatorial problems. The more the number of variables increases, the more calculation time explosively increase. Therefore approximation methods are needed to the kind of problems. Traveling Salesman Problem (TSP) is one of typical combinatorial problems. Using geometric information, this problem can be solved effectively. It is difficult however to use the information on the basis of almost all approximation method. It is shown that the information can be used effectively in Case -Based Reasoning (CBR) system to TSP.
In this paper, we make a system based on CBR for TSP and present a new retrieval method to find the most similar case for the problem. In addition, by dividing a large combinational problem into sub-problems and applying the system to each sub-problem, an approximation solution to a large combinational problem can be obtained in ten or so minutes.

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Over the past few years, a considerable number of studies have been done on help systems, which support users by effectively presenting information necessary to use the application software. However, most of studies have the following problems:
(1) It is difficult to deal with context-dependent knowledge.
(2) If a help system fails recognition of user intention, incorrect processing in the help system is carried out.
This paper proposes an intelligent help system to realize a smooth communication between a user and an application software by repeating recognition of the user intention and visualization of system's status. The proposed help system consists of the following parts:
(i) the input part that gets user words.
(ii) the intention-recognition part that recognizes the user intention from the user words.
(iii) the visualization part that intuitively visualizes the user intention and corresponding operation method of the application system to the users.
This paper applies the intelligent help system to the drawing tool and shows that the intelligent help system resolves the above problems. The intelligent help system recognizes user intention when user words are given and visualizes the user intention and the corresponding operation method even if the user does not know the operation method desired to realize one's intention.

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