Shin'ichi Katayama

Photoluminescence and Raman spectra of ZnO thin films by charged liquid cluster beam technique

Zinc oxide (ZnO) thin films have been deposited on glass substrates from isopropyl solutions of zinc acetate by using the Charged Liquid Cluster Beam (CLCB) technique. The structure of the films is determined by the temperature of the substrate. Raman scattering spectra of the films obtained by non-resonant excitation are similar to those of bulk polycrystalline ZnO. The photoluminescence (PL) spectra of the films exhibit at 10 K four broad emission bands in the visible and near infrared spectral range. The effect of post-deposition annealing on the red emission band is also reported.

Magnetic oscillation of luminescence energy in modulation-doped quantum wells

Abstract Photoluminescence energy in strong magnetic fields is explored theoretically by taking into account many-body electron-electron and electron-hole interactions in modulation-doped GaAs/AlGaAs quantum wells. With use of the plasmon-pole approximation for dielectric function, we find the clear magnetic oscillation of the self-energy of a photo-excited hole in the lowest Landau level. The corresponding shift for electrons is nearly independent of the magnetic field. The calculation explains well the oscillatory behavior of luminescence energy observed experimentally.

Ferroelectric phase transition in monoclinic TlS

Abstract The dielectric property of newly found monoclinic thallium monosulfide (TlS) has been investigated in the temperature range from 285 to 380 K. The dielectric constants show anomalous increases at 3186 and 341.1 K suggesting the occurrence of successive phase transitions. A study of the polarization hysteresis loop shows that this compound is ferroelectric in the room temperature phase. The nature of the phase transitions is probed by calorimetric and X-ray measurements.

Analysis of Raman Spectra from Heavily Doped p -GaAs

A theory of Raman scattering by both coupled LO phonon-plasmon (LO-PL) modes and surface “unscreened” LO phonons in a doped semiconductor is presented with a simple two-layer (surface depletion layer-bulk substrate) model. Effects of the optical penetration depth and the depletion layer thickness on the line shape are examined. The theory is applied to an analysis of Raman spectra from a (100) surface of p -GaAs, and reproduces experimental profiles very well. An analysis suggests that the observed broad band near the transverse optical phonon frequency is ascribed to the lower branch of the coupled LO-PL modes.

Theory of energy relaxation of 2D hot carriers in GaAs quantum wells

Abstract The energy relaxation rate of two-dimensional (2D) hot carriers due to LO phonon emission is explored theoretically by assuming a simple quantum-well structure for GaAsAl x Ga 1− x As superlattices. The differences of energy loss rate between electrons and holes are shown with emphasis on the roles of free carrier screening and form factors. The picosecond cooling behavior of photoexcited 2D carriers is presented on the basis of the polar carrier-LO phonon coupling process.

Magnetic Oscillation of Luminescence Energy in Single Heterostructures

Magnetic-field dependence of luminescence energy due to recombination of a two-dimensional electron and a photo-excited hole trapped in an acceptor state in n-type GaAs/AlGaAs single hetero-structures is calculated. The luminescence energy shows red shift when the Fermi energy is in an energy gap between adjacent Landau levels. Amplitude of the red shift decreases as the distance between acceptors and the hetero-interface increases. When the distance is larger than a few hundred angstroms, the energy oscillation of electrons becomes dominant. Calculated first moment (center of gravity) of luminescence spectrum reproduces result of a recent experiment quite well.

Successive structural phase transitions in monoclinic thallium monosulphide

The structural phase transitions in newly found monoclinic TlS have been studied using single-crystal X-ray diffraction methods. The room temperature ferroelectric phase has a commensurate structure; the satellite reflections are observed at qc=(0, 0, 1/4) suggesting fourfold lattice modulations along the c axis. The intermediate phase between 318.6 K and 341.1 K is incommensurate; the satellites shift from qc to qi=(0.04, 0, 1/4). In the high-temperature paraelectric phase above 341.1 K, these satellite reflections disappear. A phenomenological treatment of the successive phase transitions in TlS is given. The temperature dependence of the dielectric constant is also discussed. The experimental results are compared with those for TlGaSe2.

Photo-irradiation effect on dynamics of charge-density-wave condensate in quasi-one-dimensional conductors TaS3

Abstract We find a new photo-irradiation effect on the current–voltage characteristics of quasi-one-dimensional conductors TaS3. When the TaS3 single crystal is irradiated with a weak 488 nm emission from Ar+ laser, the electrical current is enhanced around the threshold voltage Vt below the Peierls transition temperature TP. The current enhancement is attributed to the increase of charge-density-wave (CDW) contribution due to the screened pinning potentials by photo-excited quasi-particles in plastic creep phase of CDW motion.

Field modulation effects on charge-density-wave conduction in NbSe3

Abstract Characteristics of charge-density-wave field-effect transistors (CDW FETs) with NbSe 3 channel layer were investigated. Contrary to previous investigations, we have found that the change of the drain current is symmetric for sign reversal of the gate voltage for samples of good quality. Measuring samples with different gate length, we have confirmed that the current modulation takes place under the gate electrode. The current modulation in the high-temperature CDW phase has been confirmed.

Far-infrared emission spectra from hot two-dimensional plasma in heterojunctions

Abstract A theory of grating-coupler-induced light emission from nonradiative two-dimensional plasmon modes in single heterostructures is presented. The theory is evaluated by a model calculation of emission spectra assuming Al x Ga 1− x As/GaAs single heterojunctions with a metallic (or dielectric) grating. It is shown that emission spectra depend strongly on the dielectric property of the layered structures modulated by the surface grating as well as the sheet conductivity of the grating.