Takuma Tsuchiya

Magnetic Oscillation of Luminescence Energy in Asymmetric Quantum Wells

Magnetic-field dependence of luminescence energy due to recombination of a two-dimensional electron and a photogenerated free hole in one-side-doped n-type GaAs/AlGaAs single quantum wells is calculated. The luminescence energy shows an anomalous shift when the Fermi energy is in an energy gap between adjacent Landau levels. The direction of this energy shift depends on the well width. This is due to well-width dependence of screening strength of two-dimensional electron gas for holes.

Biexcitons and charged excitons in quantum dots: a quantum Monte Carlo study

Abstract Binding energies of biexcitons and positively and negatively charged excitons in CuCl/NaCl and GaAs/Al 0.3 Ga 0.7 As spherical quantum dots were calculated exactly by the diffusion Monte Carlo method. We have found that binding energy for negatively charged excitons can be larger than that of biexcitons. For small GaAs dots, binding energies of biexcitons and positively charged excitons become negative, because of the difference of quantum confinement between electrons and holes. For quantum dot whose radius is much larger than the effective Bohr radius, the binding energies are reproduced quite well by a simple expression.

A fully operational 1-kbit HEMT static RAM

In this paper we describe the current status of materials and fabrication technologies, and optimal design of a memory cell, and the performance of fully functional 1-kbit HEMT SRAMs. The surface defect density on MBE-grown wafers has been reduced to less than 100 cm-2by improving MBE technology. Standard deviations of threshold voltages are 6.7 and 11.8 mV for enhancement-type and depletion-type HEMTs, respectively, measured in a 10 mm × 10 mm area. These deviations are sufficiently small for DCFL circuits. Memory cell design parameters have been optimized by circuit simulation, where the effects of variations in threshold voltages are taken into account. Full function of 1-kbit SRAMs has been confirmed by marching tests and partial galloping tests. The RAM chips have also shown excellent uniformity in access time. The difference between maximum and average values on the RAM chip is 4 percent.

Dynamical spin properties of exciton and biexciton in CdMnTe/CdTe/CdMgTe single quantum well

Abstract Exciton and biexciton optical properties in II–VI semiconductor single quantum well have been studied by magneto-photoluminescence, and time-resolved four-wave-mixing spectroscopies. The polarization dependence of both measurements can clearly distinguish biexciton from other bound states and show the dynamical spin properties of exciton and biexciton.

Biexcitons and charged excitons in GaAs/AlAs type-II superlattices: a quantum Monte Carlo study

Biexcitons and positively and negatively charged excitons in GaAs/AlAs short-period type-II superlattices have been investigated by the diffusion Monte Carlo method. As opposed to the bulk and type-I quantum wells, we found that binding energies for charged excitons are much larger than those of biexcitons. This is explained by inter-particle configuration peculiar to type-II superlattices.

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.

A quantum Monte Carlo study on excitonic molecules in type-II superlattices

Abstract Binding energy of excitonic molecules in short-period (GaAs)n(AlAs)n type-II superlattices is calculated exactly by the diffusion Monte Carlo method in the effective mass approximation. For n=8–13, calculated binding energy increases monotonically with decreasing well width, but the ratio between the binding energy of an excitonic molecule and that of an exciton is about 0.15 and independent of layer width. Rough estimation of inter-particle distance shows that two holes are in the same GaAs layer and are sandwiched between two electrons in AlAs layers in the ground state.

A QUANTUM MONTE CARLO STUDY ON EXCITONIC COMPLEXES IN GaAs/AlGaAs QUANTUM WIRES

Binding energies of biexcitons and charged excitons in GaAs/Al0.3Ga0.7As quantum wires were calculated by the diffusion Monte Carlo method. The binding energy for the negatively charged excitons is enhanced strongly, because of the mismatch of the electron and the hole wave functions. The resulting biexciton binding energy reproduces experimental results quite well.

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.

Phase of magnetic oscillation of luminescence energy in asymmetric quantum wells

The energy of photoluminescence due to recombination of a photogenerated free hole and a two-dimensional electron is calculated in an n-type GaAs/AlGaAs asymmetric single quantum well in high magnetic fields. The magnetic oscillation undergoes a phase change at a certain strength of applied electric field because of the change in the strength of the electron-hole interaction.