Hirofumi Mino

Influence of excitation power and temperature on photoluminescence in InGaN/GaN multiple quantum wells.

Excitation power and temperature dependences of the photoluminescence (PL) spectra are studied in InGaN/GaN multiple quantum wells (MQWs). The excitation power dependences of the PL peak energy and linewidth indicate that the emission process of the MQWs is dominated first by the Coulomb screening effect and then by the localized states filling at low temperature, and that the nonradiative centers are thermally activated in low excitation range at room temperature. The anomalous temperature dependences of the peak energy and linewidth are well explained by the localized carrier hopping and thermalization process, and by the exponentially increased density of states with energy in the band tail. Moreover, it is also found that internal quantum efficiency is related to the mechanism conversion from nonradiative to radiative mechanism, and up to the carriers escaping from localized states.

Optically induced long-lived electron spin coherence in ZnSe∕BeTe type-II quantum wells

The spin coherence of photoexcited electrons in ZnSe∕BeTe type-II quantum wells has been investigated by the time-resolved Kerr rotation technique. Fast and efficient escape of photoexcited holes from the ZnSe layers to the BeTe layers suppresses the electron-hole recombination and their exchange interaction. This effect leads to the formation of dense electrons in ZnSe layers and long electron spin dephasing time reaching a value of 6.1ns at 1.4K.

Biexciton spin states of diluted magnetic semiconductor quantum wells in high magnetic fields

An exciton and a biexciton photoluminescence in (Cd,Mn)Te/CdTe/(Cd,Mg)Te asymmetric quantum wells were investigated under magnetic fields. A quantum beat between an exciton and a biexciton has been observed by a transient four-wave-mixing spectroscopy. The spin-energy structures have been clarified by spectra of the four-wave-mixing signals. We have observed decrease of the intensity ratio of a biexciton to an exciton on increasing magnetic field. The instability of the spin singlet biexciton state is determined by the inner effective magnetic field produced by the local Mn magnetic moments.

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.

Dresselhaus field-induced anisotropic spin propagation in ZnSe/BeTe type-II quantum wells

The dynamics of photo-injected electrons and the propagation of photo-created spins in nondoped ZnSe/BeTe type-II quantum wells were investigated by time-resolved photo-induced circular dichroism microscopy at room temperature. Spin propagation from the pump spot presents a directionally dependent spin precession frequency in a magnetic field in Voigt configuration. This anisotropic spin propagation is ascribed to the Dresselhaus effect (G. Dresselhaus, Phys. Rev. 100, 580, 1955) on the radially diffusing photo-injected electrons, since the anisotropy depends on both the directions of crystallographic axis and magnetic field.

Electric- and magnetic-field effects on radiative recombination in modulation n-doped ZnSe/BeTe type-II quantum wells

We have studied the photoluminescence properties of modulation n-doped ZnSe/BeTe/ZnSe type-II quantum wells. The luminescence spectra and the polarization anisotropy depend strikingly on both the n-doping into the barrier layers and an applied external electric field perpendicular to the layers. These are explained by screening of a built-in electric field with n-doping and Stark effects due to the applied electric field. We find optical Shubinkov–de Hass oscillations in both the photoluminescence intensity and the transition energy under a high magnetic field perpendicular to the well. These features and additional infrared cyclotron-resonance measurements demonstrate that two-dimensional electron gas of a high concentration has been formed in the doped samples. All these present the signature of the charged excitons and also of a correlated excitonic phase of type-II quantum wells.

Optical de Haas oscillations of charged excitons in type-II ZnSe/BeTe quantum wells

We have studied the optical properties of the modulation n-doped ZnSe/BeTe/ZnSe type-II quantum wells. The reflection spectra have shown typical negatively charged exciton features only in a doped sample. The electron density as well as the mass was determined in high magnetic field (up to 160 T) cyclotron-resonance measurements. Photoluminescence (PL) measurements were performed in pulsed high magnetic fields (up to 42 T) with a Faraday configuration. We found oscillations in both the PL intensity and the peak energy in the doped sample. These oscillations were originated from optical de Haas oscillations. It was found that the observed indirect PL transition occurs via the charged excitons in a type-II quantum configuration.

Spatially direct charged exciton photoluminescence in undoped ZnSe∕BeTe type-II quantum wells

Photoluminescence (PL) spectra occurred as a spatially direct optical transition inside of the ZnSe layer in undoped ZnSe∕BeTe∕ZnSe type-II quantum structures have been studied. We have found that the charged exciton transition was observed at the lower energy side of the exciton transition in the spatially direct PL. The formation of the charged exciton was attributed to the accumulated electrons in the ZnSe layer after the photoexcitation accompanied by the holes being escaped from this well and injected into the BeTe layer.

Bright photoemission from interacting excitons at the interface localized sites in CdS/ZnSe type‐II quantum structures

We investigated the bright photoluminescence (PL) of CdS/ZnSe type‐II quantum structures in which the lateral potential fluctuation plays an important role on the dynamics of carriers due to their long lifetime. The temperature dependence of PL energy showed the typical “s” ‐like shape with increasing temperature and Monte Carlo simulation well reproduced the experimental results qualitatively and quantitatively. The exponential distribution of localization energy for excitons was supposed by the simulation. We conclude that the bright PL originates in the recombination of localized interacting excitons gathered at a local potential minimum.

Magneto-Optical Four-Wave-Mixing Studies of an Exciton–Biexciton System in a CdMnTe/CdTe/CdMgTe Single Quantum Well

Exciton and biexciton states in a CdMnTe/CdTe/CdMgTe quantum well were investigated by means of polarization-dependent four-wave mixing (FWM) measurements in magnetic fields up to 7 T. In co-linear...