Yoshihiro Takiguchi

Dynamic effect of weak localization on the light scattering from random media using ultrafast laser technology

Angle and time resolved experiments on the backscattering of light from model random media are presented. Weak localization was observed using 30-fs laser pulses, where this time scale is shorter than the scattering mean free time of the light in the random medium. This observation implies that the coherent peak is due to interference between the scattered light at the point of observation. The time resolved experiment directly shows that the light rays which undergo longer scattering paths contribute to the narrow coherent peak. A proper description of the temporal profile pulses scattered from random media requires the effect of weak localization to be taken into account.

Piezospectroscopy of GaAs and GaAs/GaAlAs single quantum wells grown on (001) Si substrates

The effects of large external stress (S) along [100] on the optical features associated with biaxially strained bulk GaAs and two GaAs/GaAlAs single quantum wells (SQWs) grown on (001) Si have been observed using photoreflectance at 300 K. This stress configuration makes it possible to externally alter the light (LH)‐ and heavy (HH)‐hole splitting in both the bulk material and the SQWs. In a SQW of width 200 A, the ground state was continuously tuned from LH to HH. In the bulk material, a stress‐induced anticrossing of the LH and HH features of the fundamental gap was determined with an interesting polarization effect.

Photoreflectance study of GaAs and GaAs/GaAlAs single quantum wells grown on (001) Si substrates

Abstract The optical features associated with biaxially strained bulk GaAs and three GaAs/GaAlAs quantum wells (QWs), with widths of 52 A, 120 A and 200 A, grown on (001) Si have been studied using photoreflectance at 300 K and 77 K. The ordering and/or separation of the light- and heavy-hole quantum transitions in the QWs can be tuned by altering the width of the well.

Effects of uniaxial stress on the optical properties of GaAs and GaAs/Ga1−xAl1−x As single quantum wells grown on Si(001) substrates

Abstract The effects of a large external uniaxial stress ([sgrave]) along [100] on the optical features associated with biaxially strained bulk GaAs and two GaAs/Ga1−xAl x As single quantum wells (SQWs), with widths of 52 and 200 A, grown on Si(001) have been studied using photoreflectance at 77 and 300 K. Measurements were made with incident light polarized parallel and perpendicular to [sgrave]. This stress configuration makes it possible to externally alter the light-hole (LH) and heavy-hole (HH) splitting in both the bulk material and the SQWs. In the SQW of width 200 A, the ground-state valence band was continually tuned from HLs to HHs. In the bulk material, a stress-induced anticrossing of the LH and HH features of the fundamental gap was observed with an interesting polarization effect.

Exciton trapping in strained GaAsP quantum wells

Exciton trapping time to interface islands in GaAsP/AlGaAs strained quantum wells is found to be of the order of 30 ps.

Exciton dynamics in 121A GaAs and GaAsP QWs having different valence band structures arising from built-in biaxial stress

Exciton dynamics in various 121 angstroms single quantum wells (QWs): a AlGaAs/GaAs QW and two AlGaAs/GaAsP QWs, under different built-in biaxial tension, has been investigated using time resolved photoluminescence (PL) spectroscopy at 5 K. Heavy-hole (hh) and light-hole (lh) exciton formation times from free electron-hole pair, hh (lh) exciton to lh (hh) exciton inter-subband relaxation times, exciton localization times to interface islands, and localized exciton annihilation decay times in the strained and non-strained QWs have been determined by fitting the PL time profiles at the lowest emission energy with an analytical solution for the localized exciton population profile obtained by solving six level rate equations.

Electron energy relaxation dynamics in GaAs quantum wells grown on Si: cool-hole effect

Cool hole effect on hot electron energy relaxation dynamics in GaAs quantum wells grown on Si was investigated using photoreflectance and time-resolved photoluminescence spectroscopies. It was demonstrated that for the quantum wells in which there is a two- dimensional light (heavy) mass hole gas the electron energy relaxation is dominated by electron-hole (electron-longitudinal optical phonon) energy exchange.

Hot carrier dynamics in GaAs epilayer structures grown on Si

Picosecond time- and energy-resolved photoluminescence (PL) spectroscopy is used to investigate hot carrier dynamics in GaAs epilayer structures grown on silicon substrates. The existence of biaxial stress arising from the thermal expansion difference between GaAs and Si substrates alters the valence band of GaAs epilayer structures on Si. Using the radiative transitions from electrons in donor (Si, 1016 cm-3) states to separated valence bands in a 2 mu m GaAs epilayer on Si, energy relaxation of thermalized hot holes is studied. Different electron energy relaxation dynamics are observed in thin and wide modulation Be-doped GaAs-AlGaAs multiple quantum wells grown on Si substrates, arising from different valence subband structures.

Picosecond Γ-X carrier in GaAs/AlAs superlattice

(Gamma) -X carrier scattering in 35 angstroms/35 angstroms GaAs/AlAs superlattice at 5 K was investigated using time-resolved photoluminescence spectroscopy.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Energy relaxation of hot holes in GaAs grown on Si

I-lot hole energy relaxation dynamics are reported using time- and energy-resolved photoluminescence spectroscopy. The hole cooling rate is determined to be smaller than expected bed on hole scatterings with longitudinal optical phonons.