Optical Nonlinearity in CdSSe Microcrystallites Embedded in Glasses(Advanced Nano Technologies,<Special Section>Microoptomechatronics)

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概要

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• We investigate the enhancement of the optical nonlinearity and the limit of the improvement of the response speed in CdS_xSe_<1-x> microcrystallites by measuring the effective optical nonlinear cross section (σ_<eff>), the energy decay time (T_1) and the dephasing time in two kinds of semiconductor microcrystallites of CdS_<0.12>Se_<0.8> microcrystallites embedded in alkaline multi-component glasses (CdSSeMs) and CdSe microcrystallites embedded in SiO_2 thin film (CdSeMs). As the average radius of CdSSeMs decreases from 10 to 1nm, the values of σ_<eff> and T_1 gradually change from 2.6×10^<-16> to 1.1×10^<-16>cm^2 and from dozens picoseconds to 4psec, respectively. The size dependence of CdSSEMs shows that the energy level structure in the microcrystallite with a radius of less than a few nanometers is a two-level system, in which σ_<eff> is proportional to T_2. The carrier recombination time (τ) of CdSSeMs with the average radius of 1nm is estimated to 2psec. As the average radius of a CdS_<0.12>Se_<0.8> microcrystallite decreases from 9 to 3nm, the values of T_2 gradually change from 640 to 230fsec at 18K, respectively. The size and temperature dependences of T_2 for the CdSSeMs show that there is the discrepancy between the theory and the measured T_2. The discrepancy showes the presence of the acoustic-phonon-assisted relaxation processes other than the puredephasing processes. It is indicated that T_2 becomes long by reducing the excessive acoustic-phonon-assisted relaxation processes, and that the longer T_2 might enhance σ_<eff>. We investigate the enhancement of σ_<eff> in CdSeMs by making T_2 longer. The τ, σ_<eff>, and T_2 of CdSeM an average radius of 3nm are 40psec, 4.5×10^<-15>cm^2, and 150fsec at room temperature. The σ_<eff> is ten times as large as that of CdSSeM sample at the same average radius and the enhancement of σ_<eff> can be considered to be caused by the longer T_2.

• 2007-01-01

著者

• Shinojima Hiroyuki

  Ntt Mi Labs Ntt Corporation

• Shinojima Hiroyuki

  Ntt Microsystem Integration Laboratories Ntt Corporation

• Shinojima Hiroyuki

  NTT MI Laboratories, 27-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan

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