Modification of two-photon excited fluorescence from quantum dots on SiN photonic crystals

We investigate two-photon excited fluorescence from CdSe quantum dots with a center-emitting wavelength of 655 nm on SiN photonic crystals. We find that two-photon excited fluorescence is enhanced by more than 1 order of magnitude in the vertical direction when a photonic crystal is used compared to the fluorescence spectra in the absence of photonic crystals. The spectrum of two-photon excited fluorescence from quantum dots on SiN photonic crystal is observed to shift to blue compared to that from quantum dots on SiN without photonic crystals. (C) 2010 Optical Society of America

Dynamics of spontaneous emission from SiN with two-dimensional photonic crystals

We investigated the dynamics of spontaneous emission from a photonic crystal etched into a SiN slab. After fitting the decay curves of the emission to double exponential functions, we divided the dynamic process of the spontaneous emission into a fast process and a slow process. It was observed that the presence of the photonic crystal increased the proportion of the fast decay component, and consequently, the emission rate and time-integrated emission intensity were also enhanced. These enhancements were a result of the coupling of the guide modes to the leaky modes of the photonic crystal slab waveguide. (C) 2008 Optical Society of America.

Two-photon excited fluorescence from CdSe quantum dots on SiN photonic crystals

Two-photon excited fluorescence from CdSe quantum dots on a two-dimensional SiN photonic crystal surface is investigated by using a femtosecond laser. By using a photonic crystal, a 90-fold enhancement in the two-photon excited fluorescence in the vertical direction is achieved. This is the highest enhancement achieved so far in the two-photon excited fluorescence in the vertical direction. The mechanism of the enhancement for two-photon excited fluorescence from quantum dots on photonic crystals is analyzed.

Fourier transformation study of the Franz-Keldysh Oscillation in SIN+ GaAs structures

Fourier transformation (FT) method has been used in the theoretical lineshape analysis of the Franz-Keldysh Oscillation (FKO) in detail by numerical simulation. The FKO of a set of GaAs SIN+ samples was obtained in photoreflectance measurements. The FT spectra of a part of the samples,including of the real part,imaginary part, and mode of the FT,are well consistent with the theoretical lineshapes. The ratio of the square root of the reduced mass of the light hole (LH) to the heavy hole (HH), root mu(1)/root mu(h), obtained in the analysis was in the range of 0.805 to 0.816 for different samples. In addition,the built-in electric field F-1, and the modulation field delta F = F-1 - F-2 induced by photo-modulation were also obtained in the analysis. However,for a few samples great difference was found in the lineshape of the real part and imaginary part of their FT spectra from the theoretical lineshape. In this case the mode of the FT spectra still can be used to obtain useful information.

ENHANCEMENT EFFECT OF PLASMA-ENHANCED CHEMICAL-VAPOR-DEPOSITED SIN CAPPING LAYER ON DIELECTRIC CAP QUANTUM-WELL DISORDERING

Quantum well disordering of GaAs/AlGaAs multiple quantum well(MQW) has been accomplished with only plasma enhanced chemical vapor deposited (PECVD) SiN cap layer growth. The amount of blue shift increases with SiN growing time. This result has been explained by the vacancy indiffusion during PECVD SiN growth. Rapid thermal annealing (RTA) of the sample after SiN cap layer growth at 850 degrees C for 35 s caused a larger amount of blue shift than those obtained without RTA. By considering the model of Al diffusion from AlGaAs barrier into GaAs QWs together with the result from photoluminescence (PL) measurement, Al diffusion coefficients were calculated. The Al diffusion coefficient due to PECVD SiN was estimated at about 3 x10(-17) cm(2)/s. It was possible to extract the effect of RTA on the QW disordering, which showed that the amount of the blue shift and the Al diffusion coefficient due only to RTA increases with SiN cap layer thickness as reported by Chi et al.(10))

SiN薄膜三阶非线性增强的研究

采用射频磁控反应溅射法结合热退火处理技术制备纳米硅镶嵌氮化硅(ncSi-SiN_x)复合薄膜.通过X射线能谱(EDS)、X射线衍射仪(XRD)的测定,对薄膜进行了结构及所包含硅晶粒大小的表征.采用皮秒激光器运用单光束Z扫描技术开展了对该复合薄膜的非线性光学性质的研究,测得其三阶非线性折射率系数和非线性光吸收系数分别为10~(-8) esu和10~(-8)m/W量级,并将薄膜这种三阶光学非线性的增强归因于量子限域效应.

SIN~+GaAs结构中的Franz-Keldysh振荡的傅里叶变换研究

利用傅里叶变换(FT)方法，对Franz-Keldysh振荡(FKO)的理论线性作了详细的数值模拟，并用光调制反射谱(PR)测量了一组本征层(I层)厚度不同的表面-本征层n-型重掺杂层(SIN~+)结构的GaAs样品的FKO.PR谱的FT分析表明，一部分样品的FT谱，包括其实部、虚部和模，与理论线性符合得比较好，由此求出轻空空(LH)和重空穴(HH)的约化质量平方根之比μ_1~(1/2)/(μ_h)~(1/2)对不同样品在0.805-0.816之间，同时也可以求出样品中的内建电场强度F_1，和调制光引起的调制电场δF=F_1-F_2。有一些样品的FT谱实部和虚部与理论线性差别很大，用FT的模仍可以给出有用的信息。

Thermal, mechanical and ionic conductive behaviour of gamma-radiation induced PEO/PVDF(SIN)-LiClO4 polymer electrolyte system

An effort has been made to modify the mechanical behaviour of our previously reported gel-type gamma-radiation crosslinked polyethylene oxide (PEO)-LiClO4 polymer electrolyte. A highly polar and gamma-radiation crosslinkable crystalline polymer, polyvinylidene fluoride (PVDF), was selected to blend with PEO and then subjected to gamma-irradiation in order to make an simultaneous interpenetrating network (SIN), which was used as a polymer host to impart stiffness to the plasticized system. Experimental results have shown that the presence of PVDF in the system, through gamma-radiation induced SIN formation, could not only give a rather high mechanical modulus of 10(7) Pa at ambient temperature, but also maintain the room temperature ionic conductivity at a high level (greater than 10(-4) S/cm). DSC, DMA and conductivity measurement techniques were used to examine the effects of blending, gamma-irradiation and plasticization on the variations of glass transition and melting endotherm, on the appearance of high elastic plateau and on the temperature dependence of ionic conductivity: In addition, it was found that, in contrast with the unplasticized system, the ionic conductivity mechanism of this gel-type electrolyte seems to conform to the Arrhenius model, suggesting that, as a result of the high degree of plasticization, the polymer chains act mainly as the skeleton of the networks or polymer cages to immobilize the liquid electrolyte solution, whereas the ionic species migrate as if they were in a liquid medium. (C) 1997 Elsevier Science Ltd.