Pressure effect study on the I－V property of the GaAs-based resonant tunnelling structure by photoluminescence measurement

This paper discusses the I-V property of the GaAs-based resonant tunnelling structure （RTS） under external uniaxial pressure by photoluminescence studies. Compressive pressure parallel to the [110] direction, whose value is determined by Hooke＇s law, is imposed on the sample by a helix micrometer. With the increase of the applied external uniaxial compressive pressure, the blue shift and splitting of the luminescence peaks were observed, which have some influence on the I-V curve of RTS from the point of view of the energy gap, and the splitting became more apparent with applied pressure. Full width at half maximum broadening could also be observed.     

Comparison between photoluminescence spectroscopy and photoreflectance spectroscopy in CuGaSe2 epilayer

Photoluminescence （PL） spectroscopy and photoreflectance （PR） spectroscopy are very useful techniques for studying the properties of materials. In this paper, the same material of Cu-rich metal-organic vapour phase epitaxy （MOVPE） grown CuGaSe2 layer is investigated in a temperature range from 20 to 300 K to compare these two techniques. Both PL and PR spectra appear red shifted, less intense and broadened. The temperature dependence of interband transitions is studied by using the Manoogian Leclerc equation. The values of the band gap energy at T=0K and the effective phonon temperature are estimated. The temperature dependences of intensities and broadenings of PL and PR spectral lines are also analysed. Based on the results of the comparison, the features and applications of the PL and PR can be shown in detail.     

小尺寸金纳米棒的快速制备及影响因素的研究

通过研究十六烷基三甲基溴化铵、抗坏血酸、NaBH4和AgNO3的用量,以及搅拌时间、反应时间对无种子生长法制备金纳米棒的影响,筛选出了最佳制备条件,以及各成分对金纳米棒生长过程中的作用.采用可见吸收光谱和透射电镜图对不同条件下所制备出的金纳米棒进行了表征.在室温为28℃,CTAB浓度为0.1 mol/L、AgNO3浓度为96μmol/L、AA浓度为0.97 mmol/L、NaBH4浓度为1.5μmol/L,搅拌25 s等最佳条件下,只需反应6h就能够成功制备出长径比为5且形貌均匀、分散性和稳定性良好、轴宽较小的金纳米棒,且有望应用于水环境中Hg2+的检测.     

基于斜光刻技术的SU-8胶三维微阵列结构制备

利用斜光刻技术替代传统的直光刻技术在相同底面积的基础上增大微阵列比表面积制备了高比表面积三维微阵列结构,.首先,利用MATLAB仿真对微阵列排布方式进行分析,确定最佳单个柱体宽度及阵列间距.实验中,采用两次甩胶法将SU-8光刻胶均匀旋涂在2寸硅基底上,甩胶转速设为1500r/min,旋涂时间设为35 s;分别置于65℃烘台上保持20 min和95℃烘台上保持70 min进行两次前烘处理;随后进行双向斜曝光,微柱宽度为20 μm,阵列间距为30 μm,光刻角度为20°.最后,再通过高低温后烘处理并显影30 min成功制备出了结构稳定的“Ⅹ”型三维微阵列结构.     

SOI基纳米光栅耦合器的结构改进与仿真验证

针对硅基光波导与单模光纤在光耦合过程中存在耦合效率低,对准难度大的问题,提出了一种新型基于绝缘体上硅(SOI)结构的纳米光栅耦合器。运用有限时域差分法探究了纳米光栅耦合器的结构特性,结合光纤准直器的准直原理,系统分析了纳米光栅耦合器的结构模型。研究了入射光波长、入射角度、光栅占空比等因素对光栅耦合效率的影响,得出了基本纳米光栅耦合器的最佳结构参数;在基本耦合光栅结构的基础上进行了改进,增加了后反射器、增透膜和底层介质膜,并运用Optiwave OptiFDTD 8.0软件优化了各部分结构的设计参数,得到了优化的耦合光栅结构。纳米光栅耦合器的耦合效率提高至59.37%,3dB带宽达到65nm。     

Abnormal Visible Luminescence Mechanism of Tb^3＋-Yb^3＋ Codoped SiOu-Al2O3-CaF2 Glass Studied by Time-Resolved Spectra

The upconversion energy transfer mechanism in Tb^3＋-Yb^3＋ co-doped SiO2-Al2O3-CaF2 glass is investigated by time-resolved spectra. The effect of donor ion Yb^3＋ is involved in the dynamic decay behavior of acceptor ion Tb^3＋, which provides direct proof for the energy transfer from Yb^3＋ to Tb^3＋. The pump power dependence curves show that the upconversion luminescence is a two-photon process. The measured decay curves of the 5D4 state （Tb^3＋） contain two parts： a slow decay process corresponding to its radiation, and a fast one with a decay parameter approximately twice the lifetime of the ^2F5/2 state （Yb^3＋ ）. The fast decay process is contradictory to the generally accepted cooperative sensitization upconversion rate equation model. Since the effect of the host environmental is excluded by comparative experiments, we believe that there should be another energy transfer mechanism in Tb^3＋-Yb^3＋ co-doped SiO2-Al2O3-CaF2 glass in addition to the cooperative sensitization process.     

Pressure effect study on the Ⅰ-Ⅴ property of the GaAs-based resonant tunnelling structure by photoluminescence measurement

This paper discusses the Ⅰ-Ⅴ property of the GaAs-based resonant tunnelling structure(RTS) under external uniaxial pressure by photoluminescence studies.Compressive pressure parallel to the [110] direction,whose value is determined by Hooke's law,is imposed on the sample by a helix micrometer.With the increase of the applied external uniaxial compressive pressure,the blue shift and splitting of the luminescence peaks were observed,which have some influence on the I-V curve of RTS from the point of view of the energy gap,and the splitting became more apparent with applied pressure.Full width at half maximum broadening could also be observed.     

Temperature dependence of biaxial strain and its influence on phonon and band gap of GaN thin film

Hexagonal GaN epilayer grown on sapphire substrate by metal organic chemical vapour deposition (MOCVD) is studied using Raman scattering and photoluminescence in a temperature range from 100\,K to 873\,K. The model of strain (stress) induced by the different lattice parameters and thermal coefficients of epilayer and substrate as a function of temperature is set up. The frequency and the linewidth of $E_2^{\rm high}$ mode in a GaN layer are modelled by a theory with considering the thermal expansion of the lattice, a symmetric decay of the optical phonons, and the strain (stress) in the layer. The temperature-dependent energy shift of free exciton A is determined by using Varshni empirical relation, and the effect of strain (stress) is also investigated. We find that the strain in the film leads to a decreasing shift of the phonon frequency and an about 10meV-increasing shift of the energy in a temperature range from 100\,K to 823\,K.