Low-density(~10^(9)cm^(-2)),long-wavelength(more than 1300 nm at room temperature)InAs/GaAs quantum dots(QDs)with only 1.75-mono-layer(ML)InAs deposition were achieved by using a formation-dissolution-regrowth method....Low-density(~10^(9)cm^(-2)),long-wavelength(more than 1300 nm at room temperature)InAs/GaAs quantum dots(QDs)with only 1.75-mono-layer(ML)InAs deposition were achieved by using a formation-dissolution-regrowth method.Firstly,small high-density InAs QDs were formed at 490℃,then the substrate temperature was ramped up to 530℃,and another 0.2 ML InAs was added.After this process,the density of the InAs QDs became much lower,and their size became much larger.The full width at half maximum of the photoluminescence peak of the low density,long-wavelength InAs QDs was as small as 27.5 meV.展开更多
Y2O3 nanomaterials have been widely used in transparent ceramics and luminescent devices. Recently there are many studies focusing on controlling the size and morphology of Y2O3 in order to obtain better materials per...Y2O3 nanomaterials have been widely used in transparent ceramics and luminescent devices. Recently there are many studies focusing on controlling the size and morphology of Y2O3 in order to obtain better materials performance. In present study, yttrium oxyhydroxide precursor was synthesized via a facile solvothermal process through the dissolution-re-crystallization mechanism of Y2O3 raw powders in the ethylenediamine solvent, then nanosized yttrium oxide crystal was prepared from the precursor through post heat treatment process. The effects of solvothermal treatment temperature, holding time, solvent kinds and post heat treatment parameters on crystalline structure, grain shape and size of nanocrystal were investigated by XRD, TEM and TGA-DTA measurements. TEM images reveal that the morphology of product after post heat treatment at 460℃for 12 h is rice-like nanocrystal. XRD shows that this product is pure cubic Y2O3 cphase. Present study reveals that high purity Y2O3 with rice-like morphology can be easily prepared with average size around 30 nm under suitable post heat treatment parameters. In addition, the effects of solvents such as water and ethanol etc. on the crystal structure and morphology were also investigated. It is suggested that dissolution-recrystallization process may be the main mechanism for the formation of nano-sized YOOH precursors under solvothermal reaction condition, and the ethylenediamine solvent is likely to play an important role in controlling the transformation process of yttria precursors to the Y2O3 nanocrystal.展开更多
Two kinds of InAs/GaAs quantum dot（QD） structures are grown by molecular beam epitaxy in formation–dissolution–regrowth method with different in-situ annealing and regrowth processes. The densities and sizes of qu...Two kinds of InAs/GaAs quantum dot（QD） structures are grown by molecular beam epitaxy in formation–dissolution–regrowth method with different in-situ annealing and regrowth processes. The densities and sizes of quantum dots are different for the two samples. The variation tendencies of PL peak energy, integrated intensity, and full width at half maximum versus temperature for the two samples are analyzed, respectively. We find the anomalous temperature dependence of the InAs/GaAs quantum dots and compare it with other previous reports. We propose a new energy band model to explain the phenomenon. We obtain the activation energy of the carrier through the linear fitting of the Arrhenius curve in a high temperature range. It is found that the Ga As barrier layer is the major quenching channel if there is no defect in the material. Otherwise, the defects become the major quenching channel when some defects exist around the QDs.展开更多
The Al0.85Ga0.15As layers buried below the GaAs core layer with and without the SiO2 layer were successfully oxidized in a wet ambient environment.The experimental results show that the SiO2 layer has little impact on...The Al0.85Ga0.15As layers buried below the GaAs core layer with and without the SiO2 layer were successfully oxidized in a wet ambient environment.The experimental results show that the SiO2 layer has little impact on the lateral-wet-oxidation rate of the Al0.85Ga0.15 As layer.The contrast of the SEM image of the oxidized regions and the absence of As-related Raman peaks for samples with the SiO2 layer arise from the removal of As ingredients with the largest atomic number,which leads to improvements in the thermal stability of the oxidized layer.The PL intensities of samples with the SiO2 layer are much stronger than those without the SiO2 layer.The PL emission peak is almost unshifted with a slight broadening under the protection of the SiO2 layer.This is attributed to the SiO2 layer preventing oxidation damage to the GaAs capping layer.展开更多
基金Supported by the National Basic Research Program of China(2013CB632104)the National Natural Science Foundation of China(60990315,61161130527 and 11274301).
文摘Low-density(~10^(9)cm^(-2)),long-wavelength(more than 1300 nm at room temperature)InAs/GaAs quantum dots(QDs)with only 1.75-mono-layer(ML)InAs deposition were achieved by using a formation-dissolution-regrowth method.Firstly,small high-density InAs QDs were formed at 490℃,then the substrate temperature was ramped up to 530℃,and another 0.2 ML InAs was added.After this process,the density of the InAs QDs became much lower,and their size became much larger.The full width at half maximum of the photoluminescence peak of the low density,long-wavelength InAs QDs was as small as 27.5 meV.
基金Project supported by SRF for ROCS, SEM (2003-14) and Science and Technology Department of Zhejiang Province (2003C11027)
文摘Y2O3 nanomaterials have been widely used in transparent ceramics and luminescent devices. Recently there are many studies focusing on controlling the size and morphology of Y2O3 in order to obtain better materials performance. In present study, yttrium oxyhydroxide precursor was synthesized via a facile solvothermal process through the dissolution-re-crystallization mechanism of Y2O3 raw powders in the ethylenediamine solvent, then nanosized yttrium oxide crystal was prepared from the precursor through post heat treatment process. The effects of solvothermal treatment temperature, holding time, solvent kinds and post heat treatment parameters on crystalline structure, grain shape and size of nanocrystal were investigated by XRD, TEM and TGA-DTA measurements. TEM images reveal that the morphology of product after post heat treatment at 460℃for 12 h is rice-like nanocrystal. XRD shows that this product is pure cubic Y2O3 cphase. Present study reveals that high purity Y2O3 with rice-like morphology can be easily prepared with average size around 30 nm under suitable post heat treatment parameters. In addition, the effects of solvents such as water and ethanol etc. on the crystal structure and morphology were also investigated. It is suggested that dissolution-recrystallization process may be the main mechanism for the formation of nano-sized YOOH precursors under solvothermal reaction condition, and the ethylenediamine solvent is likely to play an important role in controlling the transformation process of yttria precursors to the Y2O3 nanocrystal.
基金supported by the National Basic Research Program of China(Grant No.2013CB632104)the National Key Research and Development Program of China(Grant No.2016YFB0402302)
文摘Two kinds of InAs/GaAs quantum dot（QD） structures are grown by molecular beam epitaxy in formation–dissolution–regrowth method with different in-situ annealing and regrowth processes. The densities and sizes of quantum dots are different for the two samples. The variation tendencies of PL peak energy, integrated intensity, and full width at half maximum versus temperature for the two samples are analyzed, respectively. We find the anomalous temperature dependence of the InAs/GaAs quantum dots and compare it with other previous reports. We propose a new energy band model to explain the phenomenon. We obtain the activation energy of the carrier through the linear fitting of the Arrhenius curve in a high temperature range. It is found that the Ga As barrier layer is the major quenching channel if there is no defect in the material. Otherwise, the defects become the major quenching channel when some defects exist around the QDs.
基金supported by the National Research Project of China(Nos.60990315,60625402,61161130527)
文摘The Al0.85Ga0.15As layers buried below the GaAs core layer with and without the SiO2 layer were successfully oxidized in a wet ambient environment.The experimental results show that the SiO2 layer has little impact on the lateral-wet-oxidation rate of the Al0.85Ga0.15 As layer.The contrast of the SEM image of the oxidized regions and the absence of As-related Raman peaks for samples with the SiO2 layer arise from the removal of As ingredients with the largest atomic number,which leads to improvements in the thermal stability of the oxidized layer.The PL intensities of samples with the SiO2 layer are much stronger than those without the SiO2 layer.The PL emission peak is almost unshifted with a slight broadening under the protection of the SiO2 layer.This is attributed to the SiO2 layer preventing oxidation damage to the GaAs capping layer.
