Influence of SiO2 and TiO2 dielectric layers on the atomic intermixing of InxGa1−xAs/InP quantum well structures
We have studied the influence of SiO2 and TiO2 dielectric layers on the atomic intermixing of InxGa1−xAs/InP quantum well structures using the impurity-free vacancy disordering technique. Photoluminescence results revealed that an enhancement of interdiffusion was obtained when the samples were capped with SiO2. Although TiO2 layers were able to suppress the interdiffusion in the InGaAs/InP system, the suppression was not significant compared to the AlGaAs/GaAs system. Based on a fitting procedure that was deconvoluted from the photoluminescence spectra as well as a theoretical modeling, the electron–heavy hole and electron–light hole transitions were identified, and a ratio of the group V to the group III diffusion coefficients (k) was obtained. The k ratio of the InGaAs/InP samples capped with SiO2 is relatively larger than that of samples capped with TiO2 layers.
Determination of interdiffusion coefficients of cations and anions in InGaAs/InP superlattice
The interdiffusion coefficients of cations and anions in InGaAs/InP superlattices (SLs) on their respective sublattices were analyzed quantitatively. Double crystal X-ray diffraction and simulation of the rocking curves based on dynamical diffraction theory were used to measure the interface strain that develops during rapid thermal annealing. Low temperature photoluminescence (PL) measurements were also done to assess the interdiffusion through the change in ground state transition energy of the SL. Simulation with the proper selection of the interdiffusion coefficients results in proper fitting of the interface strain profile and PL transition energies. Using this method, interdiffusion behaviors of InGaAs/InP SLs with and without SiO2:P capping were analyzed. Interdiffusion coefficients of 5.8×10−17 and 2.9×10−17 cm2/s were obtained for the anion and cation sublattices respectively, when the SL without SiO2:P was annealed at 800 °C.
EFFECT OF SAMPLE PREPARATION ON WATER TREE RESISTANCE OF XLPE/SEBS BLENDS
The effects of an aromatic polymer, such as poly[styrene-b-(ethylene-co-butylene)b-styrene] (SEBS), and its preparation processes on water tree resistance, morphology, crystallinity, dielectric constant and dielectric loss tangent of crosslinked polyethylene (XLPE)/SEBS and XLPE/SEBS/ethylene vinyl acetate (EVA) blends were investigated. The XLPE/SEBS samples were characterized by means of differential scanning calorimetry, scanning electron microscopy, dielectric spectral analysis and the accelerated water treeing experiment. The results clearly showed that although SEBS was partially compatible with LDPE and it was dispersed evenly in XLPE matrix, the blends demonstrated excellent dielectric performances, such as dielectric constant and dissipation factor. The crystallinity of XLPE/SEBS blends was decreased with increase in SEBS content and it was further decreased with the addition of EVA. SEBS could effectively improve the water-tree resistance of XLPE and both SEBS and EVA were found to improve the water tree resistance of XLPE synergistically as expected. The differences in sample preparation processes could change the phase morphology and dielectric performance of the blends, and could also influence the dispersion of SEBS in XLPE matrix as well as the crystallinity of the blends. Different preparation processes led to different water tree resistance behaviours of the samples. The improvement of SEBS dispersion in XLPE matrix helped to improve the water tree resistance of XLPE.