Suppression of defect propagation in semiconductors by pseudomorphic layers
The propagation of defects in semiconductor heterostructures has been studied both theoretically and experimentally. The simple model shows that defects originating from lattice‐matched regions can be prevented from entering, or can be trapped by, a pseudomorphic layer, depending on the signs of the strain induced by the defect and the strain in the pseudomorphic layer. A pseudomorphic layer can therefore prevent the defect from propagating across in and entering the critical active region of a device. Experimentally, the photoluminescence intensities of Al0.4Ga0.6As/GaAs quantum wells with and without pseudomorphic In0.2Ga0.8As layers for prevention of defect propagation have been compared. GaAs substrates of high etch pit density were used to generate defects below the quantum well and silicon implantation was used to generate defects above it. The elevated temperatures during molecular‐beam‐epitaxial growth and postimplant rapid thermal annealing serve to assist in defect propagation in the respective ...
Effect of rapid thermal annealing on InGaAs/GaAs quantum wells
We have studied the effect of rapid thermal annealing (RTA) on highly strained InGaAs/GaAs quantum wells by using photoluminescence (PL) and double-crystal X-ray diffraction (DCXRD) measurements. It is found that a distinct additional PL emission peak can be observed for the annealed samples. This PL emission possesses features similar to the PL emission from InGaAs/GaAs quantum dots (QDs) with the same indium content. It is proposed that this emission stems from QDs, which were formed during the annealing process. This formation is attributed to the favorable diffusion due to the inhomogeneous strain distribution in the InGaAs layer intersurface. The DCXRD measurements also confirm that the dominant relaxation is strain enhanced diffusion under the low annealing temperatures.
Preparation of hydrophilic poly(vinyl butyral) hollow fiber membrane via thermally induced phase separation
Abstract Hydrophilic microporous hollow fiber membranes were prepared via thermally induced phase separation (TIPS). Poly(vinyl butyral) (PVB) and three kinds of polyethylene glycols (PEG) with the molecular weight of 200, 400 and 600 were used as polymer and diluents. In all cases, liquid–liquid (L–L) phase separation occurred and asymmetric cellular structures with the smaller pores at the outer surface were obtained. The properties of membranes such as pore size, water permeability, solute rejection and intensity were investigated by changing molecular weight of PEG, concentration of PVB, composition of the bath and air gap distance. The smaller molecular weight of PEG, the more PEG in the bath and the shorter air gap distance resulted in the higher water permeability, the lower solute rejection property and the lower mechanical strength.