We report the optimization of the properties of a strained interlayer (SIL) which is applied to reduce density of threading dislocations generated in an InP layer grown on GaAs. The effect of each SIL as a defect filtering layer was measured by X-ray diffraction on an InP layer which comprises the SIL. All the layers were grown by low-pressure metalorganic vapor phase epitaxy. Ternary compounds such as InGaP and InGaAs were investigated as materials for SILs. First In1-xGaxP was examined by varying its thickness and composition, and x = 0.2 with 400 Å thickness was found to be the most effective. The ways in which threading dislocations were reduced by SILs with different composition x were compared, in order to discuss the strain relaxation behavior in corresponding compounds. Examination of InGaAs revealed that not only the lattice parameter, but also other material properties affect the way in which the SIL reduce dislocations. We also found that an SIL which has a larger lattice constant that InP did not reduce dislocation density. These results are explained in terms of misfit dislocation networks, which are believed to be formed at SIL interfaces and to cause the dislocation reduction effect.
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