Effect of Highly Strained Superlattices on the Threading Dislocation Behavior in GaAs Grown on Silicon
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EFFECT OF HIGHLY STRAINED SUPERLATTICES ON THE THREADING DISLOCATION BEHAVIOR IN GaAs GROWN ON SILICON
N. A. El-Masry, J. C.L. Tarn Materials Science and Engineering Department, North Carolina State University, Raleigh, North Carolina 27695-7907 N.H.Karam* S.M.Bedair Electrical and Computer Engineering Department, North Carolina State University, Raleigh, N.C.27695-7911 * Currently with Spire Corp. Patriots Park, Bedford MA 01730 ABSTRACT GaAs films grown on silicon substrates suffer from a high density of threading dislocations. One technique to reduce these dislocations is the use of strained layered superlattices (SLS) InGaAs-GaAsP as buffer. We found that the effectiveness and interactions of the SLS with the threading dislocations strongly depend on the dislocation type and the strain field of the superlattices. Because of the high dislocation density in GaAs/Si, the SLS acts as a medium for dislocation interactions and annihilations. Highly strained SLS (- 2%) is required to bend the dislocations and keep them bent at the strained interfaces. We found that the combination between annealing and a highly strained superlattice coupled with selective epitaxy is an effective approach to reduce the threading dislocations in GaAs grown on Si. Transmission electron microscopy is used to study these effects. INTRODUCTION The growth of GaAs on Si substrates could lead to monolithic integration of optoelectronic devices with sophisticated Si electronic circuits and has received increasing attention in recent years. One difficulty that still impedes the progress of achieving device quality GaAs films on Si substrates is the high defect density in the GaAs epilayer. These defects result, in part, from stress generated due to the combination of lattice and thermal expansion coefficient mismatches between GaAs and Si. Considerable efforts have been made to suppress the propagation of defects to the epitaxial films. These approaches include thermal annealing [1], thermal strained layer [2], cyclic annealing [3], rapid thermal annealing [4] and the use of strained-layer superlattices (SLS) [5]. We have reported the effectiveness of InGaAs-GaAsP strained-layer superlattices (SLS) in blocking the threading dislocations in GaAs epilayers [5,6]. These SLS's have the advantage of accommodating a high level of strain (up to 2%) elastically without creating misfit dislocations. Further, we have studied the interactions which take place between the threading dislocations and the strain fields of the InGaAs-GaAsP superlattices [7]. By using these techniques, the dislocation density of GaAs Mat. Res. Soc. Symp. Proc. Vol. 130. C1989 Materials Research Society
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on Si was reduced. However, further reduction in dislocation density is required from the viewpoint of developing the aforementioned defect sensitive device. In this study, it is demonstrated that the threading dislocation density of GaAs on Si can be greatly reduced by using the combination of SLS and intermittant thermal annealing during or after SLS growth. The advantag
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