Defect Reduction in GaAs Epilayers on Si Substrates Using Strained Layer Superlattices
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Defect Reduction in GaAs Epilayers on Si Substrates Using Strained Layer Superlattices by N. El-Masry, N. Hamaguchi, J.C.L. Tarn, N. Karam, T.P. Humphreys, D. Moore and S.M. Bedair Electrical and Computer Engineering Department North Carolina State University Raleigh, North Carolina 27695 J. W. Lee and J. Salerno Kopin Corporation Taunton, Massachusetts
ABSTRACT
In.Gal- 1 As-GaAsl-yPy strained layer superlattice buffer layers have been used to reduce threading dislocations in GaAs grown on Si substrates. However, for an initially high density of dislocations, the strained layer superlattice is not an effective filtering system. Consequently, the emergence of dislocations from the SLS propagate upwards into the GaAs epilayer. However, by employing thermal annealing or rapid thermal annealing, the number of dislocation impinging on the SLS can be significantly reduced. Indeed, this treatment greatly enhances the efficiency and usefulness of the SLS in reducing the number of threading dislocations. Transmission electron microscopy techniques have been used to characterize the dislocation behavior.
The growth of GaAs on Si substrates enables the integration of III-V compound based devices and Si electronic circuits. To date, several approaches have been investigated for the deposition of GaAs IlI-V compounds on Si substrates. These methods include, the use of a Ge intermediate layer,() direct deposition using molecular beam epitaxy,(2) metalorganic chemical vapor deposition(3) and laser stimulated deposition(4). However, one of the major difficulties in this technology is the generation of a high density of defects in the GaAs epitaxial layers. Recently, several schemes have been successfully employed to reduce the density of defects. These approaches include thermal anneal7 ing,(5) rapid thermal annealing(o) and the use of strained layer superlattices (SLS).( ) The corresponding SLS structures that have been studied include, InxGal-xAs-GaAs(2) and GaAs, -Px-GaAs('). As a consequence of using these SLS buffers layers, a significant reduction in the dislocation density has been obtained. However, despite these results the SLS composed of ternary-binary (GaAs) systems cannot be grown lattice matched to the GaAs substrate. Indeed, this SLS structure which as a whole has a lattice constant which corresponds to the ternary material with composition of x/2, has several inherent shortcomings. In particular, the total thickness of the SLS should be less than the critical thickness, he, in order to prevent the generation of misfit dislocations at the GaAs substrate/SLS interface(')- Consequently, this will limit the number of periods and Mat. Res. Soc. Symp. Proc. Vol. 91- 1987 Materials ResearchfSociety
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therefore, the number of interfaces capable of suppressing the propagation of thrmading dislocations. Furthermore, the binary-ternary SLS will also limit the amount of strain that can be present between successive layers in the SLS. Indeed, it has been previously reported(7) that when the In.Ga 1 1,As-GaAs SLS has a t
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