Dependence of Threading Dislocation Density on Substrate Misorientation in In 0.15 Ga 0.85 As Grown on GaAs(100)
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Dependence of Threading Dislocation Density on Substrate Misorientation in In0.15Ga 0 .85As Grown on GaAs(100)
P.N. Uppal, J.S. Ahearn, and R. Herring Martin Marietta Laboratories 1450 South Rolling Road Baltimore, MD 21227
ABSTRACT The density and arrangement of dislocations in In0 . 15Gao 85As grown on GaAs(I(X)) were determined by transmission electron microscopy as a function of misorientation toward (I I I)A, (I I I)B, and (110). Strained layer superlattices were used in all cases to reduce dislocation density. Layers grown on exact GaAs(100) exhibited a non-uniform threading dislocation distribution whereby some areas had a high density
(-
l09 cm 2 or higher) of dislocation tangles and
other areas that we in between had a more uniform density (- 2 x 10 cm-2). The misorientated layers exhibited a uniform threading dislocation distribution with densities of - 5 x (100) misoriented towards (11 1)A,
-
1 x 107 cm 2 towards (11 1)B, and
-
106
cm1-2 for
3 x 10 7 cn" 2 towards
(110). The misfit dislocation network (dislocations located at the GaAs-ln00 .1 5Ga 0 .85 As interface) formed orthogonal dislocation arrays in the case of exact (100) substrates and slightly non-orthogonal arrays in the case of misoriented substrates. These results are explained with the help of a general glide model of strain relaxation in which the exact (100) orientation has eight equally stressed glide systems which presumably activate during strain relaxation. With misoriented substrates the stress symmetry is broken and fewer glide systems experience the maximum stress, thus reducing the number of active dislocation systems. A small asymmetry in interfacial dislocation density was observed in all the cases where the linear dislocation density along the two (011) and (011) orthogonal directions differed by about 20%. This is explained by the preferred activation of (x-dislocations (high dislocation mobility) over 13-dislocations (low dislocation mobility).
INTRODUCTION Lattice-mismatched epitaxial growth is of great technological interest because success in improving material properties in lattice mismatched systems would significantly broaden the choice of material systems available for practical device applications. For example, the Mat. Res. Soc. Symp. Proc. Vol. 145. @1989 Materials Research Society
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ln\Ga 1,.As/GaAs system is of recent practical interest for advanced transistor and laser applications. The IniGa .•As/GaAs system is also of significant interest from the fundamental materials point of view because the misfit strain can be determined by the choice of the InImole fraction so that carefully, controlled experimental investigations of strain relaxation in mismatched epitaxy systems as a function of misfit strain can be made. In mismatched epitaxy, above the critical thickness for introduction of dislocations, a high density of dislocations is introduced at the InGa1 ,-As/GaAs interface to alleviate lattice mismatch strain. Some of the interface dislocations thread through the epilayer, following the growth
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