Combined Tem and X-Ray Topographic Characterization of In x Ga 1-x As/GaAs Strained Layer Systems.
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COMBINED TEM AND X-RAY TOPOGRAPHIC CHARACTERIZATION OF In.Ga,_TAs/GaAs STRAINED LAYER SYSTEMS. MICHAEL DUDLEY*, GONG-DA YAO*, DAVID PAINE", DAVID HOWARD"
AND
ROBERT N. SACKS***. *
Dept. of Materials Science & Engineering, SUNY at Stony Brook, NY 11794; Brown U., Div. of Eng., Providence, RI 02912. United Technologies Research Center, East Hartford, CT.
ABSTRACT. Novel application of a combination of TEM and non-destructive synchrotron X-ray topography in both Bragg and grazing Bragg-Laue geometries to the characterization of In.,Ga,.,As/GaAs strained layer films is reported. Specialized epilayer lift-off procedures enabled TEM characterization of the defect distributions in macroscopic area films, effectively increasing the field of view of the technique by several orders of magnitude. These lateral distributions correlated well with those observed on both Bragg and grazing BraggLaue topographs. Grazing Bragg-Laue images also afforded depth sensitivity. Excellent correlations exist between results obtained with all these techniques for systems with a wide range of In concentrations, corresponding to a broad range of interfacial dislocation densities, although only results for x=0.085 are presented. This work demonstrates that it is possible to bridge the gap that has traditionally existed between the areas of application of these two generic techniques, in terms of both tolerable defect densities and fields of view. This gap also spans the range of defect densities which is of interest in this and other systems.
INTRODUCTION. The study of the onset of strain relaxation is of great importance to the realization of useful devices based on semiconductor heterostructures. One promising strained-layer system is InGal_,As/GaAs which has been successfully implemented in the fabrication of pseudo-morphic MODFET's. While there has been great progress in the growth of strained heterostructures in general, and in the In.Ga 1 _.,.As/GaAs system in particular, questions about the mechanisms of strain relief via dislocation formation still remain. The study of mechanisms and kinetics of dislocation nucleation and propagation in strained-layer systems is essential both to the fundamental understanding of defects in pseudomorphically grown thin films and to guide future device development. Strain relaxation, either during growth or during subsequent processing, begins with the glide of pre-existing threading defects. These threading defects are grown into the strained layer from defects in the substrate. Above the critical thickness [1], these dislocations glide, at a rate determined by the kinetics of dislocation motion, to lay down lengths of interface misfit that lie parallel to one of the two in-plane < 110 > directions. Before heterogeneous nucleation processes begin to operate, the separation between the lines of interface misfit dislocations is relatively large since substrate material typically contains relatively few defects. Consequently, the study of the onset of relaxation requires a technique capable of detecting
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