Anomalous tilting in InGaAs graded buffers from dislocation sources at wafer edges

Uniform strain relaxation and defect densities across the entire wafer are important aspects of lattice-mismatched or metamorphic epitaxy of semiconductors. Achieving this requires an understanding of the sources of dislocations that lead to relaxation. We show that wafer edges are a major source of misfit dislocations in InGaAs graded buffers on GaAs substrates. AlInP solar cells fabricated from regions on the wafer affected by edge sources have a markedly lower performance due to a local increase in the threading dislocation density. Spatially resolved x-ray reciprocal space maps and electron backscattered diffraction maps of the InGaAs compositionally graded buffer reveal anomalous epi-layer tilting on 2-inch substrates from these dislocation sources at the wafer edge. The tilting abruptly changes direction partially through the graded buffer growth as the dislocations from the wafer edge appear in the x-ray sampling areas. We speculate that anisotropic misfit dislocation glide in III-V materials in combination with non-uniform stress states during growth biases slip system activity. These experiments demonstrate that lattice-mismatched epitaxy requires additional controls over the growth environment to achieve uniform strain relaxation for wafer scale heterogeneous integration.