Misorientation and tetragonal distortion in heteroepitaxial vapor-Grown III–V structures

Heteroepitaxial deposits of III–V vapor phase epitaxy (VPE) alloys on (001) substrates have been found to exhibit distortions such that: 1. the epitaxial layers are not parallel to the substrate but are inclined to it by as much as 2°, and 2. the epitaxial lattice is tetragonally distorted normal to the substrate with c/a ratios as high as 1.003. These effects habe been observed in non-graded (abrupt) and in compositionally graded (both step and continuous) layers of InxGa1−xP, GaAsxP1−x, and InxGa1−xAs on GaAs and GaP substrates and vary with the amount of lattice mismatch. Misorientation is shown to be a general phenomena in VPE growth associated with relieved lattice mismatch (regardless of the grading technique employed), whereas tetragonal distortion is felt to be a manifestation of the Poisson effect normal to the substrate associated with unrelived lattice mismatch and is shown to be dependent on grading technique. Possible device effects are also discussed.