Effect of growth temperature on the epitaxy strain relaxation and the tilt of InxAl1-xAs graded layer grown by solid-source molecular beam epitaxy

In this study, we investigate the effect of the molecular beam epitaxial growth temperature on the epilayer tilt and the strain relaxation in the InAlAs M-buffer layer when the In composition is varied linearly from 6 to 57% followed by an inverse grading to 52% where InAlAs is lattice-matched to InP. The samples grown at 420 and 500 degrees C have final epilayer tilts of 0.66-0.68 degrees about the [1 (1) over bar0] axis towards [(1) over bar(1) over bar0], whereas the sample grown at 370 degrees C has a smaller tilt of 0.15 degrees about the [1 (1) over bar0] axis but towards [110]. Cross-sectional transmission electron microscopy micrographs showed that the sample grown at 420 degrees C has the lowest dislocation density (6 x 10(6) cm(-2)) compared with those grown at 370 and 500 degrees C. The inversely graded layer in all samples was shown to be effective in reducing the strain that was accumulated during the forward graded layer. This resulted in close to fully relaxed epilayers (92-99%), which are necessary for the prevention of further occurrence of dislocation nucleation (an important criterion for subsequent device structure growth).