Comparison of different grading approaches in metamorphic buffers grown on a GaAs substrate

Linear and logarithmic step thickness grading for ternary (In0.194Ga0.806As), cation graded, and quaternary (In0.485Ga0.515As0.4P0.6), anion graded metamorphic buffers have been investigated. The group III ratio was kept fixed during the quaternary growths. Comparison between the samples showed that using a higher grading slope at the beginning of the growth and decreasing the grading slope as the growth progresses leads to improvement in the quality of the metamorphic buffers. However, owing to the existence of phase separation, the quaternary buffers showed poorer quality of the final metamorphic pseudo-substrate layers than for the ternary graded metamorphic buffers.