Overshoot Graded Layers for Defect Engineering in Heteroepitaxial Semiconductor Structures

摘要

Overshoot graded layers are of interest for controlling defect densities in heteroepitaxial semiconductor devices. We studied dislocation densities in ZnS_ySe_(1-y)/GaAs (001) structures with overshoot graded buffer layers. In each structure, a uniform device layer was grown on a graded buffer. Structural characterization was by high-resolution x-ray diffraction. In forward-graded structures, an overshoot interface with 0.1% mismatch removed 2 × 10 cm~(-2) dislocations from the top layer. This indicates that dislocations are bent over at the overshoot interface by a Matthews and Blakeslee or half loop closure mechanism, and the average misfit segment length was ～ 4 × 10~(-4) cm. Reverse-graded structures had significantly higher (～2x) dislocation densities than forward-graded structures, due to enhanced dislocation generation in the early stages of epitaxial growth. The inclusion of overshoot did not significantly affect the dislocation densities in reverse-graded structures.