BOND LENGTH RELAXATION IN ULTRATHIN GAXIN1-XP AND INPXAS1-X LAYERS ON INP(100)

The bond length relaxation in strained-layer GaxIn1-xP and InPxAs1-x alloys epitaxially grown on InP(100) by OMVPE has been investigated by surface-sensitive EXAFS on the Ga K and As K edges using synchrotron radiation. The bond lengths.in the two ternary alloys were studied as a function of composition x (0. 15 less-than-or-equal-to x less-than-or-equal-to 0.7) and film thickness from 1000 down to 20 angstrom. The observed bond lengths in thick epilayer (1000 angstrom) of both GaxIn1-xP and InPxAs1-x alloys agreed well with the values estimated for bulk alloys, indicating that the strain is uniformly relaxed. However, we found that the bond length in ultrathin strained-layers relaxation is not uniform among the bond pairs and the tetragonal distortion distributes according to the relative values of force constants alpha(ij) and beta(ij).