The role of dislocation-dislocation interactions in the relaxation of pseudomorphically strained semiconductors. II. Experiment-The high-temperature relaxation of ultrahigh-vacuum chemical-vapor-deposited SiGe thin films

Abstract

The thermal relaxation of SiGe films deposited by ultrahigh-vacuum chemical vapor deposition was studied by annealing the films for times up to 21/2 h at a temperature of 950 °C. Strain relaxation was determined by misfit dislocation density obtained by planar-view transmission electron microscopy and by double-crystal x-ray diffractometry. When the relaxation process requires relatively few dislocations (≲2 μm), the films relax to a remnant strain which is in agreement with previous experimental measurements; however, when higher densities of misfit dislocations were generated, substantially larger remnant strains were observed. This is interpreted as resulting from energetic interactions among the dislocations and analyzed in terms of the theory developed previously. It is found that the cutoff distance for dislocation interactions is substantially greater than the film thickness and a value of 1.4±0.5 μm is determined for 75-150-nm-thick films. Limited data from the literature also indicate a cutoff distance that is substantially in excess of the film thickness. In addition, as the annealing time is increased, a marked propensity for dislocation banding is observed, attesting to the mixed nature (attractive and repulsive) of the interactions.