Stress Dependence of the Velocity of Threading Dislocation Segments in Si - Ge Heteroepitaxial Films.
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STRESS DEPENDENCE OF THE VELOCITY OF THREADING DISLOCATION SEGMENTS IN Si - Ge HETEROEPITAXIAL FILMS. VERONIQUE T. GILLARD*, DAVID B. NOBLE** AND WILLIAM D. NIX* * Stanford University, Department of Materials Science and Engineering, Building 550, Stanford, CA 94305 ** Currently at Spectrum Analysis Inc., 39500 Stevenson Place, Suite 103, Fremont, CA 94539 ABSTRACT This paper presents data for threading dislocation velocities measured in Si-Ge heteroepitaxial thin films during in situ HVTEM annealing experiments. These data are compared to three models which were previously developed to describe the kink mode of dislocation motion. Two of these models, Hirth and Lothe [1] and Seeger-Schiller [2], are based on the discrete narrow kink representation. The other, developed by Biittiker and Landauer [3], is based on the macroscopic bulge model representation of the dislocation line. It is found that both the narrow kink models underestimate dislocation velocities in the stress range of the experiments and that a good representation of the data can be obtained by using the macroscopic bulge model in the dislocation length-dependent regime.
INTRODUCTION Strain relaxation in semiconductor heteroepitaxial films with lattice mismatch occurs mainly by the propagation of threading dislocation segments in the strained film. This phenomenon has been investigated extensively, see for example [4, 5, 6, 7]. A good understanding of the kinetics and mechanisms of relaxation is key to the development of reliable devices based on heteroepitaxial structures. The principal parameters controlling this kinetic process are the density of mobile threading dislocations and their velocity. In a previous paper [8], we showed that it is possible to determine the mobile dislocation density and its evolution during the course of relaxation by making in situ measurements of wafer curvature during isothermal annealing experiments. Determination of the mobile dislocation density in these experiments requires previous knowledge of threading dislocation velocities and of the effect of stress and temperature on velocity. TEM observations of the motion of such dislocations provided the necessary velocity information for films similar to those investigated in our annealing experiments. Here, we compare velocity data obtained with the TEM technique to models previously developed [1, 2, 3, 9] for the motion of dislocations in semiconductors. Semiconductors have a high lattice resistance to dislocation motion and therefore exhibit a very high Peierls stress, (over 2 GPa for bulk Si.) At stresses below the Peierls stress, dislocations can move by the nucleation and motion of kink pairs along the dislocation line. There are several models available to describe this kink mode of dislocation motion. One of the most popular is that of Hirth and Lothe [1] which predicts that the dislocation velocity varies linearly with the resolved shear stress and that the activation energy for dislocation motion is independent of stress: 2v abh 2 kT
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