We present methods and results of investigation of the local strain and stress at atomic scale in highly stressed GaN/Saphire and GaAs/CdTe buffer layers.
Grow of the layer with big mismatch up to 15 % of lattice parameter generate huge density of defects. Understanding of the relaxation processes are important for optimisation of technology of growth of the buffer layers used as substrate for quantum structures.
The defect density can be reduced by technological parameters directed to amplification of different relaxation processes occurred at atomic scale as dislocation annihilation, bending of dislocation line to heterointerface, creation of misfit dislocation network at this interface etc. All this mechanisms are dynamic and depends on the dislocation movement in stress field generated by other defects.
So, for understanding and for creation a theoretical description of such processes, it is necessary to obtain quantitative information about 3d distribution of stress fields around isolated and interacted defects.
We propose an approach, which starts from high resolution transmission electron microscopy images taken in zone axis, where defect's Burgers vector components are not zero. The two dimensional strain fields are extracted by image processing using Geometric Phase method, which allows precisely measurement of lattice fringes shift in deformed zone in relation to no deformed lattice.
The experimental lattice distortion data are read by finite element (FE) program into nodes of the tree dimensional mesh as initial solution. Boundary condition corresponding to bulk as well as to TEM specimen geometry was applied. After several FE iterations the stress field around dislocation core was determined in atomic scale in three dimensions.In FE calculations the anisotropy and no-linear elasticity were taken in to account.
The validity of our procedure was checked by treatment of simulated images obtained from model of dislocation with know distortions.