The effect of ion irradiation on the thermal stability of GeSi/Si strained-layer heterostructures

Double Crystal X-ray Diffraction (DCXRD), Transmission Electron Microscopy (TEM), and Rutherford Backscattering Spectrometry and Channelling (RBS-C) are used to study the effect of ion irradiation on the strain and strain relaxation of metastable Ge_xSi_1-x/Si strained layers. Room temperature irradiation within the alloy layer is shown to increase the measured lattice strain, behaviour which is well modelled by assuming a strain profile which is based on the excess interstitial distribution created by the irradiation. During annealing to 650°C the radiation damage evolves into intermediate defect complexes and dislocation loops, and misfit dislocations nucleate and grow. The interactions between these different defects can result in a complex strain relaxation sequence which depends on the relative strain contributions of the defects and their relative nucleation and growth behaviour. Strain relaxation can therefore be enhanced or retarded by the ion-irradiation depending on the irradiation fluence and annealing temperature. Evolution of strain in irradiated Ge_xSi_1-x/Si alloy layers is discussed with reference to the defect microstructure after irradiation and annealing.