Effect of the surface upon misfit dislocation velocities during the growth and annealing of SiGe/Si (001) heterostructures Investigation of the recombination activity of misfit dislocations in Si/SiGe epilayers by cathodoluminescence imaging and the electron beam induced current technique

No abstract

A study of misfit dislocations in Si using the techniques of electron beam induced current (EBIC) and cathodoluminescence (CL) is presented. The dislocation recombination properties are found to depend on contamination. Dislocations in clean, as grown samples without D‐band luminescence have very low recombination activity, with an EBIC contrast c of about 0.3% at T = 80 K and without detectable contrast at 300 K. Ni contamination is shown to increase the dislocation contrast markedly and to lead to pronounced dark spots at 300 K. A negative c(T) slope is observed for dislocations, which is attributed to shallow centres. Another contrast mechanism acting at the dark spots is ascribed to charged Ni silicide particles. Dark CL dislocation contrast is observed at 5 K when using the substrate luminescence, caused by dislocation‐related reduction of exciton density. CL and EBIC correlate in a semi‐quantitative manner for all samples studied, suggesting that the same centres might be responsible for the CL and EBIC contrasts.

A brief account is given of some recent investigations of the luminescence associated with the presence of dislocations in silicon. These investigations show that transition metal contamination is necessary for dislocation related luminescence to be observed in plastically‐deformed float‐zone silicon and in material containing epitaxial and oxidation‐induced stacking faults. Cathodoluminescence spectroscopy and imaging measurements, and photoluminescence measurements on material with low densities of grown‐in dislocations, imply that the D3 and D4 luminescence features originate in the dislocation cores, whereas the D1 and D2 features are associated with point defects trapped in the strain fields of dislocations.

Photoluminescence (PL) spectroscopy, cathodoluminescence (CL) spectroscopy and imaging, and preferential defect etching and optical microscopy have been used to characterize compositionally graded Si1−xGex alloy layers grown by molecular beam epitaxy. Si1−xGex capping layers grown on the compositionally graded layers have low threading dislocation densities, and both PL and low-beam energy CL spectra show bound exciton luminescence features identical with those observed in bulk Si1−xGex alloys and relatively weak dislocation related D-band features. Increasing the beam energy increases the relative strength of the D bands in the CL spectra, indicating that they are associated with the misfit dislocations in the compositionally graded layer. This has been confirmed by combined chemical etching and PL spectroscopy measurements. The misfit dislocations can be observed by monochromatic CL imaging at a high-beam energy using a narrow band pass filter centerd on the D4 band.