Characterization of compositionally graded Si1−xGex alloy layers by photoluminescence spectroscopy and by cathodoluminescence spectroscopy and imaging

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.