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

Abstract

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.

Raman and photoluminescence spectroscopy of SiGe layer evolution on Si(100) induced by dewetting

“…A rather broad PL band is observed ranging from about 0.6 eV to 0.9 eV in both cases. The absence of characteristic no-phonon (NP) and TO phonon peaks, which are typically observed for strained SiGe films, [33][34][35] indicates that the films are relaxed. 35,36 This is in agreement with the Raman data that showed the existence of only a weak strain in both films [ Fig.…”

Intrinsic Defects and the D1 to D4 Optical Bands Detected in Plastically Deformed Si

“…It does seem likely that the reconstructed cores favoured by theory 3 cannot lead to optical transitions as low as around 0.8 eV. Thus models based on gettered impurities like transition metals 4 , oxygen 5 or intrinsic defects like kinks and jogs 6 have been proposed. The prevalence of the bands -seen in FZ and Cz n-Si and p-Si as well as SiGe -gives doubt that impurities are primarily responsible while kink and jog densities are sensitive to annealing conditions.…”

Gettering Processes and the Role of Extended Defects

“…According to the literature, some impurity atoms in the dislocation core [205], dislocation jogs [206], segments of dislocations of special types (like Lomer dislocations) appearing due to dislocation reactions, multi-vacancies in the dislocation core [207] are typical examples of the possible origin of the D1 luminescence. When selecting a model it should be taken into account that the D1 band usually dominates the luminescence spectra in samples with a high local dislocation density (see, e.g., Figure 4.13(a)) where dislocations could interact with each other.…”