Narrow Ge layers embedded in Si are investigated using photoluminescence (PL) spectroscopy. With increasing layer thickness a growth mode changeover from two-dimensional (2D) strained-layer growth to three dimensional Stranski–Krastanov growth is observed. Additional PL lines that are redshifted with respect to the PL signal of the 2D strained layers are attributed to islands formed by three-dimensional growth. The occurrence of these new lines is accompanied by a blueshift of the PL of the 2D layers, indicating a strong Ge diffusion from the 2D layers towards the islands.
lnterband optical transitions have been studied in a variety of short-period Si/Ge superlattice structures by means of photocurrent spectroscopy, infrared absorption, photo-and electroluminescence. Furthermore, the bandgap photoluminescence from strain-adjusted Si , Ge, (m = 9, 6, 3; n = 6, 4, 2) adjustment was achieved by a thick, step-graded Si,_,Ge, buffer layer resulting in an improved quality of the superlattice with respect to dislocation density. The hydrostatic pressure dependence was modelled using an approach based on deformation potentials and effective-mass theory. In samples annealed at 500 "C and higher, a systematic shifl of the bandgap was observed which is discussed in terms of a process Involving interdiffusion of the Si and Ge atoms. Bandgap-related electroluminescence was observed in mesa diodes at room temperature, whereas the photoluminescence disappeared at about 40 K. The electroluminescence from samples based on different buffer-layer concepts is compared.Apart from the strain-symmetrized Si/Ge superlattices, another structure that has been proposed to act as an efficient, light-emitting device in the Si-based systems is an ultrathin Ge layer (1-2 monolayers) embedded in bulk Si. We report on the electroluminescence spectra at various temperatures from a sample based on this concept, namely a layer sequence consisting of two periods of Si ,,Ge, grown pseudomorphically on an n+ Si substrate. A very intensive, well resolved electroluminescence was obtained at 55 K from the ow.sgper!a!!ices was studied under applied hydrostatic prees~re, The strain
We report on detailed studies of the bandgap of Si/Si,Ger-, quantum well structures grown on (001) Si by molecular beam epitaxy. Photocurrent and photoluminescence spectroscopy are used t t determine the bandgap of the SiGe alloy up to x = 0.67. We found that interdiffusion of the SiGe layers limited the maximum Ge content in the alloy layers at a high growth temperature (720°C). At a lower growth temperature (500'C) diffusion is negligible. This is verified by pi-n structures and p-type modulation-doped quantum wells. In the modulation-doped samples the bandgap could be reduced to 1.5 wm while still showing intense bandgap related photoluminescence. As well as an alloy-related onset the p i -n diodes reveal a low-energy threshold, which is defect related. Low growth temperatures lead to defects located in the SiGe layers. Raising the number of quantum wells and Ge content up to almost critical thickness we found a maximum external responsivity of 4 x mesa-type pin photodiodes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.