Morphology, defect spectrum, and photoluminescence of thin Si0.7Ge0.3 layers

Results of experimental investigations of atomic structure and morphology of thin (8-30 nm) < 100 >-oriented undoped and boron-doped Si0.7Ge0.3 layers, deposited by atmospheric pressure chemical vapor deposition at 650 degrees C on silicon wafers, were presented in the first part of this paper. The second part is devoted to studies of influence of structural and morphological features of these films on their spectra of defect states N(E) and photoluminescence (PL). The N(E) distribution in the bandgap of our layers has been investigated with deep-level transient spectroscopy technique. The standard D1-D3 and dislocation-related defect levels were observed in the samples. The N(E) spectrum is not notably dependent on morphological features of the undoped layers, but defect density reduces significantly in the whole studied range of their energy at the layers doping with boron. The PL was excited with an argon ion (Ar+) laser at the sample temperature of about 5 K. Two PL peaks with energies of 1.10 and 1.08 eV, as well as PL lines at 0.82-0.85 eV (D-2), are detected in all studied samples. These PL features are originated from the no-phonon line of the Si substrate, as well as from phonon-assisted lines and dislocation-related defects of the Si0.7Ge0.3 layers, respectively. The intensities of the observed PL lines are influenced by the layer thickness, morphology, and doping. Possible mechanisms of interrelations between the films morphology, defect spectrum N(E), and the PL line strengths are discussed. (c) 2005 The Electrochemical Society.