Morphology, Defect Spectrum, and Photoluminescence of Thin Si[sub 0.7]Ge[sub 0.3] Layers

Abstract

Results of experimental investigations of atomic structure and morphology of thin ͑8-30 nm͒ ͗100͘-oriented undoped and borondoped Si 0.7 Ge 0.3 layers, deposited by atmospheric pressure chemical vapor deposition at 650°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 N͑E͒ and photoluminescence ͑PL͒. The N͑E͒ 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 N͑E͒ 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 Si 0.7 Ge 0.3 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 N͑E͒, and the PL line strengths are discussed.