Photovoltaic properties and photoconductivity in multilayer Ge/Si heterostructures with Ge nanoislands

• Published in: Journal of materials science Vol. 46; no. 17; pp. 5737 - 5742
• Main Authors: Kondratenko, S. V., Vakulenko, O. V., Kozyrev, Yu. N., Rubezhanska, M. Yu, Naumovets, A. G., Nikolenko, A. S., Lysenko, V. S., Strelchuk, V. V., Teichert, C.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.09.2011; Springer; Springer Nature B.V
• Subjects: Analysis; Characterization and Evaluation of Materials; Classical Mechanics; Conduction band; Conduction bands; Crystallography and Scattering Methods; Elastic deformation; Electron transitions; Epitaxy; Germanium; Ground state; Heterostructures; Materials Science; Molecular beam epitaxy; Multilayers; Nanocomposites; Nanomaterials; Nanostructure; Photoconductivity; Photoelectric effect; Photoelectric emission; Polymer Sciences; Potential barriers; Raman spectra; Raman spectroscopy; Silicon; Silicon compounds; Solar energy industry; Solid Mechanics; Spectrum analysis; Valence band; Interband Optical Transition; Heavy Hole; Interband Transition; Valence Band State; Band Discontinuity
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-011-5528-2

Interband optical transitions in multilayer heterostructures with SiGe nanoislands were investigated using photocurrent spectroscopy and photo-emf. The n - p heterostructures containing Ge nanoislands in the area of the potential barrier were prepared by molecular-beam epitaxy at the temperature about 500 °C. It was shown that electron transitions from the ground state of the valence band in a nanoislands to the conduction band of Si surrounding made the main contribution into the vertical photo-emf in the range 0.75–1.05 eV, which is below the interband absorption edge of Si. The lateral photoconductivity observed in the range 0.63–0.8 eV at 77 K can be attributed to indirect interband transitions from the ground state of a nanoisland to L -state of the conduction band of a nanoisland. Analysis of Raman scattering spectra revealed that the Ge composition x in a nanoisland is about 0.87, while elastic deformation value amounts to ε xx  = −0.016. The calculated energies of interband transitions from the ground state of a nanoisland to the conduction band of Si surrounding (0.63 eV) and to L -state of the conduction band of a nanoisland (0.81 eV) fit the experimental data with a rather good accuracy.