Spectral probing of carrier traps in Si-Ge alloy nanocrystals

• Published in: Physica status solidi. PSS-RRL. Rapid research letters 2016-11, Vol.10 (11), p.824-827
• Main Authors: Ha, Ngo Ngoc, Giang, Nguyen Truong, Khiem, Tran Ngoc, Dung, Nguyen Duc, Gregorkiewicz, Tom
• Format: Article
• Language: English
• Subjects: Alloys; Boundaries; Carrier traps; Carriers; Crystal structure; Depletion; Ionization; Luminescence; Nanocrystals; Silicon base alloys; Silicon dioxide; Si−Ge alloys; transient induced absorption
• ISSN: 1862-6254; 1862-6270
• DOI: 10.1002/pssr.201600304

Photogenerated carriers in Si–Ge alloy nanocrystals (NCs) prepared by co‐sputtering method were investigated by mean of transient induced absorption. The carrier relaxation features multiple components, with three decay life times of τ ≈ 600 fs, 12 ps, and 15 ns, established for Si0.2Ge0.8 alloy NCs of a mean crystal size of 9 nm and standard deviation of 3 nm. Deep carrier traps, identified at the boundary between the NCs and the SiO2 host with the ionization energy of about 1 eV, are characterized by a long‐range Coulombic potential. These are responsible for rapid depletion of free carrier population within a few picoseconds after the excitation, which explains the low emissivity of the investigated materials, and also sheds light on the generally low luminescence of Si/Ge and Ge NCs. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) By means of transient induced absorption, deep carrier traps are identified at the boundary between S–Ge alloy nanocrystals and the SiO2 host. These traps are characterized by a long‐range Coulombic potential with ionization energy of about 1 eV and responsible for rapid depletion of photogenerated carriers within a few picoseconds. The study contributes towards better understanding of the generally low emission rates of Si/Ge nanostructures.