Parts | Days | Selection | Search | Downloads | Help
HL: Halbleiterphysik
HL 24: Poster II
HL 24.74: Poster
Thursday, March 29, 2001, 10:30–19:00, Rang S\ 3
Femtosecond spectroscopy of low-temperature GaAs — •Tobias Korn, Antonia Jaye, Sandra Schnuell, and Ingrid Wilke — Institut für Angewandte Physik der Universität Hamburg, Jungiusstraße 11, 20355 Hamburg
We have measured the photocarrier lifetime in low-temperature epitaxially grown GaAs by an optical femtosecond degenerate pump-probe experiment. Lock-in-techniques are used to detect the transient reflectivity changes Δ R caused by photocarrier generation and trapping. Due to the MBE growth process at low substrate temperatures between 200∘C and 250∘C an excess of As is incorporated. This causes a high defect density of ≈1019 cm−3, leading to ultrafast carrier trapping. The samples we have investigated show trapping times shorter than 400 fs, depending on growth temperature. Using a He-flow-cryostat, we were newly able to determine the trapping times for sample temperatures ranging from 45 K to room temperature. Our measurements show that the trapping times are independent of sample temperature. Although we use lock-in-techniques to detect the reflectivity changes, we observe a strong background signal in the reflectivity transients, which we attribute to thermoreflectance changes caused by local heating of the sample. This background signal can be reduced significantly by lowering the sample temperature.