Dresden 2003 – scientific programme

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HL: Halbleiterphysik

HL 49: Poster II

HL 49.90: Poster

Thursday, March 27, 2003, 16:30–19:00, HSZ/P2

Ultrafast carrier and polarization dynamics in semiconductor nanostructures measured with THz experiments. — •Dmitry Turchinovich, Hanspeter Helm, and Peter Uhd Jepsen — Albert-Ludwigs Universität Freiburg, Dept. of Molecular and Optical Physics, Hermann-Herder-Str. 3, 79104 Freiburg

We present the results on ultrafast carrier and polarization dyamics in semiconductor nanostrucutres during and after the powerful optical femtosecond excitation. We study polarization dynamics in InGaN/GaN multiple quantum wells by measuring the THz emission from the samples. InGaN/GaN MQWs are of great interest because they comprize the regions with very strong built-in piezoelectric fields. Analysis of THz pulses generated at different pump levels reveals that at low pump levels the main contribution to ultrafast polarization dynamics is made by optical rectification of a fs laser pulse driven by a strong nonlinearity of the structure. At high pump levels the main contribution is made by the carriers created by two-photon absorption in MQWs. We also show results of optical pump-THz probe experiments on InAs/GaAs quantum dot structure. Using such technique we can measure free-carrier lifetime and mobility. We demonstrate that such structures, where QDs act as mid-gap traps for the electrons created in the barriers, are very promising for ultrafast optoelectronic applications, as they retain high mobility of epitaxial-quality GaAs and have short carrier lifetime due to efficient trapping of the carriers into the QDs.