Semiconductor Quantum Dots Studied by Time-Resolved Luminescence Techniques

Abstract: In this thesis time-resolved photoluminescence spectroscopyis presented as a powerful tool to study the carrier dynamicsin various self-assembled quantum dot (QD) structures, whichare potentially attractive for device applications.The experiments reveal the impact of proton irradiation onInGaAs QDs and comparable quantum wells. Nonradiativerecombination at defects?an important material parameterand?measure?of the structure optical quality?is found to play a much less important role for the QD samples.The superior radiation hardness can be explained as a result ofthe three-dimensional carrier confinement in QDs. Comparisonsbetween the structures show a decrease of photoluminescenceintensity for quantum wells but a slight increase for QDsirradiated at low to intermediate doses. This somewhatunexpected characteristic is described by an enhanced carriertransfer into the dots via the defects introduced in thematerial by the protons.In a different structure carrier dynamics in spatiallyaligned of InAs QDs are investigated. Alignment along lines isachieved by misfit dislocations deliberately introduced in thesubstrate. Photoluminescence spectra of the dots exhibit muchsmaller inhomogeneous broadening than for the reference sampleas a result of an improved QD uniformity. Samples with varyingbuffer layer thicknesses were grown to study the influence ofdislocation related traps on the observed fastphotoluminescence decay. It is found that the fast carriertrapping is predominantly caused by point defects close to theQDs or at the QD/barrier interfaces.Additional numerical simulations confirm the roles of thetwo independently acting traps in nonradiativerecombination.