Transiente Ladungsträgerdynamik und optische Verstärkung in III-V-Halbleitern

Im Rahmen dieser Arbeit wurde die Dynamik der optischen Verstärkung auf Grund intrinsischer Verluste in (GaIn)As und zum ersten Mal auch in dem neuartigen verdünnten Nitrid (GaIn)(NAs) untersucht. Es konnte gezeigt werden, dass die Zeitskalen des Abbaus der Verstärkung durch intrinsische Verluste be...

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Bibliographic Details
Main Author: Borck, Sebastian
Contributors: Rühle, Wolfgang W. (Prof. Dr.) (Thesis advisor)
Format: Doctoral Thesis
Published: Philipps-Universität Marburg 2006
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In this thesis the influences of intrinsic losses on the transient optical gain of the conventional III-V-semiconductor (GaIn)As and the novel dilute nitride (GaIn)(NAs) are investigated for the first time. It is shown that the timescales of the decay of optical gain at room temperature are in both cases comparable. At high excitation densities saturation and feeding processes from higher sub-bands dominate the gain dynamics at transition energies close to the fundamental band gap. In all experiments (GaIn)(NAs) behaves like an ordinary III-V-semiconductor, which shows that this material does not necessitate new concepts for the realisation of efficient lasers besides the optimisation of the growth parameters. Effects on transient optical gain or absorption due to different next-neighbour configurations of the nitrogen are not found. Measurements at high excitation densities show that optical gain can also be observed from higher sub-bands. In the second part of this thesis the material systems Ga(NPAs) and Ga(NAs) are investigated in respect to their suitability for the realisation of lasers based on GaP substrates. It is demonstrated for the first time that quantum-well heterostructures made of these materials with concentrations of about 3% nitrogen and 8% phophorus show lasing activity from cryogenic temperatures up to room temperature under optical excitation with ultrashort laser pulses. The lasing thresholds at low temperatures are found to be comparable for both material systems. An investigation of the threshold behaviour as a function of temperature reveals a higher characteristic temperature T0 of 86K for the Ga(NPAs) sample compared to 71K for the phosphorus free sample between 20K and room temperature. Measurements of the modal gain for the Ga(NPAs) sample at low temperatures using the Hakki-Paoli method yield values of at least 20/cm. Finally investigations are made of the decay of differential absorption for diluted nitrides. It is shown that in Ga(NAs) the characteristic lifetimes are reduced by about an order of magnitude from 125ps to about 10ps when the nitrogen contend is increased from 1% to approximately 3%. In a direct comparison indium containing (GaIn)(NAs) samples of similar nitrogen content generally show an increase in the lifetime of the carrier population. This effect is more pronounced at higher nitrogen concentrations (>2%) at which the lifetimes increase by a factor of more than two. Annealing of the (GaIn)(NAs) samples leads to a blue shift of the band gap and to slower decay of the differential signal. In the extreme case a quadruplication of the decay time from 30ps to 115ps is observed at concentrations of 2% nitrogen and 6% indium.