Einfluß von Stickstoff auf die Photolumineszenz von metastabilen III-V-Nitriden

Sowohl in der Grundlagenforschung als auch auf dem Sektor der Optoelektronik hat sich in den letzten Jahren die Gruppe der verdünnt stickstoffhaltigen III-V-Halbleiter etabliert. Insbesondere das metastabile Materialsystem (GaIn)(NAs) ist aufgrund seines enormen Anwendungspotentials in den Bereichen...

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Bibliographic Details
Main Author: Hantke, Kristian
Contributors: Rühle, W. W. (Prof. Dr.) (Thesis advisor)
Format: Doctoral Thesis
Language:German
Published: Philipps-Universität Marburg 2005
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The group of metastable semiconductor compounds containing small amounts of nitrogen, the so called diluted III-V nitrides, has become very important in the fundamental research as well as in the optoelectronics over the last years. In particular the material system (GaIn)(NAs) is interesting due to its enormous application potential, e.g. optoelectronic integrated circuits, photovoltaics or telecommunication. The work presented here mainly summarizes experimental and theoretical results enlightening the material-specific, optical properties of (GaIn)(NAs). The primarily used experiment is the time-resolved photoluminescence spectroscopy. Thereby the samples are optically excited with an ultra-short pulse laser and the emitted signals are detected with a streak camera. All of the investigated samples were grown by metal-organic vapor phase epitaxy (MOVPE) in the same reactor. This enables to distinguish between material-specific properties and characteristics that are dependent on the growth process. It was shown in preliminary investigations that (GaIn)(NAs) cannot be simply understood as a superposition of the ternary semiconductor alloys (GaIn)As and Ga(NAs). Especially the post-growth treatment (annealing, hydrogenation) of the metastable material system leads to astonishing novel effects. A phenomenological model is presented and explains the dependence of the time-resolved photoluminescence on excitation density and temperature. The crucial point is the competition between the radiative recombination, the nitrogen-induced localization of charged carriers and the non-radiative recombination that is caused by energetically lower lying defect states. In the context of a hopping model, that describes the localization and disorder in semiconductors, the experimentally found effects are quantified not only by an analytically solvable rate-equation model but also by a kinetic Monte-Carlo simulation. The comparison of experiment and theory yields a simple exponential form for the density of localized states. Furthermore it can be confirmed that the typical energy scale of the localization is diminished by the annealing step as well as by the hydrogenation process. In a next step, the investigation of (GaIn)(NAs) epitactical layers, that were optimized for solar cell application, reveals astonishing features: The minority-carrier diffusion-length of the p-doped layers is found to be slightly higher than for the n-doped material implying that (GaIn)(NAs) solar cells with a p-on-n structure should be preferred in terms of higher quantum efficiency. Additionally the results show that the post-growth annealing becomes compulsory for efficient optoelectronic devices. Furthermore, the gallium precursor used in the MOVPE growth process should be Trimethylgallium instead of Triethylgallium. The former leads to a lower carbon contamination and to an improved performance after annealing. A new effect found during the investigations is the optimization of the internal quantum efficiency of the (GaIn)(NAs) structures after irradiation with intensive laser light attributed to the laser-induced annealing of defects. The final paragraph concentrates on the successful comparison of time-resolved photoluminescence, photo-modulated reflection measurements and a microscopic many-body theory. A profound understanding of the type-I type-II transition in (GaIn)As/Ga(NAs) heterostructures is achieved resulting in material-specific information as e.g. the temperature-dependent bandgap energies, the band offsets in Ga(NAs)/GaAs and (GaIn)As/Ga(NAs) respectively, as well as the interaction potential V­N dependent on the nitrogen content. Finally, the fundamental dependence on excitation density investigated in the experiment is theoretically quantified not only for the photoluminescence intensity and but for the lifetimes, too. The universal implications for the high-density regime are of substantial importance for semiconductor laser applications.