In dieser Dissertation wird zum einen die ultraschnelle Ladungsträgerkinetik in einem Galliumnitrid (GaN)-basierten Übergitter, zum anderen die piezoelektrische Elektron-Phonon-Wechselwirkung kohärenter zonengefalteter Phononen in Galliumarsenid (GaAs)-basierten Übergittern behandelt. Mittels spektral- und zeitaufgelöster Photolumineszenzmessungen an einem n-dotierten GaN/Al0,18Ga0,82N Übergitter mit Parametern ähnlich derer in optoelektronischen Bauelementen wurde die defektbedingte Ladungsträgerkinetik untersucht, die innerhalb von ca. 150 ps durch den Einfang in tiefe, nichtstrahlende Rekombinationszentren beeinflusst wird. Die Untersuchung einer Passivierung mit Siliziumnitrid zur Verhinderung von Degradationseffekten zeigte ein stabiles optisches Langzeitverhalten bei gleichzeitiger Zunahme nichtstrahlender Defekte. Ferner wurde mit spektral aufgelöster Anrege-Abfrage-Spektroskopie eine Einfangkinetik auf einer Zeitskala von 150 - 200 fs in Defektzustände nahe der Übergitterbandkante gemessen, gefolgt von der Abkühlung der Ladungsträger durch Phononemission innerhalb weniger Pikosekunden bei Raumtemperatur und 35 ps bei 5 K. Kohärente zonengefaltete Phononen wurden mit Anrege-Abfrage-Spektroskopie an zwei AlAs/GaAs-Übergittern untersucht, die in [100]-, bzw. [111]-Richtung gewachsen wurden. Dies ermöglicht die (gezielte) Untersuchung der piezoelektrischen Elektron-Phonon-Kopplung, da diese für longitudinal-akustischen Phononen nur in der [111]-Probe existiert. Die Amplitude kohärenter Phononen mit einem Wellenvektor von q=0 in der [111]-Probe fällt verglichen mit denen in der [100]- und der [111]-Probe mit q≠0 signifikant schneller ab. Kohärente Phononen verursachen in der [111]-Probe bei q=0 ein makroskopisches piezoelektrisches Feld, welches Ladungsträger beschleunigt, die durch Reibung kohärente Phononen dämpfen. Bei hohen Ladungsträgerdichten unterdrückt die Abschirmung der induzierten piezoelektrischen Felder diese zusätzliche Dämpfung. / In this dissertation, the ultrafast carrier dynamics in a gallium nitride (GaN)-based superlattice as well as the piezoelectric electron-phonon-coupling of coherent zone-folded phonons in gallium arsenide (GaAs)-based superlattices are addressed. Using spectrally and time-resolved photoluminescence experiments on an exemplary n-doped GaN/Al0.18Ga0.82N superlattice with parameters similar to those in optoelectronic devices, we investigated the defect-related carrier kinetics, that are affected by trapping in saturable nonradiative recombination centers on time scales of ~150 ps. The investigation of a passivation with silicon nitride to prevent degradation effects show a long-term optical stability with a concomitant increase in non-radiative defect densities. Furthermore, spectrally resolved pump-probe spectroscopy was used to measure trapping kinetics into defect states near the conduction band minimum on a time scale of 150 – 200 fs. These kinetics are followed by carrier cooling through phonon emission within a few picoseconds at room temperature and within 35 ps at 5 K. Coherent zone-folded phonons were studied with pump-probe spectroscopy on two AlAs/GaAs superlattices grown in [100] and [111] direction, respectively. This allows the specific investigation of the piezoelectric electron-phonon interaction, since this exists for longitudinal acoustic phonons only in the [111] sample. The amplitude of coherent phonons with a wave vector of q=0 in the [111] sample decays significantly faster than in the [100] and the [111] samples with q≠0. Coherent phonons in the [111] sample cause a macroscopic piezoelectric field to which the photogenerated electron-hole plasma couples. Friction of the accelerated carriers provides the additional damping mechanism. High carrier densities screen the induced piezoelectric field, thus reducing the damping mechanism via the piezoelectric interaction.

This work summarizes properties of nitrogen containing GaAs, which are relevant for optoelectronic application and allow a deeper insight in the physics of this material. In the first part the dependence of the banggap energy of nitrogen implanted GaAs on several process parameters (implanted nitrogen concentration, implantation temperature, annealing duration and temperature) is investigated. The second part focuses on the relaxation dynamics of highly excited carriers. For this, the carrier relaxation dynamics in nitrogen implanted GaAs, in epitaxially grown GaAsN and in (pure) GaAs are investigated by means of pump probe measurements on a femtosecond time scale. The comparision of experimental results to calculated scattering rates leads to relevant informations of scattering mechanisms and electronic properties. / Diese Arbeit widmet sich Eigenschaften von Stickstoff-haltigem Gallium-Arsenid, die sowohl für das physikalische Verständnis als auch für optoelektronische Anwendungen dieses Materials relevant sind. Im ersten Teil dieser Arbeit wird die Abhängigkeit der Bandlücken-Energie von verschiedenen Prozess-Parametern (Stickstoffkonzentration, Implantationstemperatur, Ausheildauer und -temperatur) in Stickstoff-implantiertem GaAs untersucht. Der zweite Teil konzentriert sich auf die Relaxationsdynamik hoch angeregter Ladungsträger. Neben dem oben bereits angesprochenen Material wird in Anrege-Abfrage-Experimenten mit Femtosekunden-Zeitauflösung zusätzlich epitaktisch gewachsenes GaAsN und (Stickstoff-freies) GaAs untersucht. Die Berechnung der Streuraten und der Vergleich mit experimentell gewonnenen Daten liefert wesentliche Informationen über beteiligte Steumechanismen und elektronische Eigenschaften.

Semiconductor quantum dots (QDs) are fascinating systems for potential applications in quantum information processing and communication, since they can emit single photons and polarisation entangled photons pairs on demand. The asymmetry and inhomogeneity of real QDs has driven the development of a universal and fine post-growth tuning technique. In parallel, new growth methods are desired to create QDs with high emission efficiency and to control combinations of closely-spaced QDs, so-called "QD molecules" (QDMs). These systems are crucial for the realisation of a scalable information processing device after a tuning of their interaction energies. In this work, GaAs/AlGaAs QDs with low surface densities, high optical quality and widely tuneable emission wavelength are demonstrated, by infilling nanoholes fabricated by droplet etching epitaxy with different GaAs amounts. A tuning over a spectral range exceeding 10 meV is obtained by inducing strain in the dot layer. These results allow a fine tuning of the QD emission to the rubidium absorption lines, increasing the yield of single photons that can be used as hybrid semiconductor-atomic-interface. By embedding InGaAs/GaAs QDs into diode-like nanomembranes integrated onto piezoelectric actuators, the first device allowing the QD emission properties to be engineered by large electroelastic fields is presented. The two external fields reshape the QD electronic properties and allow the universal recovery of the QD symmetry and the generation of entangled photons, featuring the highest degree of entanglement reported to date for QD-based photon sources. A method for controlling the lateral QDM formation over randomly distributed nanoholes, created by droplet etching epitaxy, is demonstrated by depositing a thin GaAs buffer over the nanoholes. The effect on the nanohole occupancy of the growth parameters, such as InAs amount, substrate temperature and arsenic overpressure, is investigated as well. The QD pairs show good optical quality and selective etching post-growth is used for a better characterisation of the system. For the first time, the active tuning of the hole tunnelling rates in vertically aligned InGaAs/GaAs QDM is demonstrated, by the simultaneous application of electric and strain fields, optimising the device concept developed for the single QDs. This result is relevant for the creation and control of entangled states in optically active QDs. The modification of the electronic properties of QDMs, obtained by the combination of the two external fields, may enable controlled quantum operations.

This work summarizes properties of nitrogen containing GaAs, which are relevant for optoelectronic application and allow a deeper insight in the physics of this material. In the first part the dependence of the banggap energy of nitrogen implanted GaAs on several process parameters (implanted nitrogen concentration, implantation temperature, annealing duration and temperature) is investigated. The second part focuses on the relaxation dynamics of highly excited carriers. For this, the carrier relaxation dynamics in nitrogen implanted GaAs, in epitaxially grown GaAsN and in (pure) GaAs are investigated by means of pump probe measurements on a femtosecond time scale. The comparision of experimental results to calculated scattering rates leads to relevant informations of scattering mechanisms and electronic properties. / Diese Arbeit widmet sich Eigenschaften von Stickstoff-haltigem Gallium-Arsenid, die sowohl für das physikalische Verständnis als auch für optoelektronische Anwendungen dieses Materials relevant sind. Im ersten Teil dieser Arbeit wird die Abhängigkeit der Bandlücken-Energie von verschiedenen Prozess-Parametern (Stickstoffkonzentration, Implantationstemperatur, Ausheildauer und -temperatur) in Stickstoff-implantiertem GaAs untersucht. Der zweite Teil konzentriert sich auf die Relaxationsdynamik hoch angeregter Ladungsträger. Neben dem oben bereits angesprochenen Material wird in Anrege-Abfrage-Experimenten mit Femtosekunden-Zeitauflösung zusätzlich epitaktisch gewachsenes GaAsN und (Stickstoff-freies) GaAs untersucht. Die Berechnung der Streuraten und der Vergleich mit experimentell gewonnenen Daten liefert wesentliche Informationen über beteiligte Steumechanismen und elektronische Eigenschaften.

Semiconductor quantum dots (QDs) are fascinating systems for potential applications in quantum information processing and communication, since they can emit single photons and polarisation entangled photons pairs on demand. The asymmetry and inhomogeneity of real QDs has driven the development of a universal and fine post-growth tuning technique. In parallel, new growth methods are desired to create QDs with high emission efficiency and to control combinations of closely-spaced QDs, so-called "QD molecules" (QDMs). These systems are crucial for the realisation of a scalable information processing device after a tuning of their interaction energies. In this work, GaAs/AlGaAs QDs with low surface densities, high optical quality and widely tuneable emission wavelength are demonstrated, by infilling nanoholes fabricated by droplet etching epitaxy with different GaAs amounts. A tuning over a spectral range exceeding 10 meV is obtained by inducing strain in the dot layer. These results allow a fine tuning of the QD emission to the rubidium absorption lines, increasing the yield of single photons that can be used as hybrid semiconductor-atomic-interface. By embedding InGaAs/GaAs QDs into diode-like nanomembranes integrated onto piezoelectric actuators, the first device allowing the QD emission properties to be engineered by large electroelastic fields is presented. The two external fields reshape the QD electronic properties and allow the universal recovery of the QD symmetry and the generation of entangled photons, featuring the highest degree of entanglement reported to date for QD-based photon sources. A method for controlling the lateral QDM formation over randomly distributed nanoholes, created by droplet etching epitaxy, is demonstrated by depositing a thin GaAs buffer over the nanoholes. The effect on the nanohole occupancy of the growth parameters, such as InAs amount, substrate temperature and arsenic overpressure, is investigated as well. The QD pairs show good optical quality and selective etching post-growth is used for a better characterisation of the system. For the first time, the active tuning of the hole tunnelling rates in vertically aligned InGaAs/GaAs QDM is demonstrated, by the simultaneous application of electric and strain fields, optimising the device concept developed for the single QDs. This result is relevant for the creation and control of entangled states in optically active QDs. The modification of the electronic properties of QDMs, obtained by the combination of the two external fields, may enable controlled quantum operations.