<p>Spin filtering properties of novel GaNAs alloys are reported in this thesis. Spin-dependent recombination (SDR) in GaNAs via a deep paramagnetic defect center is intensively studied.  By using the optical orientation photoluminescence (PL) technique, GaNAs is shown to be able to spin filter electrons injected from GaAs, which is a useful functional property for integratition with future electronic devices.  The spin filtering ability is found to degrade in narrow GaNAs quantum well (QW) structures which is attributed to (i) acceleration of band-to-band recombination competing with the SDR process and to (ii) faster electron spin relaxation in the narrow QWs.  Ga interstitial-related defect centers have been found to be responsible for the SDR process by using the optically detected magnetic resonance (ODMR) technique. The defects are found to be the dominant grown-in defects in GaNAs, commonly formed during both MBE and MOCVD growths.  Methods to control the concentration of the Ga interstitials by varying doping, growth parameters and post-growth treatments are also examined.</p>

Spin filtering properties of novel GaNAs alloys are reported in this thesis. Spin-dependent recombination (SDR) in GaNAs via a deep paramagnetic defect center is intensively studied.  By using the optical orientation photoluminescence (PL) technique, GaNAs is shown to be able to spin filter electrons injected from GaAs, which is a useful functional property for integratition with future electronic devices.  The spin filtering ability is found to degrade in narrow GaNAs quantum well (QW) structures which is attributed to (i) acceleration of band-to-band recombination competing with the SDR process and to (ii) faster electron spin relaxation in the narrow QWs.  Ga interstitial-related defect centers have been found to be responsible for the SDR process by using the optically detected magnetic resonance (ODMR) technique. The defects are found to be the dominant grown-in defects in GaNAs, commonly formed during both MBE and MOCVD growths.  Methods to control the concentration of the Ga interstitials by varying doping, growth parameters and post-growth treatments are also examined.

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.

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.

Nontraditional college student enrollment in the United States is rapidly growing and is predicted to continue to increase. Similarly, female students are currently the majority student population on college campuses. Although numerous studies document college student experiences, few focus on first-generation Latinas who are student-mothers at community colleges. The purpose of this study was to explore the educational experiences of first-generation Latina nontraditional student-mothers enrolled at a community college in California to identify the ways in which grit (ganas) and mindsets influenced their success. This inquiry followed Moustakas’s (1994) transcendental phenomenology research process. Individual interviews of five Latinas were analyzed using Moustakas’s modification of the Van Kaam method of analysis. The findings indicate that each woman had a similar yet unique story based upon their intersectional identities and the space in which they lived in at the time of this study. These stories collectively echoed a phenomenon rooted in cultural pervasiveness and generational continuity, an urgency to break cultural norms, and the grasp on ganas and mindsets that each participant held onto while striving to reach their educational goals. The participants’ stories illuminated an unanticipated connection to my own story as a Latina student-mother in search of a higher education. This connection provided me with a deeper understanding of my educational path and the realization that ganas and mindsets also influenced my educational experiences. The implications from this study offer ways to support this specific group of students both collectively and individually. La inscripción de estudiantes del colegio no tradicionales en los Estados Unidos está creciendo rápidamente y se prevé que continúe aumentando. Del mismo modo, las alumnas son actualmente la población estudiantil mayoritaria en los colegios. Aunque numerosos estudios documentan experiencias de estudiantes de colegio, pocos se centran en latinas de primera generación que son estudiantes-madres en colegios comunitarios. El propósito de este estudio fue explorar las experiencias educativas de las madres Latinas que son estudiantes no tradicionales de primera generación inscritas en un colegio comunitario en California para identificar las maneras en que sus ganas y mentalidades influyeron en su éxito. Este estudio siguió al proceso de investigación de fenomenología trascendental de Moustakas (1994). Las entrevistas individuales de cinco Latinas fueron analizadas utilizando la modificación de Moustakas del método de análisis de Van Kaam. Los hallazgos indican que cada mujer tenía una historia similar pero única basada en sus identidades interseccionales y el espacio en el que vivían en el momento de este estudio. Estas historias hicieron eco colectivamente de un fenómeno arraigado en la omnipresencia cultural y la continuidad generacional, la urgencia de romper las normas culturales y la comprensión de las ganas y las mentalidades que cada participante aferró mientras se esforzaba por alcanzar sus metas educativas. Las historias de los participantes iluminaron una conexión imprevista con mi propia historia como estudiante-madre Latina en busca de una educación superior. Esta conexión me proporcionó una comprensión más profunda de mi camino educativo y la comprensión de que las ganas y las mentalidades también influyeron en mis experiencias educativas. Las implicaciones de este estudio ofrecen maneras de apoyar a este grupo específico de estudiantes tanto colectiva como individualmente.