Nitridische Halbleiter-Nanostrukturen als optisch auslesbare Sensoren
| Autor: | Heinz, Dominik José |
|---|---|
| Přispěvatelé: | Scholz, Ferdinand, Christiansen, Silke |
| Jazyk: | němčina |
| Rok vydání: | 2020 |
| Předmět: |
DDC 540 / Chemistry & allied sciences
Selektive Epitaxie Chemischer Sensor Galliumnitrid Condensed Matter::Other Gassensor Physics::Optics Gas detectors Condensed Matter::Mesoscopic Systems and Quantum Hall Effect Condensed Matter::Materials Science Quantenwell ddc:540 Photonischer Kristall Photolumineszenz MOCVD-Verfahren Nanostruktur Biosensor |
| Popis: | An optochemical sensor concept is presented based on the transducing properties of near-surface indium gallium nitride quantum wells. In contrast to the established electrical read-out in chemical sensing, the photoluminescence response of group III-nitride quantum wells is applied as transducer signal. Oxidative and reductive adsorbates are studied with respect to their influence on spectrum and intensity of the quantum well photoluminescence. Indium gallium nitride quantum wells are positioned within the space charge region caused by the Fermi-level pinning at the semiconductor surface. Pronounced adsorbate-caused spectral shifts of the photoluminescence are observed which are attributed to changes of the near-surface electric field. Respectively, the quantum-confined Stark effect can be applied as transducer signal with sensitivity to the local electric field. A pronounced blue shift and a reduction of the photoluminescence intensity is observed in presence of oxygen for polar quantum wells. It is presumed that oxygen increases the near-surface band bending and weakens the internal piezo fields in these structures. Hence, the spectral blue shift of the photoluminescence can be attributed to a reduction of the quantum-confined Stark effect. In contrast, a spectral red shift is observed in presence of atomic hydrogen with a thin layer of platinum acting as a catalyst on the gallium nitride surface. Atomic hydrogen is found to reduce the near-surface band bending which corresponds to an increased quantum-confined Stark effect in polar quantum wells. The sensitivity of the transducers strongly depends on the chemical pre-treatment and oxidative state of the surface. Strongest sensitivity for oxygen is observed directly after thermal annealing. In order to enable local variations of ambient gases on the surface, an integration of the optical transducers in a microfluidic sensor structure is demonstrated. Transparent microfluidic channels are realized on the surface of polar indium gallium nitride quantum well structures using optical lithography. A reduction of the quantum well photoluminescence is observed and a tendency for a spectral blue shift in presence of oxygen. Additionally, semi-polar and non-polar quantum wells are investigated with respect to their spectral photoluminescence response to adsorbates. The spectral photoluminescence response is found to be strongly dependent on the polarity of the quantum wells. Adsorbate-caused spectral shifts of the photoluminescence are most pronounced for polar quantum wells with strong piezo fields present inside the quantum wells. The intrinsic piezoelectric field is expected to cause a strong pre-tilt of the polar quantum well band structure which leads to a higher sensitivity for variations of the externally induced electric field. Spectral shifts of the photoluminescence up to 25 meV are found for polar quantum wells in presence of oxygen. In comparison, reduced spectral shifts of less than 10 meV are observed for semi-polar structures, and almost vanishing spectral sensitivity for non-polar structures. Due to their high spectral sensitivity, polar quantum wells are considered as promising candidates for sensor structures based on the quantum-confined Stark effect. Optical biosensing is demonstrated using such polar indium gallium nitride quantum well structures. First investigations are performed with the iron storage molecule ferritin which exists with varying iron-load. Ferritin and apoferritin (corresponds to ferritin without iron-load) molecules are immobilized on the sensor surface. A significant spectral photoluminescence shift is found depending on the iron-load of the molecules. In presence of apoferritin a spectral red shift of approximately 13 meV is observed compared to the reference surface. In contrast, only a minor spectral blue shift of less than 2 meV is found for ferritin. Polar indium gallium nitride quantum wells are found to enable a new approach for sensing ferritin-bound iron as a potential biomarker in medical applications. |
| Databáze: | OpenAIRE |
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