Morötesinde önemli ölçüde fotoalgılama ve fotovoltaik iyileştirmesi için yarıiletken kuvantum nokta ışıyıcıları temelli yenilikçi sintilatörler

ABSTRACTNOVEL ULTRAVIOLET SCINTILLATORS BASED ONSEMICONDUCTOR QUANTUM DOT EMITTERSFOR SIGNIFICANTLY ENHANCEDPHOTODETECTION AND PHOTOVOLTAICSEvren MutlugünM.S. in PhysicsSupervisor: Assist. Prof. Dr. Hilmi Volkan DemirAugust 2007Silicon photonics opens opportunities to realize optoelectronic devices directly on large-scale integrated electronics, leveraging advanced Si fabrication and computationcapabilities. However, silicon is constrained in different aspects for use inoptoelectronics. Such one limitation is observed in Si based photodetectors, cameras, andsolar cells that exhibit very poor responsivity in the ultraviolet (UV) spectral range. SiCMOS photodetectors and CCD cameras cannot be operated in UV, despite the strongdemand for UV detection and imaging in security applications. Also, although 95% of thephotovoltaics market is dominated by Si based solar cells, silicon is not capable of usingUV radiation of the solar spectrum for solar energy conversion, as required especially inspace applications. In this thesis for the first time, we demonstrate novel UV scintillatorsmade of semiconductor quantum dot emitters hybridized on Si detectors and cameras todetect and image in UV with significantly improved responsivity and on Si solar cells togenerate electrical energy from UV radiation with significantly improved solarconversion efficiency. We present the device conception, design, fabrication,experimental characterization, and theoretical analysis of these UV nanocrystalscintillators. Integrating highly luminescent CdSe/ZnS core-shell nanocrystals, wedemonstrate hybrid photodetectors that exhibit two-orders-of-magnitude peakenhancement in their responsivity. We also develop photovoltaic nanocrystal scintillatorsto enhance open-circuit voltage, short-circuit current, fill factor, and solar conversionefficiency in UV. Hybridizing CdSe/ZnS quantum dots on Si photovoltaic devices, weshow that the solar conversion efficiency is doubled under white light illumination (Xelamp). Such UV scintillator nanocrystals hold great promise to enable photodetectionand imaging in UV and extend photovoltaic activity to UV.Keywords: Nanocrystals, quantum dots, scintillators, Si, photodetectors, cameras,photovoltaics, solar cells, photocurrent, responsivity, solar conversion efficiency,ultraviolet.