Novel ultraviolet scintillators based on semiconductor quantum dot emitters for significantly enhanced photodetection and photovoltaics

Abstract

Silicon photonics opens opportunities to realize optoelectronic devices directly on large-scale integrated electronics, leveraging advanced Si fabrication and computation capabilities. However, silicon is constrained in different aspects for use in optoelectronics. Such one limitation is observed in Si based photodetectors, cameras, and solar cells that exhibit very poor responsivity in the ultraviolet (UV) spectral range. Si CMOS photodetectors and CCD cameras cannot be operated in UV, despite the strong demand for UV detection and imaging in security applications. Also, although 95% of the photovoltaics market is dominated by Si based solar cells, silicon is not capable of using UV radiation of the solar spectrum for solar energy conversion, as required especially in space applications. In this thesis for the first time, we demonstrate novel UV scintillators made of semiconductor quantum dot emitters hybridized on Si detectors and cameras to detect and image in UV with significantly improved responsivity and on Si solar cells to generate electrical energy from UV radiation with significantly improved solar conversion efficiency. We present the device conception, design, fabrication, experimental characterization, and theoretical analysis of these UV nanocrystal scintillators. Integrating highly luminescent CdSe/ZnS core-shell nanocrystals, we demonstrate hybrid photodetectors that exhibit two-orders-of-magnitude peak enhancement in their responsivity. We also develop photovoltaic nanocrystal scintillators to enhance open-circuit voltage, short-circuit current, fill factor, and solar conversion efficiency in UV. Hybridizing CdSe/ZnS quantum dots on Si photovoltaic devices, we show that the solar conversion efficiency is doubled under white light illumination (Xe lamp). Such UV scintillator nanocrystals hold great promise to enable photodetection and imaging in UV and extend photovoltaic activity to UV.