3,003 research outputs found
Solution processed quantum dot photodetectors
To find sustainable solutions for the production of energy, it is necessary to create
photovoltaic technologies that make every photon count. To pursue this necessity, in
the present work photodetectors of zinc oxide embedded with nano-structured materials,
that significantly raise the conversion of solar energy to electric energy, were developed.
The novelty of this work is on the development of processing methodologies in which
all steps are in solution: quantum dots synthesis, passivation of their surface and sol-gel
deposition.
The quantum dot solutions with different capping agents were characterized by UVvisible
absorption spectroscopy, spectrofluorimetry, dynamic light scattering and transmission
electron microscopy. The obtained quantum dots have dimensions between 2
and 3nm. These particles were suspended in zinc acetate solutions and used to produce
doped zinc oxide films with embedded quantum dots, whose electric response was tested.
The produced nano-structured zinc oxide materials have a superior performance than
the bulk, in terms of the produced photo-current. This indicates that an intermediate
band material should have been produced that acts as a photovoltaic medium for solar
cells. The results are currently being compiled in a scientific article, that is being
prepared for possible submission to Energy and Environmental Science or Nanoscale
journals
Thin-film quantum dot photodiode for monolithic infrared image sensors
Imaging in the infrared wavelength range has been fundamental in scientific, military and surveillance applications. Currently, it is a crucial enabler of new industries such as autonomous mobility (for obstacle detection), augmented reality (for eye tracking) and biometrics. Ubiquitous deployment of infrared cameras (on a scale similar to visible cameras) is however prevented by high manufacturing cost and low resolution related to the need of using image sensors based on flip-chip hybridization. One way to enable monolithic integration is by replacing expensive, small-scale III-V-based detector chips with narrow bandgap thin-films compatible with 8- and 12-inch full-wafer processing. This work describes a CMOS-compatible pixel stack based on lead sulfide quantum dots (PbS QD) with tunable absorption peak. Photodiode with a 150-nm thick absorber in an inverted architecture shows dark current of 10(-6) A/cm(2) at 2 V reverse bias and EQE above 20% at 1440 nm wavelength. Optical modeling for top illumination architecture can improve the contact transparency to 70%. Additional cooling (193 K) can improve the sensitivity to 60 dB. This stack can be integrated on a CMOS ROIC, enabling order-of-magnitude cost reduction for infrared sensors
Photo-FETs: phototransistors enabled by 2D and 0D nanomaterials
The large diversity of applications in our daily lives that rely on photodetection technology requires photodetectors with distinct properties. The choice of an adequate photodetecting system depends on its application, where aspects such as spectral selectivity, speed, and sensitivity play a critical role. High-sensitivity photodetection covering a large spectral range from the UV to IR is dominated by photodiodes. To overcome existing limitations in sensitivity and cost of state-of-the-art systems, new device architectures and material systems are needed with low-cost fabrication and high performance. Low-dimensional nanomaterials (0D, 1D, 2D) are promising candidates with many unique electrical and optical properties and additional functionalities such as flexibility and transparency. In this Perspective, the physical mechanism of photo-FETs (field-effect transistors) is described and recent advances in the field of low-dimensional photo-FETs and hybrids thereof are discussed. Several requirements for the channel material are addressed in view of the photon absorption and carrier transport process, and a fundamental trade-off between them is pointed out for single-material-based devices. We further clarify how hybrid devices, consisting of an ultrathin channel sensitized with strongly absorbing semiconductors, can circumvent these limitations and lead to a new generation of highly sensitive photodetectors. Recent advances in the development of sensitized low-dimensional photo-FETs are discussed, and several promising future directions for their application in high-sensitivity photodetection are proposed.Peer ReviewedPostprint (author's final draft
Strategies for controlled electronic doping of colloidal quantum dots
Over the last several years tremendous progressed progress has been made in incorporating
Colloidal Quantum Dots (CQDs) as photoactive components in optoelectronic devices. A
significant part of that progress is associated with significant advancements made in
achievingon controlled electronic doping of the CQDs and thus improving the electronic
properties of CQDs solids. Today, a variety of strategies exists towards that purpose and this
minireview aims at surveying major published works in this subject. Additional attention is
given to the many challenges associated with the task of doping CQDs as well as to the
optoelectronic functionalities and applications being realized when successfully achieving light
and heavy electronic doping of CQDs.Peer ReviewedPostprint (author's final draft
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