Abstract
Lead sulfide (PbS) quantum dots (QDs) have great potential in optoelectronic applications because of their desirable characteristics as a light absorber for near-infrared (NIR) photodetection. However, most PbS-based NIR photodetectors are two-terminal devices, which require an integrated pixel circuit to be practical photosensors. Here we report on PbS QD/indium gallium zinc oxide (InGaZnO, IGZO) metal oxide semiconductor hybrid phototransistors with a photodetection capability between 700 and 1400 nm, a range that neither conventional Si nor InGaAs photodetectors can cover. The new hybrid phototransistor exhibits excellent photoresponsivity of over 106 A W−1 and a specific detectivity in the order of 1013 Jones for NIR (1000 nm) light. Furthermore, we demonstrate an NIR (1300 nm) imager using photogating inverter pixels based on PbS/IGZO phototransistors at an imaging frequency of 1 Hz with a high output voltage photogain of ~4.9 V (~99%). To the best of our knowledge, this report demonstrates the first QD/metal oxide hybrid phototransistor-based flat panel NIR imager. Our hybrid approach using QD/metal oxide paves the way for the development of gate-tunable and highly sensitive flat panel NIR sensors/imagers that can be easily integrated. A hybrid near-infrared photoinverter based on lead sulphide quantum (PbS) dots and InGaZnO that exhibits a high photogain has been made. PbS quantum dots have promising properties for near-infrared detection, but two-terminal devices based on them require an integrated pixel circuit. Now, Do Kyung Hwang at Korea University of Science and Technology and co-workers have demonstrated a hybrid near-infrared detector that employs PbS quantum dots to sensitize InGaZnO. The detector covers a wavelength range of 700–1,400 nanometres, which is not covered by conventional photodetectors. It also exhibits an excellent photoresponsivity of over 106 amperes per watt. The researchers consider that this approach will open up the way to develop highly sensitive, flat-panel near-infrared sensors and imagers that are both gate tunable and readily integrable. We propose hybrid approach of two classes of PbS QD as NIR light absorber and IGZO as the photogenerated charges acceptor/transport semiconductor to create phototransistor for near infrared (NIR) detection/imaging. Such hybrid phototransistor shows photodetection capability between 700 and 1400 nm. We demonstrate a NIR (1300 nm) imager using photogating inverter pixel based on PbS/IGZO hybrid phototransistor.
Highlights
PbS quantum dots (QDs) sensitized IGZO hybrid phototransistor was fabricated through a facile spin-coating process, in which colloidal PbS QDs were formed on the top of prefabricated IGZO thin-film transistors (TFTs) arrays on glass substrates
This CYTOP film was used as a passivation layer because the PbS QD capped with the EDT ligand is vulnerable to degradation in ambient air
In order to calculate the noise equivalent power (NEP) and the specific detectivity (D*), the noise power spectral densities were measured with an SR 570 lownoise-current preamplifier (Stanford Research System (SRS), Sunnyvale, CA, USA) and an Advantest R9211B digital spectrum analyzer (Advantest Corporation, Tokyo, Japan)
Summary
Over the past several years, various chalcogenide or metal oxide colloidal quantum dots (QDs) have been synthesized and developed for optoelectronic device applications such as light emitting diodes,[1,2,3,4] photodetectors[5,6,7,8,9,10,11,12] and photovoltaic cells.[13,14,15,16,17,18] Among the various types of QDs, lead sulfide (PbS) QD has been extensively studied because it is a promising material for collecting sunlight energy[14,15] or for near-infrared (NIR) photodetection.[8,19] Recently, the commercial interest in NIR detection has been growing due to the potential for various imaging applications including optical tomography for biological investigations, process monitoring and night vision.[19]. PbS QD sensitized IGZO hybrid phototransistor was fabricated through a facile spin-coating process, in which colloidal PbS QDs were formed on the top of prefabricated IGZO TFT arrays on glass substrates. An amorphous fluoropolymer CYTOP (Asahi Glass, Tokyo, Japan, 100 nm) film was deposited on the top of the devices by spin coating at 2000 r.p.m. for 60 s and annealed at 100 °C for 20 min in a nitrogen-filled glove box. This CYTOP film was used as a passivation layer because the PbS QD capped with the EDT ligand is vulnerable to degradation in ambient air. In order to calculate the noise equivalent power (NEP) and the specific detectivity (D*), the noise power spectral densities were measured with an SR 570 lownoise-current preamplifier (Stanford Research System (SRS), Sunnyvale, CA, USA) and an Advantest R9211B digital spectrum analyzer (Advantest Corporation, Tokyo, Japan)
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