Suchergebnisse

Broadband infrared photodetectors have profound importance in diverse applications including security, gas sensing, bioimaging, spectroscopy for food quality, and recycling, just to name a few. Yet, these applications can currently be served by expensive epitaxially grown photodetectors, limiting their market potential and social impact. The use of colloidal quantum dots (CQDs) and 2D materials in a hybrid layout is an attractive alternative to design low-cost complementary metal-oxide-semiconductor (CMOS) compatible infrared photodetectors. However, the spectral sensitivity of these conventional hybrid detectors is restricted to 2.1 µm. Herein, a hybrid structure comprising molybdenum disulfide (MoS2) with lead selenide (PbSe) CQDs is presented to extend their sensitivity further toward the mid-wave infrared, up to 3 µm. A room-temperature responsivity of 137.6 A/W and a detectivity of 7.7 × 10^10 Jones are achieved at 2.55 µm owing to highly efficient photoexcited carrier separation at the interface of MoS2 and PbSe in combination with an oxide coating to reduce dark current; the highest value is yet for a PbSe-based hybrid device. These findings strongly support the successful fabrication of hybrid devices, which may pave the pathway for cost-effective, high-performance, next-generation, novel photodetectors. ; The authors acknowledge financial support from the European Research Council (ERC) under the European Union's Horizon 2020 research (grant agreement no. 725165) as well as Graphene Flagship under Grant Agreement Nr. 881603 (Core3). The authors also acknowledge financial support from the Spanish Ministry of Economy and Competitiveness (MINECO), and the "Fondo Europeo de Desarrollo Regional" (FEDER) through grant TEC2017-88655-R, from the Spanish State Research Agency through the "Severo Ochoa" program for Centers of Excellence in R&D (CEX2019-000910-S), from Fundació Cellex, Fundació Mir-Puig, and from Generalitat de Catalunya through the CERCA program. ; Peer Reviewed ; Postprint (author's final draft)

Steady-state access to intraband transitions in colloidal quantum dots (CQDs), via heavy doping, allows exploiting the electromagnetic spectrum at energies below the band gap. CQD intraband optoelectronics opens up a new path to cheap mid- and long-wavelength infrared photodetectors and light-emitting devices, which today employ mostly epitaxial materials. As a recent field of experimental research, thorough studies of the basic properties of intraband transitions in CQDs are still lacking. In this work, we investigate the size and temperature dependence of the intraband transition in heavily n-doped PbS quantum dot (QD) films. We measure the absorption coefficient of the intraband transition to be in the order of $10^4$ cm$^{-1}$, which is comparable to the value of the interband absorption coefficient. Additionally, we determine the size-dependence of the oscillator strength of the intraband transition. We demonstrate a negative dependence of the intraband energy with temperature, in contrast to the positive dependence of the interband transition. ; We thank Dr. Iacopo Torre for helpful discussions. The authors acknowledge financial support from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement no. 725165), the Spanish Ministry of Economy and Competitiveness (MINECO), and the "Fondo Europeo de Desarrollo Regional" (FEDER) through grant TEC2017-88655-R. The authors also acknowledge financial support from Fundacio Privada Cellex, the program CERCA and from the Spanish Ministry of Economy and Competitiveness, through the "Severo Ochoa" Program for Centres of Excellence ; Peer Reviewed ; Postprint (published version)

Optical sensing in the mid- and long-wave infrared (MWIR, LWIR) is of paramount importance for a large spectrum of applications including environmental monitoring, gas sensing, hazard detection, food and product manufacturing inspection, and so forth. Yet, such applications to date are served by costly and complex epitaxially grown HgCdTe quantum-well and quantum-dot infrared photodetectors. The possibility of exploiting low-energy intraband transitions make colloidal quantum dots (CQD) an attractive low-cost alternative to expensive low bandgap materials for infrared applications. Unfortunately, fabrication of quantum dots exhibiting intraband absorption is technologically constrained by the requirement of controlled heavy doping, which has limited, so far, MWIR and LWIR CQD detectors to mercury-based materials. Here, we demonstrate intraband absorption and photodetection in heavily doped PbS colloidal quantum dots in the 5-9 µm range, beyond the PbS bulk band gap, with responsivities on the order of 10-4 A/W at 80 K. We have further developed a model based on quantum transport equations to understand the impact of electron population of the conduction band in the performance of intraband photodetectors and offer guidelines toward further performance improvement. ; I.R. acknowledges support from the Ministerio de Economiá , Industria y Competitividad of Spain via a Juan de la Cierva fellowship. The authors acknowledge financial support from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (Grant Agreement 725165), the Spanish Ministry of Economy and Competitiveness (MINECO), and the "Fondo Europeo de Desarrollo Regional" (FEDER) through Grant TEC2017- 88655-R. The authors also acknowledge financial support from Fundacio Privada Cellex, the program CERCA and from the Spanish Ministry of Economy and Competitiveness, through the "Severo Ochoa" Programme for Centres of Excellence in R&D (SEV-2015-0522). S.C. acknowledge support from a Marie Curie Standard European Fellowship ("NAROBAND", H2020-MSCA-IF-2016-750600). ; Peer Reviewed ; Postprint (published version)

Defects play an important role in tailoring the optoelectronic properties of materials. Here we demonstrate that sulphur vacancies are able to engineer sub-band photoresponse into the short-wave infrared range due to formation of in-gap states in Bi2S3 single crystals supported by density functional (DF) calculations. Sulfurization and subsequent refill of the vacancies results in faster response but limits the spectral range to the near infrared as determined by the bandgap of Bi2S3. A facile chemical treatment is then explored to accelerate the speed of sulphur deficient (SD)-based detectors on the order of 10 ms without sacrificing its spectral coverage into the infrared, while holding a high D* close to 10^15 Jones in the visible-near infrared range and 10^12 Jones at 1.6 um. This work also provides new insights into the role sulphur vacancies play on the electronic structure and, as a result, into sub-bandgap photoresponse enabling ultrasensitive, fast and broadband photodetectors. ; The authors acknowledge financial support from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement no. 725165), the Spanish Ministry of Economy and Competitiveness (MINECO), and the "Fondo Europeo de Desarrollo Regional" (FEDER) through grant TEC2017-88655-R. The authors also acknowledge financial support from Fundacio Privada Cellex, the program CERCA and from the Spanish Ministry of Economy and Competitiveness, through the "Severo Ochoa" Programme for Centres of Excellence in R&D (SEV-2015-0522). Y.Y. acknowledges support from the National Natural Science Foundation of China under grant no. 61805045. S.C. acknowledges support from Marie Curie Standard European Fellowship ("NAROBAND", H2020-MSCA-IF-2016-750600). Furthermore, the research leading to these results has received funding from the European Union H2020 Programme under grant agreement no. 785219 Graphene Flagship ; Peer reviewed

Materials with optical gain in the infrared are of paramount importance for optical communications, medical diagnostics, and silicon photonics. The current technology is based either on costly III-V semiconductors that are not monolithic to silicon CMOS technology or Er-doped fiber technology that does not make use of the full fiber transparency window. Colloidal quantum dots (CQDs) offer a unique opportunity as an optical gain medium in view of their tunable bandgap, solution processability, and CMOS compatibility. The 8-fold degeneracy of infrared CQDs based on Pb-chalcogenides has hindered the demonstration of low-threshold optical gain and lasing, at room temperature. We demonstrate room-temperature, infrared, size-tunable, band-edge stimulated emission with a line width of ~14 meV. Leveraging robust electronic doping and charge-exciton interactions in PbS CQD thin films, we reach a gain threshold at the single exciton regime representing a 4-fold reduction from the theoretical limit of an 8-fold degenerate system, with a net modal gain in excess of 100 cm-1. ; The authors acknowledge financial support from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement no. 725165), the Spanish Ministry of Economy and Competitiveness (MINECO), and the 'Fondo Europeo de Desarrollo Regional' (FEDER) through grant TEC2017- 88655-R. The authors also acknowledge financial support from Fundacio Privada Cellex, the program CERCA, and from the Spanish Ministry of Economy and Competitiveness through the "Severo Ochoa" Programme for Centres of Excellence in R&D (SEV-2015-0522). S.C. acknowledges support from a Marie Curie Standard European Fellowship (NAROBAND, H2020-MSCA-IF-2016-750600). I.R. acknowledges support from the Ministerio de Economiá , Industria y Competitividad of Spain via a Juan de la Cierva fellowship. We are also thankful to Dr. Kaifen Wu for fruitful discussions. ; Peer Reviewed ; Postprint (published version)

Indium tin oxide (ITO) is the most widely used transparent conductor in applications such as light emitting diodes, liquid crystal devices, touch screens, and photovoltaic cells. So far, its use has mainly been limited to the visible range (380 nm–750 nm), as it reflects at longer wavelengths and, consequently, its transmission is low. Here, we introduce a simple technique, based on high temperature annealing, which can reduce reflection in the near-infrared range (750 nm–2400 nm). With an optimized set of parameters, we were able to modulate the ITO properties and achieve a high transmission, greater than 80% including substrate contribution, at telecommunication wavelengths (C-band, 1530 nm–1565 nm) while still maintaining high electrical conductivity (resistivity <1.9 × 10−4 Ω cm). By using the newly developed infrared ITO transparent conductor, we demonstrate quantum dot solar cells with 27.7% enhancement in external quantum efficiency at the first exciton peak (1650 nm), and liquid crystal switching devices with 25% enhancement in transmission, with respect to device counterparts incorporating commercially available ITO. ; We acknowledge financial support from the Spanish Ministry of Economy and Competitiveness through Grant No. MAT2017-85232-R (AEI/FEDER, EU) and the Spanish State Research Agency through the "Severo Ochoa" program for Centers of Excellence in R&D (CEX2019-000910-S and CEX2019-000917 S), and project TUNA-SURF (Grant No. PID2019-106892RB-I00), from Fundació Cellex, Fundació Mir-Puig and from Generalitat de Catalunya through the CERCA program through AGAUR Grant Nos. 2017 SGR 1634 and 2017 301 SGR1377. C.G. acknowledges the funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement No. 713729. This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement No. 754510. Y.C. acknowledges the China Scholarship Council (Grant No. 201506890029). The authors also acknowledge Vittoria Finazzi for her help and fruitful discussions. ; Peer reviewed