Colloidal semiconductor quantum dots/graphene (QD/Gr) heterojunction nanohybrids have recently emerged as a promising candidate for broadband photodetection. The QD/Gr nanohybrids are quantum sensors that take advantages of the quantum confinement in QDs for spectral tunability and that in graphene for superior charge mobility, leading high photoconductive gains. Therefore, the QD/Gr nanohybrids allows design of broadband photodetectors and the intrinsic high gain could lead to high detectivity (D*). This presentation reports the result in a recent research on QD/Gr nanohybrids for short-wave to middle-wave infrared (SWIR-MWIR) detectors. The focus of the study is to identify key performance limiting factors on responsivity, D* and response speed through an understanding of the underlying physics. Specifically, we have investigated the origin of the noise in the QD/Gr and found the intrinsic quantum limit of the noise could be achieved by tuning the Fermi energy of the graphene. Furthermore, the charge transfer between QD and graphene, which impacts the responsivity and response speed, has been found to be dictated by the QD surface states and QD/Gr interface. Through development of atomic-scale surface and interface engineering approaches to reduce or eliminate charge traps, efficient charge transfer across the QD/Gr interface can be achieved, leading to high uncooled D* at SWIR-MWIR wavelengths at room temperature approaching that of the cooled counterparts. This result illustrates the QD/Gr nanohybrids could provide a promising low-cost, scalable scheme for uncooled infrared detection and imaging.
Colloidal semiconductor quantum dots/graphene van der Waals (vdW) heterojunctions take advantages of the enhanced light-matter interaction and spectral tenability of quantum dots (QDs) and superior charge mobility in graphene, providing a promising alternative for uncooled infrared photodetectors with a gain or external quantum efficiency up to 1010. In these QD/graphene vdW heterostructures, the QD/graphene interface plays a critical role in controlling the optoelectronic process including exciton dissociation, charge injection and transport. Specifically, charge traps at the vdW interface can increase the noise, reduce the responsivity and response speed. This paper highlight our recent progress in engineering the vdW heterojunction interface towards more efficient charge transfer for higher photoresponsivity, D* and response speed. These results illustrate that the importance in vdW heterojunction interface engineering in QD/graphene photodetectors which may provide a promising pathway for low-cost, printable and flexible infrared detectors and imaging systems.
Heterojunction nanohybrids based on low-dimension semiconductors, including colloidal quantum dots (QDs) and 2D atomic materials (graphene, transition metal chalcogenides, etc) provide a fascinating platform to design of new photonic and optoelectronic devices that take advantages of the enhanced light-solid interaction attributed to their strong quantum confinement and superior charge mobility for uncooled photodetectors with a high gain up to 1010. In these heterojunction nanohybrids, the van der Waals (vdW) interface plays a critical role in controlling the optoelectronic process including exciton dissociation by the interface built-in field that drives the follow-up charge injection and transport to graphene. In this paper, we present our recent progress in development of such heterostructures nanohybrids for uncooled infrared detectors including PbS and FeS2 QDs/graphene and 2D vdW heterostructures MoTe2/Graphene/SnS2 and GaTe/InSe. We have found that nonstoichiometric Fe1–xS2 QDs (x = 0.01–0.107) with strong localized surface plasmonic resonance (LSPR) can have much enhanced absorption in broadband from ultraviolet to short-wave infrared (SWIR, 1–3 μm). Consequently, the LSPR Fe1–xS2 QDs/graphene heterostructure photodetectors exhibit extraordinary photoresponsivity in exceeding 4.32 ×106 A/W and figure-of-merit detectivity D* < 7.50 ×1012 Jones in the broadband of UV–Vis–SWIR at room temperature. The 2D vdW heterostructures allows novel designs of interface band alignments with uncooled NIR-SWIR D* up to 1012 Jones. These results illustrate that the heterostructure nanohybrids provide a promising pathway for low-cost, printable and flexible infrared detectors and imaging systems.
Low-dimensional carbon nanostructures such as nanotubes (CNTs) and graphene have excellent electronic,
optoelectronic and mechanical properties, which provide fresh opportunities for designs of optoelectronic devices of
extraordinary performance in addition to the benefits of low cost, large abundance, and light weight. This work
investigates photodetectors made with CNTs and graphene with a particular focus on carbon-based nanohybrids aiming
at a nanoscale control of photon absorption, exciton dissociation and charge transfer. Through several examples
including graphene/GaSe-nanosheets, graphene/aligned ZnO nanorods, SWCNT/P3HT, and SWCNT/biomolecule, we
show an atomic-scale control on the interfacial heterojunctions is the key to high responsivity and fast photoresponse in
these nanohybrids optoelectronic devices.
Carbon-based nanostructures including nanotubes (CNTs) and graphene have superior electronic, optoelectronic and mechanical properties, which provide fresh opportunities for designs of novel devices of extraordinary performance in addition to the benefits of low cost, large abundance, and light weight. In this work, a comparative study of two types of uncooled infrared detectors based single-wall as well as multi-wall CNTs and their hybrids with graphene or polymer is presented. One is bolometer in which excitons dissociate via interactions with the phonons on the CNTs. The other implements built-in voltage at the hybrid interface between CNTs and graphene (or polymer) to assist exciton dissociation for photoconductivity. The difference in exciton dissociation has been found to directly affect the device performance such as responsivity and detectivity. This investigation aims at understanding the fundamental physics governing exciton dissociation and charge as well as phonon transport at nanoscales and its impact on the device performance in these CNT-based infrared detectors.
Pb(Zr,Ti)O3 (PZT), a promising material for uncooled infrared detection, is an anisotropic perovskite with the best pyroelectric effect observed along the c-axis. Although c-axis orientated PZT films can be easily obtained on single crystal substrates with minimal lattice mismatch, it remains a challenge in practical cases when they must be grown on non-textured polymer based sacrificial coatings over Si substrates. To address this issue, we have been focused on development of thin textured MgO templates on non-textured substrates, such as amorphous SiO2/Si and polymer coated SiO2/Si, using an ion-beam-assisted deposition (IBAD) technique. C-axis-oriented multi-layered LaNiO3/Pb(Zr,Ti)O3/LaNiO3 have been achieved and the ferroelectric properties, that impact the figure of merit for IR sensors, have been characterized.
We have been focused on growth of multi-layered LaNiO3/Pb(Zr,Ti)O3/LaNiO3 on bare Si and polymer-coated Si substrates for infrared detector applications. A unique ion-beam assisted pulsed laser deposition (IBAD-PLD) has been employed to address two critical issues related to these thin film ferroelectric (TFFE) devices: to reduce the thermal budget and to enhance the texture of the devices. IBAD has been a well-known technique for deposition of thin films due to the ability to control morphology, adhesion, texture, and stoichiometry of the film by providing extra kinetic energies to, and to generate desired textures in films by preferential sputtering of the growing surface of the film. We have studied the role of several processing parameters of IBAD-PLD process, including ion-beam energy, current density, IBAD time, and substrate temperature in order to identify the best processing window for LaNiO3/Pb(Zr,Ti)O3/LaNiO3.
A novel cation-exchange process has been developed for synthesis of bulks and epitaxy of thin films of highly volatile Hg-based high- temperature superconductors (Hg-HTS's). Unlike in a conventional thermal reaction process, precursor matrices of Tl-based high- temperature superconductors were employed in the cation exchange process and annealed in Hg vapors, in which Tl cations were perturbed thermally and replaced subsequently by the Hg cations. A large processing window has been observed suitable for such an atomic perturbation process. This allows Hg-HTS's to inherit high- quality crystalline structures, surface and film/substrate interface morphologies from their Tl-HTS's precursor matrices, eliminating difficulties in synthesis and epitaxy of Hg-HTS's associated with the high volatility of Hg-related compounds. Nearly pure phase HgBa2CaCu2O6+(delta ) and HgBa2Ca2Cu3O8+(delta )bulks and epitaxial thin films were obtained reproducibly with exciting physical properties including high Tc's, high Jc's, and low microwave surface resistance. This cation-exchange technique may also provide a general scheme for synthesis of other volatile compounds with pre-designed structure and composition.
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