Meta-photonics: a bridge between physical association and digital models in photonics

1.Design details for different models and optical experiments 2.Schematic diagram of metasurface structure 3.Schematic diagram of forward design effect 4.Inverse Design of structural parameters with respect to amplitude 5.Materials and Method

Multiheterojunction Phototransistors Based on Graphene–PbSe Quantum Dot Hybrids

Graphene-semiconductor quantum dot (QD) hybrid field effect phototransistors (FEpTs) have attracted much interest due to their ultrahigh gain and responsivity in photo detection. However, most reported results are based on single-layer heterojunction, and the multiheterojunction FEpTs are often ignored. Here, we design two typical multiheterojunction FEpTs based on graphene–PbSe quantum dot (QD) hybrids, including QD at the bottom layer (QD-bottom) and graphene at the bottom layer (G-bottom) FEpTs. Through a comparative study, G-bottom FEpTs showed a multisaturation behavior due to the multigraphene layer effect, which was absent in the QD-bottom FEpTs. The mobilities for electrons and holes were μ_E = 147 cm² V^–1 s^–1 and μ_E = 137 cm² V^–1 s^–1 in the G-bottom FEpTs and μ_E = 14 cm² V^–1 s^–1 and μ_E = 59 cm² V^–1 s^–1 in the QD-bottom FEpTs. Higher responsivity (∼10⁶ A W^–1) and faster response rate were both achieved by the G-bottom FEpTs. All of the advantages in G-bottom FEpTs were attributed to the back-gate effect. Therefore, high performance is expected in those FEpTs whose heterojunctions are designed to be close to the back-gate

PbS-Decorated WS₂ Phototransistors with Fast Response

Tungsten disulfide (WS₂), as a typical metal dichalcogenides (TMDs), has aroused keen research interests in photodetection. Here, field effect phototransistors (FE_pTs) based on heterojunction between monolayer WS₂ and PbS colloidal quantum dots are demonstrated to show high photoresponsivity (up to ∼14 A/W), wide electric bandwidth (∼396 Hz), and excellent stability. Meanwhile, the devices exhibit fast photoresponse times of ∼153 μs (rise time) and ∼226 μs (fall time) due to the assistance of heterojunction on the transfer of photoexcitons. Therefore, excellent device performances strongly underscore monolayer WS₂–PbS quantum dot as a promising material for future photoelectronic applications

Ambipolar Quantum-Dot-Based Low-Voltage Nonvolatile Memory with Double Floating Gates

Considerable research efforts have been devoted to promoting memory performance, especially the memory window and retention time. In this work, we develop an innovative field-effect-transistor memory with graphene oxide (GO)/gold nanoparticles (Au NPs) as double floating gates (DFG) and PbS quantum dots (QDs) as the semiconductor layer. QDs can provide both electrons and holes in the channel, which offers a chance for the floating gates to trap both of them to achieve bidirectional threshold voltage shifts after programming and erasing operations. Due to the DFG structure covering the GO sheets on the Au NP monolayer, the enhanced memory window (∼2.72 V at a programming/erasing voltage of ±10 V) can be attributed to more charge carriers being trapped in the floating gates. More importantly, because of the different energy levels between GO and Au NPs, the DFG construction brings about an energy barrier that prevents the trapped charges from leaking back to the channel, so that the retention capability is significantly improved. The outstanding memory performance will give the QD-based DFG memory great potential to have its own place in the flash memory market

Broadband Phototransistor Based on CH₃NH₃PbI₃ Perovskite and PbSe Quantum Dot Heterojunction

Organic lead halide perovskites have received a huge amount of interest since emergence, because of tremendous potential applications in optoelectronic devices. Here field effect phototransistors (FE_pTs) based on CH₃NH₃PbI₃ perovskite/PbSe colloidal quantum dot heterostructure are demonstrated. The high light absorption and optoelectric conversion efficiency, due to the combination of perovskite and quantum dots, maintain the responsivities in a high level, especially at 460 nm up to 1.2 A/W. The phototransistor exhibits bipolar behaviors, and the carrier mobilities are determined to be 0.147 cm²V^–1s^–1 for holes and 0.16 cm²V^–1s^–1 for electrons. The device has a wide spectral response spectrum ranging from 300 to 1500 nm. A short photoresponse time is less than 3 ms due to the assistance of heterojunction on the transfer of photoexcitons. The excellent performances presented in the device especially emphasize the CH₃NH₃PbI₃ perovskite–PbSe quantum dot as a promising material for future photoelectronic applications