光神经网络中的半导体光电器件

叙述了光神经网络的基本概念，并介绍了光神经网络中使用中的半导体光电器件， 体可调制光电检测器（ＶＳＰＤ），具有内存贮光神经芯片，人工视网膜芯片，以及不对称的Ｆａｂｒｙ－Ｐｅｒｏｔ调制器（ＡＦＰＭ）的最新研究结果。     

Effect of edges on the reliability of GaAs and (AlGa) as heterojunction leds

The effect of various diode geometries on the degradation rate of heterojunction diodes with either GaAs or (AlGa)As in the recombination region has been studied. It is shown that GaAs diodes are particularly sensitive to edge-related degradation which varies with the current density J as J^3/2. The addition of Al to the recombination region considerably reduces the degradation rate of diodes both with and without exposed edges, and data are reported for Al_0.1Ga_0.9As stripe-contact edge-emitting structures operating for over 20,000 hours with no change in output at 1000 A/cm².     

Carbon Quantum Dots with Near-Unity Quantum Yield Bandgap Emission for Electroluminescent Light-Emitting Diodes

Carbon quantum dots (CQDs) feature bright and tunable photoluminescence, solution processability, and low toxicity, showing great potential in optoelectronics. However, the large-scale synthesis of CQDs with near-unity photoluminescence quantum yield (PLQY) has not been achieved so far. In this study, we perform radical-assisted synthesis of hexagon-shaped CQDs (H-CQDs) delivering near-unity PLQY (96 %). Experimental and theoretical analyses revealed that the large vertically oriented transition dipole moment of H-CQDs originating from high symmetry results in nearly 100 % PLQY. The H-CQDs also exhibited a high electron mobility of up to 0.07 cm² V⁻¹ s⁻¹. These properties enable the H-CQD-based light-emitting diodes with a high external quantum efficiency of 4.6 % and a record maximum brightness of over 11 000 cd m⁻². This study represents a significant advance that CQDs-based electroluminescent device can be utilized for potential display and lighting applications.     

Narrowband Fluorescent Emitters Based on BN-Doped Polycyclic Aromatic Hydrocarbons for Efficient and Stable Organic Light-Emitting Diodes

Organic light-emitting diodes (OLEDs) using conventional fluorescent emitters are currently attracting considerable interests due to outstanding stability and abundant raw materials. To construct high-performance narrowband fluorophores to satisfy requirements of ultra-high-definition displays, a strategy fusing multi-resonance BN-doped moieties to naphthalene is proposed to construct two novel narrowband fluorophores. Green Na−sBN and red Na−dBN, manifest narrow full-width at half-maxima of 31 nm, near-unity photoluminescence quantum yields and molecular horizontal dipole ratios above 90 %. Their OLEDs exhibit the state-of-the-art performances including high external quantum efficiencies (EQE), ultra-low efficiency roll-off and long operational lifetimes. The Na−sBN-based device achieves EQE as high as 28.8 % and remains 19.8 % even at luminance of 100,000 cd m⁻², and Na−dBN-based device acquires a record-high EQE of 25.2 % among all red OLEDs using pure fluorescent emitters.     

A Simple Molecular Design Strategy for Pure-Red Multiple Resonance Emitters

Though the flourishment of materials with multiple resonance (MR) in blue to green regions, red-emissive MR emitters are still rare in literatures, which definitely should be resolved for further applications. Herein, we report a simple molecular design strategy for the construction of pure-red MR emitters by conjugate charge transfer, which could greatly enhance the π-conjugation degree and charge-transfer property of the target molecule while maintaining the basic feature of MR, leading to a significant redshift of more than 128 nm compared to the selected parent MR core. The proof-of-concept emitter PPZ-BN exhibited a pure-red emission with a dominant peak at 613 nm and a small full-width-at-half-maximum of 0.16 eV (48 nm). The optimized organic light-emitting diode showed a high external quantum efficiency of 26.9 %, a small efficiency roll-off, and an excellent operation stability (LT99) of more than 43 hours at an initial luminance of 10 000 cd m⁻².     

Precise Regulation of Emission Maxima and Construction of Highly Efficient Electroluminescent Materials with High Color Purity

Advanced multiple resonance induced thermally activated delayed fluorescence (MR-TADF) emitters have emerged as a privileged motif for applications in organic light-emitting diodes (OLEDs), because they furnish highly tunable TADF characteristics and high color purity emission. Herein, based on the unique nitrogen-atom embedding molecular engineering (NEME) strategy, a series of compounds BN-TP-Nx (x=1, 2, 3, 4) have been customized. The nitrogen-atom anchored at different position of triphenylene hexagonal lattice entails varying degrees of perturbation to the electronic structure. The newly-constructed emitters have demonstrated the precise regulation of emission maxima of MR-TADF emitters to meet the actual industrial demand, and further enormously enriched the MR-TADF molecular reservoir. The BN-TP-N3-based OLED exhibits ultrapure green emission, with peak of 524 nm, full-width at half-maximum (FWHM) of 33 nm, Commission Internationale de L'Eclairage (CIE) coordinates of (0.23, 0.71), and maximum external quantum efficiency (EQE) of 37.3 %.     

Introducing Spiro-locks into the Nitrogen/Carbonyl System towards Efficient Narrowband Deep-blue Multi-resonance TADF Emitters

The current availability of multi-resonance thermally activated delayed fluorescence (MR-TADF) materials with excellent color purity and high device efficiency in the deep-blue region is appealing. To address this issue in the emerged nitrogen/carbonyl MR-TADF system, we propose a spiro-lock strategy. By incorporating spiro functionalization into a concise molecular skeleton, a series of emitters (SFQ, SOQ, SSQ, and SSeQ) can enhance molecular rigidity, blue-shift the emission peak, narrow the emission band, increase the photoluminescence quantum yield by over 92 %, and suppress intermolecular interactions in the film state. The referent CZQ without spiro structure has a more planar skeleton, and its bluer emission in the solution state redshifts over 40 nm with serious spectrum broadening and a low PLQY in the film state. As a result, SSQ achieves an external quantum efficiency of 25.5 % with a peak at 456 nm and a small full width at half maximum of 31 nm in a simple unsensitized device, significantly outperforming CZQ. This work discloses the importance of spiro-junction in modulating deep-blue MR-TADF emitters.     

Water-Driven Synthesis of Deep-Blue Perovskite Colloidal Quantum Wells for Electroluminescent Devices

Perovskite colloidal quantum wells (QWs) are promising to realize narrow deep-blue emission, but the poor optical performance and stability suppress their practical application. Here, we creatively propose a water-driven synthesis strategy to obtain size-homogenized and strongly confined deep-blue CsPbBr₃ QWs, corresponding to three monolayers, which emit at the deep-blue wavelength of 456 nm. The water controls the orientation and distribution of the ligands on the surface of the nanocrystals, thus inducing orientated growth through the Ostwald ripening process by phagocytizing unstable nanocrystals to form well-crystallized QWs. These QWs present remarkable stability and high photoluminescence quantum yield of 94 %. Furthermore, we have prepared light-emitting diodes based on the QWs via the all-solution fabrication strategy, achieving an external quantum efficiency of 1 % and luminance of 2946 cd m⁻², demonstrating state-of-the-art brightness for perovskite QW-based LEDs.     

Solution-Processable Pure-Red Multiple Resonance-induced Thermally Activated Delayed Fluorescence Emitter for Organic Light-Emitting Diode with External Quantum Efficiency over 20 %

Developing solution-processable red organic light-emitting diodes (OLEDs) with high color purity and efficiency based on multiple resonance thermally activated delayed fluorescence (MR-TADF) is a formidable challenge. Herein, by introducing auxiliary electron donor and acceptor moieties into the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) distributed positions of multiple resonance skeleton simultaneously, an effective strategy to obtain red MR-TADF emitters was represented. The proof-of-the-concept molecule BN-R exhibits a narrowband pure-red emission at 624 nm, with a high luminous efficiency of 94 % and a narrow bandwidth of 46 nm. Notably, the fabricated solution-processable pure-red OLED based on BN-R exhibits a state-of-the-art external quantum efficiency over 20 % with the Commission Internationale de I’Éclairage coordinates of (0.663, 0.337) and a long operational lifetime (LT₅₀) of 1088 hours at an initial luminance of 1000 cd m⁻².     

Optimization, design and fabrication of a non-cryogenic quantum infrared detector

A study of the optimization of the detectivity of a mid infrared double heterostructure photovoltaic detector is proposed. Simple approximate analytic expressions for the dark current are compared with full numerical calculations, and give physical insight on the mechanisms dominating the dark current. The analysis is performed step by step, from a simple p–n junction to the full double heterostructure. The influence of temperature, barrier band gap energy in a double heterostructure, doping density in the active region, on diffusion and generation–recombination mechanisms is analyzed. It is shown how the performances of a double heterostructure photovoltaic detector can be improved by a controlled doping the active region. Nevertheless, its development is still limited by the difficulties occurring during device processing. For example, the use of dry etching for the processing of InAs_0.91Sb_0.09 p–i–n photovoltaic detectors induces a strong leakage current along the mesa edge. In this letter, we show an improvement of the R₀A characteristic by several orders of magnitude at low temperature by using an Ion Beam Etching (IBE) followed by a wet chemical etching. This optimized and reliable device processing allows us to demonstrate that the detector performance is actually limited by the diffusion current of holes. Finally, we discuss the ability of an n-type barrier made of InAs/AlSb super-lattice to avoid hole diffusion and to improve the R₀A characteristic of these detectors. To cite this article: B. Vinter et al., C. R. Physique 4 (2003).