Selective Spin Dewetting for Perovskite Solar Modules Fabricated on Engineered Au/ITO Substrates.

We introduce a novel method for fabricating perovskite solar modules using selective spin-coating on various Au/ITO patterned substrates. These patterns were engineered for two purposes: (1) to enhance selectivity of monolayers primarily self-assembling on the Au electrode, and (2) to enable seamless interconnection between cells through direct contact of the top electrode and the hydrophobic Au connection electrode. Utilizing SAMs-treated Au/ITO, we achieved sequential selective deposition of the electron transport layer (ETL) and the perovskite layer on the hydrophilic amino-terminated ITO, while the hole transport layer (HTL) was deposited on the hydrophobic CH3-terminated Au connection electrodes. Importantly, our approach had a negligible impact on the series resistance of the solar cells, as evidenced by the measured specific contact resistivity of the multilayers. A significant outcome was the production of a six-cell series-connected solar module with a notable average PCE of 8.32%, providing a viable alternative to the conventional laser scribing technique.

Ultra-low loss quantum photonic circuits integrated with single quantum emitters.

The scaling of many photonic quantum information processing systems is ultimately limited by the flux of quantum light throughout an integrated photonic circuit. Source brightness and waveguide loss set basic limits on the on-chip photon flux. While substantial progress has been made, separately, towards ultra-low loss chip-scale photonic circuits and high brightness single-photon sources, integration of these technologies has remained elusive. Here, we report the integration of a quantum emitter single-photon source with a wafer-scale, ultra-low loss silicon nitride photonic circuit. We demonstrate triggered and pure single-photon emission into a Si3N4 photonic circuit with ≈ 1 dB/m propagation loss at a wavelength of ≈ 930 nm. We also observe resonance fluorescence in the strong drive regime, showing promise towards coherent control of quantum emitters. These results are a step forward towards scaled chip-integrated photonic quantum information systems in which storing, time-demultiplexing or buffering of deterministically generated single-photons is critical.

SWIR imaging using PbS QD photodiode array sensors.

We fabricated a 1 × 10 PbS QD photodiode array with multiple stacked QD layers with high-resolution patterning using a customized photolithographic process. The array showed the average responsivity of 5.54 × 10-3 A/W and 1.20 × 10-2 A/W at 0 V and -1 V under 1310- nm short-wavelength infrared (SWIR) illumination. The standard deviation of the pixel responsivity was under 10%, confirming the uniformity of the fabrication process. The response time was 2.2 ± 0.13 ms, and the bandwidth was 159.1 Hz. A prototype 1310-nm SWIR imager demonstrated that the QD photodiode-based SWIR image sensor is a cost-effective and practical alternative for III-V SWIR image sensors.

Energy-Efficient III-V Tunnel FET-Based Synaptic Device with Enhanced Charge Trapping Ability Utilizing Both Hot Hole and Hot Electron Injections for Analog Neuromorphic Computing.

A charge trap device based on field-effect transistors (FET) is a promising candidate for artificial synapses because of its high reliability and mature fabrication technology. However, conventional MOSFET-based charge trap synapses require a strong stimulus for synaptic update because of their inefficient hot-carrier injection into the charge trapping layer, consequently causing a slow speed operation and large power consumption. Here, we propose a highly efficient charge trap synapse using III-V materials-based tunnel field-effect transistor (TFET). Our synaptic TFETs present superior subthreshold swing and improved charge trapping ability utilizing both carriers as charge trapping sources: hot holes created by impact ionization in the narrow bandgap InGaAs after being provided from the p+-source, and band-to-band tunneling hot electrons (BBHEs) generated at the abrupt p+n junctions in the TFETs. Thanks to these advances, our devices achieved outstanding efficiency in synaptic characteristics with a 5750 times faster synaptic update speed and 51 times lower sub-fJ/um2 energy consumption per single synaptic update in comparison to the MOSFET-based synapse. An artificial neural network (ANN) simulation also confirmed a high recognition accuracy of handwritten digits up to ∼90% in a multilayer perceptron neural network based on our synaptic devices.

Elliptical Polarization of Localized States in an Anisotropic Single GaAs Quantum Ring.

Localized states in an anisotropic single GaAs quantum ring were investigated in terms of polarization dependence of micro-photoluminescence spectrum at 5K. Given four Stokes parameters measured with a pair of linear polarizers and waveplates, the elliptical polarization states of two different vertical confinement states (k=1 and k=2) were compared with phase, rotation, and ellipticity angles. While the polarized emission intensity of the k=2 states becomes enhanced along [1,1,0] compared to that along [1,1¯,0], the polarization asymmetry of the k=1 states shows the opposite result. We conclude the polarization state is determined by the shape of the lateral wavefunctions. In the k=2 state, crescent-like wavefunctions are strongly localized, but the k=1 state consists of two crescent-like wavefunctions, which are connected weakly through quantum tunneling.

Threshold-based evolutionary magnitude estimation for an earthquake early warning system in the Sichuan-Yunnan region, China.

The Sichuan-Yunnan region is one of the most seismically vulnerable areas in China. Accordingly, an earthquake early warning (EEW) system for the region is essential to reduce future earthquake hazards. This research analyses the utility of two early warning parameters (τc and Pd) for magnitude estimation using 273 events that occurred in the Sichuan-Yunnan region during 2007-2015. We find that τc can more reliably predict high-magnitude events during a short P-wave time window (PTW) but produces greater uncertainty in the low-magnitude range, whereas Pd is highly correlated with the event magnitude depending on the selection of an appropriate PTW. Here, we propose a threshold-based evolutionary magnitude estimation method based on a specific combination of τc and Pd that both offers more robust advance magnitude estimates for large earthquakes and ensures the estimation accuracy for low-magnitude events. The advantages of the proposed approach are validated using data from 2016-2017 and the Ms 8.0 Wenchuan earthquake in an offline simulation. The proposed concept provides a useful basis for the future implementation of an EEW system in the Sichuan-Yunnan region.

On-demand spin-state manipulation of single-photon emission from quantum dot integrated with metasurface.

The semiconductor quantum dot (QD) has been successfully demonstrated as a potentially scalable and on-chip integration technology to generate the triggered photon streams that have many important applications in quantum information science. However, the randomicity of these photon streams emitted from the QD seriously compromises its use and especially hinders the on-demand manipulation of the spin states. Here, by accurately integrating a QD and its mirror image onto the two foci of a bifocal metalens, we demonstrate the on-demand generation and separation of the spin states of the emitted single photons. The photon streams with different spin states emitted from the QD can be flexibly manipulated to propagate along arbitrarily designed directions with high collimation of the smallest measured beaming divergence angle of 3.17°. Our work presents an effectively integrated quantum method for the simultaneously on-demand manipulation of the polarization, propagation, and collimation of the emitted photon streams.

Monolithic integration of visible GaAs and near-infrared InGaAs for multicolor photodetectors by using high-throughput epitaxial lift-off toward high-resolution imaging systems.

In this study, multicolor photodetectors (PDs) fabricated by using bulk p-i-n-based visible GaAs and near-infrared InGaAs structures were monolithically integrated through a high-throughput epitaxial lift-off (ELO) process. To perform multicolor detection in integrated structures, GaAs PDs were transferred onto InGaAs PDs by using a Y2O3 bonding layer to simultaneously detect visible and near-infrared photons and minimize the optical loss. As a result, it was found that the GaAs top PD and InGaAs bottom PD were vertically aligned without tilting in x-ray diffraction (XRD) measurement. A negligible change in the dark currents for each PD was observed in comparison with reference PDs through electrical characterization. Furthermore, through optical measurements and simulation, photoresponses were clearly revealed in the visible and near-infrared band for the material's absorption region, respectively. Finally, we demonstrated the simultaneous multicolor detection of the visible and near-infrared region,which implies individual access to each PD without mutual interference. These results are a significant improvement for the fabrication of multicolor PDs that enables the formation of bulk-based multicolor PDs on a single substrate with a high pixel density and nearly perfect vertical alignment for high-resolution multicolor imaging.

Nitrogen variations during the ice-on season in the eutrophic lakes.

Nitrogen accumulation in sediments, and the subsequent migration and transformations between sediment and the overlying water, plays an important role in the lake nitrogen cycle. However, knowledge of these processes are largely confined to ice-free seasons. Recent research under ice has mainly focused on the water eco-environmental effects during winter. Sediment N accumulation during the ice-on season and its associated eco-environmental impacts have never been systematically investigated. To address these knowledge gaps, we chose Wuliangsu Lake in China as a case study site, taking advantage of the spatial disparity between the 13 semi-separated sub-lakes. Based on samples of 35 sampling sites collected before, in the middle, and at the end of ice-on season separately, we performed a quantitative analysis of under-ice lake N accumulation and water-sediment N exchange by analyzing N fraction variations. Hierarchical Cluster Analysis and Relevance Analysis were used to help elucidate the main causes and implications of under-ice N variation. Our results clearly show that existing studies have underestimated the impact of under-ice N accumulation on the lake ecology throughout year: 1) Sediment N accumulated 2-3 times more than that before winter; 2) residual nitrogen (Res-N) contributed to the majority of the accumulated sediment N and was mainly induced by the debris of macrophytes; 3) total available nitrogen (TAN) was the most easily exchanged fractions between sediment and water, and it mainly affected the water environment during winter; 4) the Res-N accumulation during the ice-on season may have a strong impact on the eco-environment in the subsequent seasons. Our research is valuable for understanding the mechanism of internal nutrient cycle and controlling the internal nitrogen pollution, especially in shallow seasonally-frozen lakes that have long suffered from macrophyte-phytoplankton co-dominated eutrophication.

Light Controlled Optical Aharonov-Bohm Oscillations in a Single Quantum Ring.

We found that optical Aharonov-Bohm oscillations in a single GaAs/GaAlAs quantum ring can be controlled by excitation intensity. With a weak excitation intensity of 1.2 kW cm-2, the optical Aharonov-Bohm oscillation period of biexcitons was observed to be half that of excitons in accordance with the period expected for a two-exciton Wigner molecule. When the excitation intensity is increased by an order of magnitude (12 kW cm-2), a gradual deviation of the Wigner molecule condition occurs with decreased oscillation periods and diamagnetic coefficients for both excitons and biexcitons along with a spectral shift. These results suggest that the effective orbit radii and rim widths of electrons and holes in a single quantum ring can be modified by light intensity via photoexcited carriers, which are possibly trapped at interface defects resulting in a local electric field.

How do plants see the world? - UV imaging with a TiO2 nanowire array by artificial photosynthesis.

The concept of plant vision refers to the fact that plants are receptive to their visual environment, although the mechanism involved is quite distinct from the human visual system. The mechanism in plants is not well understood and has yet to be fully investigated. In this work, we have exploited the properties of TiO2 nanowires as a UV sensor to simulate the phenomenon of photosynthesis in order to come one step closer to understanding how plants see the world. To the best of our knowledge, this study is the first approach to emulate and depict plant vision. We have emulated the visual map perceived by plants with a single-pixel imaging system combined with a mechanical scanner. The image acquisition has been demonstrated for several electrolyte environments, in both transmissive and reflective configurations, in order to explore the different conditions in which plants perceive light.

Paths to light trapping in thin film GaAs solar cells.

It is now well established that light trapping is an essential element of thin film solar cell design. Numerous light trapping geometries have already been applied to thin film cells, especially to silicon-based devices. Less attention has been paid to light trapping in GaAs thin film cells, mainly because light trapping is considered less attractive due to the material's direct bandgap and the fact that GaAs suffers from strong surface recombination, which particularly affects etched nanostructures. Here, we study light trapping structures that are implemented in a high-bandgap material on the back of the GaAs active layer, thereby not perturbing the integrity of the GaAs active layer. We study photonic crystal and quasi-random nanostructures both by simulation and by experiment and find that the photonic crystal structures are superior because they exhibit fewer but stronger resonances that are better matched to the narrow wavelength range where GaAs benefits from light trapping. In fact, we show that a 1500 nm thick cell with photonic crystals achieves the same short circuit current as an unpatterned 4000 nm thick cell. These findings are significant because they afford a sizeable reduction in active layer thickness, and therefore a reduction in expensive epitaxial growth time and cost, yet without compromising performance.

Modulation of blood-brain barrier function by a heteroduplex oligonucleotide in vivo.

The blood-brain barrier (BBB) is increasingly regarded as a dynamic interface that adapts to the needs of the brain, responds to physiological changes, and gets affected by and can even promote diseases. Modulation of BBB function at the molecular level in vivo is beneficial for a variety of basic and clinical studies. Here we show that our heteroduplex oligonucleotide (HDO), composed of an antisense oligonucleotide and its complementary RNA, conjugated to α-tocopherol as a delivery ligand, efficiently reduced the expression of organic anion transporter 3 (OAT3) gene in brain microvascular endothelial cells in mice. This proof-of-concept study demonstrates that intravenous administration of chemically synthesized HDO can remarkably silence OAT3 at the mRNA and protein levels. We also demonstrated modulation of the efflux transport function of OAT3 at the BBB in vivo. HDO will serve as a novel platform technology to advance the biology and pathophysiology of the BBB in vivo, and will also open a new therapeutic field of gene silencing at the BBB for the treatment of various intractable neurological disorders.

Deterministic Integration of Quantum Dots into on-Chip Multimode Interference Beamsplitters Using in Situ Electron Beam Lithography.

The development of multinode quantum optical circuits has attracted great attention in recent years. In particular, interfacing quantum-light sources, gates, and detectors on a single chip is highly desirable for the realization of large networks. In this context, fabrication techniques that enable the deterministic integration of preselected quantum-light emitters into nanophotonic elements play a key role when moving forward to circuits containing multiple emitters. Here, we present the deterministic integration of an InAs quantum dot into a 50/50 multimode interference beamsplitter via in situ electron beam lithography. We demonstrate the combined emitter-gate interface functionality by measuring triggered single-photon emission on-chip with g(2)(0) = 0.13 ± 0.02. Due to its high patterning resolution as well as spectral and spatial control, in situ electron beam lithography allows for integration of preselected quantum emitters into complex photonic systems. Being a scalable single-step approach, it paves the way toward multinode, fully integrated quantum photonic chips.

Room temperature operation of mid-infrared InAs0.81Sb0.19 based photovoltaic detectors with an In0.2Al0.8Sb barrier layer grown on GaAs substrates.

In this paper, InAs0.81Sb0.19-based hetero-junction photovoltaic detector (HJPD) with an In0.2Al0.8Sb barrier layer was grown on GaAs substrates. By using technology computer aided design (TCAD), a design of a barrier layer that can achieve nearly zero valance band offsets was accomplished. A high quality InAs0.81Sb0.19 epitaxial layer was obtained with relatively low threading dislocation density (TDD), calculated from a high-resolution X-ray diffraction (XRD) measurement. This layer showed a Hall mobility of 15,000 cm2/V⋅s, which is the highest mobility among InAsSb layers with an Sb composition of around 20% grown on GaAs substrates. Temperature dependence of dark current, photocurrent response and responsivity were measured and analyzed for fabricated HJPD. HJPD showed the clear photocurrent response having a long cutoff wavelength of 5.35 µm at room temperature. It was observed that the dark current of HJPDs is dominated by the diffusion limited current at temperatures ranging from 200K to room temperature from the dark current analysis. Peak responsivity of HJPDs exhibited the 1.18 A/W and 15 mA/W for 83K and a room temperature under zero bias condition even without anti-reflection coating (ARC). From these results, we believe that HJPDs could be an appropriate PD device for future compact and low power dissipation mid-infrared on-chip sensors and imaging devices.

Electrical properties and thermal stability in stack structure of HfO2/Al2O3/InSb by atomic layer deposition.

Changes in the electrical properties and thermal stability of HfO2 grown on Al2O3-passivated InSb by atomic layer deposition (ALD) were investigated. The deposited HfO2 on InSb at a temperature of 200 °C was in an amorphous phase with low interfacial defect states. During post-deposition annealing (PDA) at 400 °C, In-Sb bonding was dissociated and diffusion through HfO2 occurred. The diffusion of indium atoms from the InSb substrate into the HfO2 increased during PDA at 400 °C. Most of the diffused atoms reacted with oxygen in the overall HfO2 layer, which degraded the capacitance equivalent thickness (CET). However, since a 1-nm-thick Al2O3 passivation layer on the InSb substrate effectively reduced the diffusion of indium atoms, we could significantly improve the thermal stability of the capacitor. In addition, we could dramatically reduce the gate leakage current by the Al2O3 passivation layer. Even if the border traps measured by C-V data were slightly larger than those of the as-grown sample without the passivation layer, the interface trap density was reduced by the Al2O3 passivation layer. As a result, the passivation layer effectively improved the thermal stability of the capacitor and reduced the interface trap density, compared with the sample without the passivation layer.

Al2O3 Passivation Effect in HfO2·Al2O3 Laminate Structures Grown on InP Substrates.

The passivation effect of an Al2O3 layer on the electrical properties was investigated in HfO2-Al2O3 laminate structures grown on indium phosphide (InP) substrate by atomic-layer deposition. The chemical state obtained using high-resolution X-ray photoelectron spectroscopy showed that interfacial reactions were dependent on the presence of the Al2O3 passivation layer and its sequence in the HfO2-Al2O3 laminate structures. Because of the interfacial reaction, the Al2O3/HfO2/Al2O3 structure showed the best electrical characteristics. The top Al2O3 layer suppressed the interdiffusion of oxidizing species into the HfO2 films, whereas the bottom Al2O3 layer blocked the outdiffusion of In and P atoms. As a result, the formation of In-O bonds was more effectively suppressed in the Al2O3/HfO2/Al2O3/InP structure than that in the HfO2-on-InP system. Moreover, conductance data revealed that the Al2O3 layer on InP reduces the midgap traps to 2.6 × 1012 eV-1 cm-2 (compared to that of HfO2/InP, that is, 5.4 × 1012 eV-1 cm-2). The suppression of gap states caused by the outdiffusion of In atoms significantly controls the degradation of capacitors caused by leakage current through the stacked oxide layers.

Structural and Electrical Properties of EOT HfO2 (<1 nm) Grown on InAs by Atomic Layer Deposition and Its Thermal Stability.

We report on changes in the structural, interfacial, and electrical characteristics of sub-1 nm equivalent oxide thickness (EOT) HfO2 grown on InAs by atomic layer deposition. When the HfO2 film was deposited on an InAs substrate at a temperature of 300 °C, the HfO2 was in an amorphous phase with an sharp interface, an EOT of 0.9 nm, and low preexisting interfacial defect states. During post deposition annealing (PDA) at 600 °C, the HfO2 was transformed from an amorphous to a single crystalline orthorhombic phase, which minimizes the interfacial lattice mismatch below 0.8%. Accordingly, the HfO2 dielectric after the PDA had a dielectric constant of ∼24 because of the permittivity of the well-ordered orthorhombic HfO2 structure. Moreover, border traps were reduced by half than the as-grown sample due to a reduction in bulk defects in HfO2 dielectric during the PDA. However, in terms of other electrical properties, the characteristics of the PDA-treated sample were degraded compared to the as-grown sample, with EOT values of 1.0 nm and larger interfacial defect states (Dit) above 1 × 10(14) cm(-2) eV(-1). X-ray photoelectron spectroscopy data indicated that the diffusion of In atoms from the InAs substrate into the HfO2 dielectric during the PDA at 600 °C resulted in the development of substantial midgap states.

Observation of a Biexciton Wigner Molecule by Fractional Optical Aharonov-Bohm Oscillations in a Single Quantum Ring.

The Aharonov-Bohm effect in ring structures in the presence of electronic correlation and disorder is an open issue. We report novel oscillations of a strongly correlated exciton pair, similar to a Wigner molecule, in a single nanoquantum ring, where the emission energy changes abruptly at the transition magnetic field with a fractional oscillation period compared to that of the exciton, a so-called fractional optical Aharonov-Bohm oscillation. We have also observed modulated optical Aharonov-Bohm oscillations of an electron-hole pair and an anticrossing of the photoluminescence spectrum at the transition magnetic field, which are associated with disorder effects such as localization, built-in electric field, and impurities.

Polarized Terahertz Waves Emitted from In0.2Ga0.8As Nanowires.

We investigate the polarizability of terahertz (THz) waves emitted from undoped In0.2Ga0.8As nanowires (NWs). THz emission amplitude shows strong enhancement in vertically aligned NWs compared to less-aligned NWs. In particular, polarized THz waves are clearly demonstrated in aligned NWs via a drastic variation of amplitudes as a function of the axis angle in polarization-sensitive photoconductive antenna. In addition, phase reversal between aligned and less-aligned NWs substantiates the geometrical dependence of electronic diffusion in generating the transient THz electric fields.