Effects Of Device Structure Research Articles

Investigation into fill factor and open-circuit voltage degradations in silicon heterojunction solar cells under accelerated life testing at elevated temperatures

There are many reports on open-circuit voltage (VOC) degradation but limited reports on fill factor (FF) degradation in silicon heterojunction (SHJ) solar cells which are either subjected to an accelerated testing condition or to a field condition. The factors contributing to FF loss and VOC loss due to aging required a thorough investigation to gain insight into potential loss mechanisms and the approaches to mitigate them. In this context, we subjected SHJ solar cells of the same structure to varying accelerated testing conditions (i.e. exposure temperature of 90 °C versus 120 °C, under 1-sun illumination) in experiment 1 to 3 of this work. The SHJ cells exposed to a temperature of 90 °C were nearly stable in performance even after 2000 h while those exposed to 120 °C degraded significantly in FF. Device measurements and analysis revealed that the FF degradation was due to an increase in series resistance (Rs) and hole collection barrier. In experiment 4, the effect of device structure was investigated by subjecting cells with only front-side indium tin oxide (ITO) and those with both-sides ITO to the same accelerated testing conditions at a temperature of 90 °C under 1-sun illumination. The result obtained revealed that SHJ cells with both sides ITO were nearly stable in electrical performance while those with only front ITO degraded in performance, dominated by VOC loss. The VOC loss was perhaps due to loss of passivation at the rear-side of the cells.

Scaling of voltage controlled magnetic anisotropy based skyrmion memory and its neuromorphic application

Voltage controlled skyrmion memory requires less energy compared to current controlled method where voltage changes magnetic anisotropy (VCMA) and Dzyaloshinskii-Moriya interaction (DMI). Ferromagnetic (FM) and synthetic antiferromagnetic (SAFM) memory devices are simulated using electric field control method where gate and gap width are chosen as smaller than skyrmion size so that skyrmion can feel the change in voltage polarity in the neighbouring gate and moves accordingly. Scaling of memory device is performed which shows SAFM memory can be made much narrower compared to FM memory as skyrmion diameter also depends on width of the structure. Effects of device structure and skyrmion-skyrmion repulsion force on skyrmion diameter variation are shown in cylindrical structure considering effect of demagnetizing field. Apart from these, neuromorphic application is considered where skyrmion moves from central square neuron region to surrounding synapse region or vice versa by the application of voltage. Switching time, voltage range, energy and scaling of device dimensions are shown for synapse-neuron having different number of skyrmions where multiple skyrmions represent different weight in the neuromorphic circuit.

Effect of device structure on signal measurement of zinc oxide nanocolumn-based resonant cavity hydrophones

Hydrophones with three different resonant cavities (microscope slide, cavity with 9.8 mm diameter and 5.7 mm[Formula: see text] curve surface, and cavity with 14 mm diameter and 6.5 mm[Formula: see text] curve surface) and with two different electrode structures (interdigital electrode, without the interdigital electrode but with top–bottom structure) were designed and fabricated. Zinc oxide (ZnO) film was deposited on indium–tin oxide/glass as seed layer and ZnO nanocolumns were grown as the piezoelectric material. Grown ZnO nanocolumns were used in all samples as the sound receiver of all designed hydrophones to enhance the sensing effect and efficiency of fabricated hydrophones. The electrode mask was then adhered on the surfaces of ZnO nanocolumns to complete the electrodes of designed resonant cavity. While measuring the hydrophones without interdigitated electrode, the measurement probes were contacted directly on the substrate and on the top layer of the material. Finally, the resonant cavities in all designed hydrophones were encapsulated using epoxy resin to finish the package of the fabricated hydrophones, and then the sound receiving performance of the hydrophones was evaluated in the water and the results were well compared in this study.

Device topological thermal management of β-Ga2O3 Schottky barrier diodes* *Project supported by the National Natural Science Foundation of China (Grant Nos. 61925110, 61821091, 62004184, 62004186, and 51961145110), the National Key R&D Program of China (Grant Nos. 2018YFB0406504 and 2016YFA0201803), the Strategic Priority Research Program of the Chinese Academy of Sciences (CAS) (Grant No. XDB44000000), the Key Research Program of Frontier

The ultra-wide bandgap semiconductor β gallium oxide (β-Ga2O3) gives promise to low conduction loss and high power for electronic devices. However, due to the natural poor thermal conductivity of β-Ga2O3, their power devices suffer from serious self-heating effect. To overcome this problem, we emphasize on the effect of device structure on peak temperature in β-Ga2O3 Schottky barrier diodes (SBDs) using TCAD simulation and experiment. The SBD topologies including crystal orientation of β-Ga2O3, work function of Schottky metal, anode area, and thickness, were simulated in TCAD, showing that the thickness of β-Ga2O3 plays a key role in reducing the peak temperature of diodes. Hence, we fabricated β-Ga2O3 SBDs with three different thickness epitaxial layers and five different thickness substrates. The surface temperature of the diodes was measured using an infrared thermal imaging camera. The experimental results are consistent with the simulation results. Thus, our results provide a new thermal management strategy for high power β-Ga2O3 diode.

Effects of device structure on thermo-optic switch and design optimization

The study on reliability of multi-layer structure of thermo-optic switch under thermal mechanical coupling effect is the basic research subject in modern micro-optoelectronics. Power consumption and response time are the most important performance indexes. Based on the generalized thermoelasticity theory, thermo-optic switch models of various structures are built to simulate the temperature and stress field for structure optimization. The numerical results show that an appropriate cross-section shape can reduce the switch power consumption without prejudice to the response speed, the refractive index of the core layer varies with the temperature, and the inter-layer thermal mismatching stress of the double-ridge structure is the maximum. The above findings will introduce new ideas for research and development and design of new optic switches.

Effect of device structure on the resistive switching characteristics of organic polymers fabricated through all printed technology

Developments in organic bi-stable non-volatile memory devices have shown that organic materials are essential for the next generation of electrical memory unit owing to their low cost, high flexibility and large scalability. This study depicts an important aspect of organic memory devices by observing the effect of changing device structure on its switching characteristics. Memory devices with a bilayer and bulk-heterojunction structure were fabricated through an all printed technology by utilizing two organic polymers such as MEH: PPV and PMMA. Silver (Ag) was selected as the top and bottom electrode due to its high conductivity and easy processing. Though identical polymers were used in both device structures, but interestingly change in structure caused change in properties. It was observed that bilayer structure had much higher switching ratio and stability against various biasing cycles as compared to its bulk-heterojunction counterpart. Superior switching characteristics of bilayer structure were due to the presence of a well-defined interface between both polymers. Bulk-heterojunction device suffers the drawback of phase separation in a single organic layer between the two polymers.

The effects of device structure on the performances of distyrylbiphenyl compounds based organic light emitting diodes

The effects of device structure and applied current density on the performances of blue organic light emitting diodes based on unsymmetrical distyrylbiphenyl compounds were investigated. According to the attached functional groups on the unsymmetrical distyrylbiphenyls, two kinds of compounds were synthesized and evaluated: (Z)-4-(2-p-tolylvinyl)-4′-[1-phenyl-2-(4-tert-butylphenyl)vinyl]biphenyl (U-DSB_tBM) and (Z)-4-[2-(4-tert-butylphenyl)vinyl]-4′-[1-phenyl-2-(4-tert-butylphenyl)vinyl]biphenyl (U-DSB_tBtB). As the emission layers of U-DSB_tBM or U-DSB_tBtB thickened, the operation voltage increased and the emitted light became more blue. After inserting a hole blocking layer, the values of the Commission Internationale de l’Eclairage (CIE) chromaticity coordinates were (0.14–0.21, 0.15–0.28). As the applied current increased, the y coordinate of the sample using U-DSB_tBM increased; however, that of the sample using U-DSB_tBtB decreased regardless of the device structure. The X-ray diffraction data and the atomic force microscopy imaging results suggest that the hole mobility of U-DSB_tBM is greater than that of U-DSB_tBtB, indicating that the recombination region is located in U-DSB_tBM at a low current, and that it expands to the electron transport layer at a high current. Therefore, the device structure and mobility affect device performance, and both factors should be considered to optimize the device properties.

The simulation of temperature dependence of responsivity and response time for 6H-SiC UV photodetector

In this paper the temperature dependence of responsivity and response time for 6H-SiC ultraviolet (UV) photodetector is simulated based on numerical model in the range from 300 K to 900 K. The simulation results show that the responsivity and the response time of device are less sensitive to temperature and this kind of UV photodetector has excellent temperature stability. Also the effects of device structure and bias voltage on the responsivity and the response time are presented. The thicker the drift region is, the higher the responsivity and the longer the response time are. So the thickness of drift region has to be carefully designed to make trade-off between responsivity and response time.

Orange Electroluminescence from a Divalent Europium Complex

Divalent molecular lanthanide complexes are shown to offer promise as tunable light emitting materials in thin film electroluminescent displays for the first time in this study. Bright orange luminescence is obtained from thin film EL device structures containing bis[tris(dimethylpyrazolyl)borate]europium(II) (1), which has a high quantum efficiency in the solid state. The effect of device structure upon device efficiency and light purity is discussed and an optimum EL device structure for 1 detailed.

Theoretical analysis and experimental research on the finline ferrite isolator (abstract)

Recently, the finline ferrite devices have attracted people’s attention. Beyer et al. have done theoretical and experimental researches for a finline isolator.1,2 In order to make it convenient for theoretical design and experimental adjustment of this device, we have developed a synthetical theory and have carried out the experimental research successfully.3 In this paper, we have done the further theoretical analysis and experimental researches for the finline ferrite isolator, such as the impedance matching, the effects of device structure on performances, and the transplantation of a waveguide isolator to a finline isolator problem. Good agreement between design and experiment is obtained. The performances of a X-band finline isolator are as follows A+<1.5 dB, A−≳18 dB, VSWR<1.5 in a 8% bandwidth, and the bia-field is lower (about 1000 Oe).<ks>