The role of the Ge mole fraction in improving the performance of a nanoscale junctionless tunneling FET: concept and scaling capability

In this paper, a new nanoscale double-gate junctionless tunneling field-effect transistor (DG-JL TFET) based on a Si1−xGex/Si/Ge heterojunction (HJ) structure is proposed to achieve an improved electrical performance. The effect of introducing the Si1−xGex material at the source side on improving the subthreshold behavior of the DG-JL TFET and on suppressing ambipolar conduction is investigated. Moreover, the impact of the Ge mole fraction in the proposed Si1−xGex source region on the electrical figures of merit (FoMs) of the transistor, including the swing factor and the ION/IOFF ratio is analyzed. It is found that the optimized design with 60 atom % of Ge offers improved switching behavior and enhanced derived current capability at the nanoscale level, with a swing factor of 42 mV/dec and an ION/IOFF ratio of 115 dB. Further, the scaling capability of the proposed Si1−xGex/Si/Ge DG-HJ-JL TFET structure is investigated and compared to that of a conventional Ge-DG-JL TFET design, where the optimized design exhibits an improved switching behavior at the nanoscale level. These results make the optimized device suitable for designing digital circuit for high-performance nanoelectronic applications

Highly improved responsivity of self-powered UV–Visible photodetector based on TiO2/Ag/TiO2 multilayer deposited by GLAD technique: Effects of oriented columns and nano-sculptured surface

International audienceThe outstanding progress made in optoelectronic technologies calls for a renewed performance assessment of photodetectors (PDs) for next-generation sensing applications. Here, TiO2/Ag/TiO2 tri-layered films were sputtered using the GLancing Angle Deposition (GLAD) technique in which the deposition angle was varied from 0 to 80°. Before the elaboration, a strategic combination of Genetic Algorithm (GA) and numerical analysis was used to find out the best multilayer geometry offering superior optical performance. The influence of the inclinedarchitecture on the performance of the prepared TiO2/Ag/TiO2 multilayer was analyzed. Optical characterization reveals that near-perfect UV photodetection and over than 60% of visible-absorbance were achieved by taking a deposition angle of 80°. These enhancements are correlated to the surface nano-sculptured structures, which gives rise to an enhanced light-trapping capability. The measured I-V curves of the obliquely-deposited structures showed a clear photovoltaic mode and an extremely low dark current of a few picoamperes. Besides, the devices demonstrate an enhanced self-powered UV–Vis photoresponse, yielding superb UV and visible responsivity of 0.2A/W and 47 mA/W, respectively. The UV, blue, and green current ratios were respectively 137, 113, and 107 dB. Therefore, promoting efficient light management, this innovative concept of inclined tri-layer films provides a sound pathway for designing potential alternative self-powered UV–Vis PDs appropriate for the future development of the optoelectronic technology

Tunable band-selective photodetector based on sputter-deposited SnOx thin-films: Effect of reactive gas pulsing process

International audienceIn this work, high-performance SnOx band-selective photodetectors(PDs) were realized by DC magnetron sputtering technique. Thereactive gas pulsing process (RGPP) was implemented with pulsingperiod fixed at P = 20 s to adjust tin and oxygen concentrations inthe film. The impact of pulsed oxygen time on the structural,morphological and photosensing properties of SnOx-based PDs wasinvestigated. The fabricated SnOx-based PD at a high duty cycle of80% of P demonstrated high UV photodetection capabilities andsolar-blind characteristic with a high responsivity of 21.8 mA/W, ahigh signal to noise ratio of 6×104 and a specific detectivity ofabout 5×1011 Jones. It was also revealed that the use of a shortoxygen pulsing time 8 s paves the way for the realization ofmultispectral SnOx PD, demonstrating a high responsivity values of36.45 mA/W, 36.4 mA/W and 34 mA/W over UV, Visible and NIR bands,respectively. This is attributed to the role of using RGPP inmodulating the film optoelectronic properties from metallic toinsulator when the duty cycle and thus oxygen concentration in thefilms changed from pure tin to overstoichiometric SnO2 compound.The prepared SnOx PDs demonstrated many advantageous features likelow-noise, cost effective and high sensitivity. The obtainedresults proved that SnOx can be used as an alternative material fordeveloping high-performance band-selective sensing devices

Highly sensitive, ultra-low dark current, self-powered solar-blind ultraviolet photodetector based on ZnO thin-film with an engineered rear metallic layer

International audienceIn this paper, novel self-powered, solar-blind UV photodetector (PD) designs based on a ZnO thin-film with engineered back metal layer (BML) were fabricated by RF magnetron sputtering and e-beam evaporation techniques. An exhaustive study concerning the impact of dissimilar BML (Au and Ni) on the device structural, optical and electrical properties was carried out. The measured I–V curves illustrated an asymmetrical behavior, enabling a clear and distinctive photovoltaic mode. Superb sensitivity of 107, high ION/IOFF ratio of 149dB, ultralow dark-noise current less than 11pA and responsivity exceeding 0.27A/W were reached for the prepared ZnO-based UV-PDs in self-powered mode. The role of the engineered BML in promoting effective separation and transfer of the photo-induced carriers was discussed using the band-diagram theory. The influence of the annealing process on the UV-sensor performance was also investigated. The annealed device at 500°C demonstrated a lower dark current of a few picoamperes and a high rejection ratio of 2.2:103, emphasizing its exciting visible blindness characteristics. Therefore, the use of an engineered BML with optimized annealing conditions open up new perspectives to realizing high-performance, self-powered solar-blind UV-PDs based on simple thin film-ZnO structure strongly desirable for various optoelectronic applications

Microstructured ZnO-ZnS composite for earth-abundant photovoltaics: Elaboration, surface analysis and enhanced optical performances

International audienceIn this paper, ZnO-ZnS composite structure is proposed as a new efficient and earth-abundant absorber material for thin-film solar cells (TFSCs). Promising elaboration strategy based on combining vacuum thermal evaporation technique and oxidation process under an annealing temperature of 500°C was used to prepare ZnO-ZnS composite with high sun-light absorption capabilities. The fabricated microstructure was then characterized by Scanning Electron Microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and UV–Visible absorption spectroscopy. The influence of the annealing time on the structural and optical performances of the prepared samples was investigated. Surface analysis demonstrated the ZnO decoration of ZnS thin-film, where SEM images showed dense and pinhole-free ZnO-ZnS composite with micrometer-sized grains and a few voids visible at thin-films surface. Optical characterization showed that the prepared thin-film absorber exhibits an optical band-gap of 2.65 eV with a high Total Absorption Efficiency (TAE) of 62% and an absorption coefficient exceeding 2 × 104 cm−1. In addition, I-V characteristics under dark and 1-sun illumination of the microstructured ZnO-ZnS composite were extracted. It was revealed that the proposed absorber showcases a high visible photoresponse. Therefore, promoting effective light-scattering effects, this innovative ZnO-ZnS composite offers a sound pathway to prepare alternative low-cost absorbers for the future development of TFSCs