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

An original way to obtain porous Zn(1–x)MgxO thin films by spray pyrolysis technique

Zn(1–x)MgxO thin films with various concentrations of magnesium were deposited using the spray pyrolysis method. The transmittance spectra recorded for all films exhibit maxima exceeding 90%. The band gap energy of the films with wurtzite structure increases from 3.22 up to 3.60 eV by incorporating Mg into ZnO. However, when the atomic ratio of Mg exceeded 0.4, a second crystalline phase (assigned to cubic MgO) became discernable in XRD patterns, a compressive strain was observed in the wurtzite lattice, and crystallite sizes decreased significantly. In accordance with these observations, finer grains with a pronounced columnar growth were observed in 3D AFM representations and the surface roughness decreases significantly. Finally, selective etching in water yields to porous films with a great surface-to-volume ratio, a lower refractive index and a better light transmission. These porous films with tunable band gap seem to be excellent candidates to various interesting 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