Francisco Javier Flores-Ruiz

Zinc oxide is one of the prominent materials for optoelectronic applications. Chemical and physical growth methods strongly influence its properties, which can be tailored by incorporating suitable dopants. This work explores the electrical properties of Ga doped ZnO films grown by rf sputtering under photon excitation from a tungsten-halogen lamp. Experiments were performed under short and long transient illumination conditions. The characteristic times during light on/off cycles were determined. The fastest response was observed for undoped films, indicating that Ga introduces deep traps in the band gap, slowing photoresponse dynamics. Structural, optical and dark electrical properties were also analyzed as a function of Ga concentration and substrate temperature. Ga doping improved conductivity in all samples. Films grown at 300 ºC with 3 at.% showed the best conductivity. A correlation between the slope of infrared transmittance and free electron density was observed. Terahertz spectroscopy probed deep levels in the ZnO band gap, revealing an inverse correlation between conductivity and IR absorbance (0.11–0.99 eV). The work function was 4.46 eV for undoped ZnO and 4.61 eV for films with 5 at.% Ga.

Zinc oxide is one of the prominent materials for optoelectronic applications. Chemical and physical growth methods strongly influence its properties, which can be tailored by incorporating suitable dopants. This work explores the electrical properties of Ga doped ZnO films grown by rf sputtering under photon excitation from a tungsten-halogen lamp. Experiments were performed under short and long transient illumination conditions. The characteristic times during light on/off cycles were determined. The fastest response was observed for undoped films, indicating that Ga introduces deep traps in the band gap, slowing photoresponse dynamics. Structural, optical and dark electrical properties were also analyzed as a function of Ga concentration and substrate temperature. Ga doping improved conductivity in all samples. Films grown at 300 ºC with 3 at.% showed the best conductivity. A correlation between the slope of infrared transmittance and free electron density was observed. Terahertz spectroscopy probed deep levels in the ZnO band gap, revealing an inverse correlation between conductivity and IR absorbance (0.11–0.99 eV). The work function was 4.46 eV for undoped ZnO and 4.61 eV for films with 5 at.% Ga.

Dual physical–chemical modification of cellulose nanocrystals enables high-performance gelatin eutectogels. Dynamic CNC–COOH/TA assemblies impart strain-sensing capability and contact-mediated antibacterial functionality for greener iontronics.

Multilayer heterostructures of [(BiFeO₃)_m/(SrTiO₃)_n]_p were synthesized on ITO-coated quartz substrates via pulsed laser deposition, with varying thickness ratios (r = n/m) and periodicities (p = 1–3). Structural, electrical, and piezoelectric properties were systematically investigated using X-ray diffraction, AFM, and PFM. The BiFeO₃ layers crystallized in a distorted rhombohedral phase (R3c), free of secondary phases. Compared to single-layer BiFeO₃ films, the multilayers exhibited markedly lower leakage current densities and enhanced piezoelectric response. Electrical conduction transitioned from space-charge-limited current at low fields (E < 100 kV/cm) to Fowler–Nordheim tunneling at high fields (E > 100 kV/cm). Optimal performance was achieved for r = 0.30, p = 1, with minimal leakage (J = 8.64 A/cm² at E = 400 kV/cm) and a peak piezoelectric coefficient (d₃₃ = 55.55 pm/V). The lowest coercive field (Ec = 238 kV/cm) occurred in the configuration r = 0.45, p = 3. Saturated hysteresis loops confirmed stable ferroelectric domains. These findings demonstrate that manipulating layer geometry in [(BiFeO₃)_m/(SrTiO₃)_n]_p stacks significantly enhances functional properties, offering a viable path toward efficient, lead-free piezoelectric nanodevices.

Adjacent compensated codoping (alloying) is presented as an alternative approach to modify the electrical and optoelectronic properties of semiconductors.

The overall performance of the multilayer resulting in a sol-gel bismuth ferrite (BiFeO₃) film will be primarily determined by the properties of the first layer, but this has yet to receive much attention, even though chemical and morphological defects of this layer can accumulate as the number of layers increases. Here, we perform an optical, conductive, and ferroelectric study of first layer (L ₁) dip-coating sol-gel BiFeO₃ films using two routes that vary only in the dissolvent; the first one is based on 2-methoxyethanol (MOE), and the second one on acetic acid (AA) with some MOE (AA-MOE). Tauc plots reveal a band gap of 2.43 eV and 2.75 eV for MOE (30 ± 5 nm thick) and AA-MOE (35 ± 5 nm thick) films, respectively. MOE films showed a dielectric function with features at ∼2.5 eV, ∼3.1 eV, and ∼3.9 eV, which were associated with charge-transfer transitions, but such features are absent in AA-MOE films. Advanced atomic force microscopy techniques were used to identify the fine features or defects of the BiFeO₃ films: The conductive maps show that the charge transport pathways in both film routes are controlled by nanometer defects rather than grain or grain boundary defects. Current-voltage curves reveal high conductive pathway at a lower voltage for the MOE films than for AA-MOE films. The piezoelectric coefficient for MOE films was ∼20% higher than AA-MOE films. Both deposition methods yield ferroelectric films with an electromechanical strain controlled by the piezoelectric effect and minimal contribution from electrostriction. An optimization for the AA-MOE-based route in the withdrawal speed results in a significant reduction of morphological defects and a more than twofold increase in the piezoelectric coefficient. Our results broaden the understanding of optical and ferroelectric BiFeO₃ films based on a chemical solution by dip-coating.

Numerical calculations were performed on NbN/Nb and TiN/Ti nanostructured bilayers. Discrete dipole approximationimplemented in the DDSCAT code was utilized. In order to design a TUC (Target Unit Cell) with realistic surfaceroughnesspattern, Atomic Force Microscope images of 100 ±10 nm Nb thin films were used. The optical properties of nanostructured bilayers (60-100 nm thickness with a ±10 nm surface roughness) were calculated, keeping the interfacebetween the layers as smooth flat surfaces. For the NbN/Nb nanostructure with a thickness between 100 ±10 nm, and 70 ±10 nm, in a wavelength range between 200 and 350 nm, the reflectance and absorptance show a nearly flat spectrumwith an intensity of 20% and 80%, respectively. For larger wavelengths, absorptance decays smoothly. In contrast, for the 60 ±10 nm bilayer, the absorptance decays faster. For the TiN/Ti nanostructure, at 415 nm, a relative maximum in the reflectance, and a minimum in absorptance, are observed. The critical value of the absorbed light spectra begins to shift to higher wavelengths as the thickness of the TiN layer increases. We demonstrate that adding a rough nitride layer on top of its metallized layer drastically modifies the optical response of the nanostructured bilayer, an interesting result forplasmonics and nanoelectronics applications.