Miguel Meléndez Lira

Silicon-compatible near-infrared photosensitive heterostructures are attractive for integrated optoelectronics, but in group-IV nanocrystal (NC) structures on crystalline silicon, a spectral maximum near the Si absorption edge cannot be assigned to the nanocrystals from wavelength alone. Here, oxygen partial pressure (OPP) during reactive radio frequency sputtering is treated as a process variable that modulates the steady-state photoresponse of coupled SiO2/Ge-nanocrystal/SiO2/p-Si heterostructures. Stacks containing a nominal 4.7 nm Ge interlayer were grown at 400 °C using 25%–75% OPP. The revised analysis combines OPP-dependent spectral photoresponse, dark/illuminated current-voltage characteristics, a process-matched Ge-free oxide control at OPP75, wavelength-dependent incident-power calibration, and a layer-resolved transfer-matrix/effective-medium model constrained by previously published morphology. Across the Ge-containing series, the response maximum spans approximately 1014–1130 nm with an overall redshift and narrowing, although the intermediate-OPP values are nonmonotonic. The matched oxide-only control shows a broader substrate-edge-like response and does not reproduce the narrow high-amplitude band of OPP75EG47 near 1130 nm, demonstrating an additional contribution associated with the Ge-containing interlayer/interfaces without implying that Ge-NCs are the dominant absorber. A representative device remains strongly nonideal (ideality factor about 2.1; series resistance about 75 kΩ). Conservative optical bounds show that the Ge-NC:SiO2 region absorbs less than approximately 2% of incident power at the measured maxima, whereas the Si substrate absorbs roughly 7%–81%. The NIR response is, therefore, best described as substrate-assisted and overlayer-modulated. The contribution of this work is a process-structure-photoresponse attribution framework rather than a performance-optimized photodetector.

(CdTe)1-xAlx films, with 0.01 < x < 0.08, were deposited on soda lime glass and p-type Si(111) substrates by RF co-sputtering using CdTe and aluminum targets. The aluminum content (x) in the films was controlled by the sputtering power applied to the aluminum target, reaching up to x = 0.08 using 100 W. On the other hand, the maximum bandgap value of 1.59 eV was obtained for x = 0.07 deposited employing 80 W. X-ray diffraction patterns suggest that the solubility limit of aluminum in the CdTe lattice is close to x = 0.08. X-ray photoelectron spectroscopy (XPS) analysis suggests a pseudo-alloy-like behavior in the (CdTe)1-xAlx system, as evidenced by the presence of a Te–Al contribution. Optical constants of the (CdTe)1-xAlx films were obtained from the analysis of transmission spectra and were found to be systematically lower than those of bulk CdTe. Electrical measurements for (CdTe)1-xAlx films deposited on p-type Si(111) substrates exhibited rectifying current–voltage (I-V) behavior. Furthermore, the measured photoresponse suggests that (CdTe)1-xAlx films exhibit an optoelectronic activity worth to pursue their study to evaluate practical applications.

Este estudio presenta el modelado de nanocristales de silicio en una matriz de SiO2 para aplicaciones optoelectrónicas, destacando el confinamiento cuántico. Utilizando la teoría en la aproximación isotrópica, se analizan las propiedades electrónicas de estos nanocristales. La función envolvente de los electrones y huecos se describe mediante la ecuación de Schrödinger en la aproximación de masa efectiva, considerando una barrera de potencial abrupta y esférica. Los estados propios se obtienen numéricamente, proporcionando una descripción detallada de la estructura electrónica. El cálculo de los niveles de energía se realiza encontrando los ceros de una ecuación no trivial, y se determinan parámetros analíticos que limitan el tiempo de cálculo en función del radio del nanocristal. Este enfoque teórico permite obtener el gap electrónico en función del radio del nanocristal, validado con muestras experimentales. El objetivo es mostrar la utilidad de la mecánica cuántica en la predicción del comportamiento de los materiales, incentivando a ingenieros en materiales y nanotecnólogos a comprender su relevancia.

Si nanoparticles embedded in a ZnO matrix were produced by a sequential deposition of ZnO/Si/ZnO layers, by radio frequency sputtering. Sample growth temperatures of 25 °C, 300 °C, and 500 °C were used to deposit ZnO/Si/ZnO layers on soda lime glass and p-type silicon substrates; ZnO layers were deposited by reactive radio-frequency sputtering employing a mixture of Ar/O_2, with a ratio of 66/33, as working atmosphere. The type of substrate and the growth temperature affect the first ZnO layer roughness, promoting the formation of silicon nanoparticles, matrix characteristics, and as consequence, spectral response. The roughness of the initial ZnO layer is transferred to the top layer of ZnO, and it can be tailored between 65 and 370 Å, depending on the sample growth temperature. Transmission electron microscopy show that substrate temperature mainly affects the density of silicon nanoparticles rather than their size. ZnO/Si/ZnO films deposited on p-type silicon substrate were processed and photosensors were obtained, showing a selective response in the 950 to 1150 nm wavelength range, making them suitable candidates for near infrared detectors.

(CdTe)_1-x(In₂Te₃)_x films, with 0.1 ≤ x ≤ 1, were deposited by radio frequency sputtering on glass substrates employing different targets, prepared for each composition. The x-ray diffractograms were consistent with substitutional In incorporation into the CdTe lattice up to a value of x = 0.2. For higher In contents, the films presented structural disorder without reaching full amorphous characteristics. For x = 1, corresponding to In₂Te₃, preferential growth was observed. The bandgap of the solid solution varied between 1.46 and 1.2 eV, reaching a maximum of 1.58 eV for x = 0.3. For both end binary compounds the random incorporation of a third chemical element produced a significant broadening of the Raman modes consistent with a reduction of the lifetime of the optical phonons. The electrical resistivity was dependent on the Cd concentration reaching a minimum for x = 0.8.

Fe2O3-ZnO composite gained attention due the several applications like that sensors, photocatalysis, reduction of mercury ions. Fe2O3-ZnO composite thick films were prepared by Ultrasonic Spray Pyrolysis on a glass substrate, using 0.1 M aqueous solutions of FeCl3?6H2O and ZnCl2 anhydride. To obtain different elemental concentration of Fe and Zn, we varied the volume of each aqueous solution. The XPS analysis shown that it is possible to modulate the concentration of Zn and Fe in the samples. The X-ray diffraction measurements revealed that the films were composed of different phases corresponding with common stable iron oxides (ZnFe2O4, Fe2O3) and zinc oxide (ZnO). Results from Raman spectroscopy indicate that Fe2O3 vibrational modes are accompanied with new modes due to the presence of additional phases ZnO compounds. The band gaps were evaluated with the help of UV-visible transmittance data using the Tauc model, the results shown a modulation of the band gap values (2.2 eV to 3.2 eV). Theorical transmittance curves were obtained using the effective medium theory, using the Bruggeman model, these curves showed similar behavior that the experimental transmittance curves.

In order to control the deposition of Zn-related films by chemical bath deposition, the effects of Zn-complexing agent are analyzed. ZnS films were produced by chemical bath deposition technique employing sodium citrate, ethanolamine and Triethanolamine as complexing agents. The deposition conditions for ZnS (ZnO) thin films were obtained through a thermodynamic analysis, using distribution diagrams for molar fraction of Zn complexes. From species distribution diagrams of Zn-ethanolamine, Zn-Triethanolamine and Zn-citrate. It was found that for pH values between 4 and 6 the highest Zn fraction is obtained. The results highlight the importance of complexing agent morphology, while the use of ethanolamine and triethanolamine produce ZnO films due to their high reactivity; the use of sodium citrate produce ZnS films. Deposited ZnS films have a cubic structure, n-type conductivity, resistivity of 8.36×104 ??cm with a 3.75 eV bandgap.