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Microstructured films of undoped zinc oxide (ZnO) and ZnO doped with nickel (ZnO:Ni) were grown by hot filament chemical vapor deposition (HFCVD) technique on Si (100) substrates at 500 °C. Pellets of ZnO and ZnO:NiO as oxidant agenst were used. A shift to the right around 0.17 degree of the X-Ray Diffraction pattern of the ZnO:Ni film was observed with respect to undoped ZnO films. Morphologically by Scanning Electron Microscopy was noticed a Core-Shell type growth in ZnO undoped and a nanostructured type (Nano-wire) in ZnO doped with Ni. Photoluminescence measurements showed an increase in the intensity of the green emission band of ZnO:Ni. It was attributed to defects of oxygen vacancies (VO), zinc vacancies (VZn), zinc interstitials (Zni), oxygen interstitials (Oi), and oxygen vacancies complex (VO complex) in the structure of the film. The incorporation of Ni atoms in the ZnO structure stresses the crystal lattice, leaving behind a large number of surface defects that increase the emission of PL.

Tin sulfide (SnS) thin films were successfully deposited on acetate plastics substrates by chemical bath deposition at 70 °C by 2 h varying the pH value. SnS films exhibited good adherence, compact and uniform. X-ray diffraction (XRD) results showed that it is possible to obtain cubic, amorphous, and orthorhombic crystalline structures for SnS films depending on the pH value in a range from 8.24 to 10.93. Scanning electron microscopy (SEM) analysis revealed a morphological transformation of SnS films from spherical shape to flakes shape for cubic and orthorhombic structures, respectively. The pH variation influences on SnS films stoichiometry, for low pH the S/Sn ratio is 0.15 while for pH around of 10.45 the S/Sn ratio is 0.90 which is near-stoichiometric. Raman studies confirm SnS vibrational modes associated with cubic and orthorhombic structure. Optical properties also were modified varying the pH and the absorption coefficients are larger than 104 cm−1 for all SnS films deposited on acetate plastic substrates. The band gap values were obtained from 1.08 to 1.72 eV and associated with cubic, amorphous, and orthorhombic SnS. The results suggest that it is possible to modify the crystalline structure, band gap, and S/Sn ratio varying the pH value, and this work promotes the application of SnS in flexible devices.

The effect of the deposit temperature of zinc oxide (ZnO) doped with nickel (Ni) by hot filament chemical vapor deposition (HFCVD) technique is reported in this work. The technique allows depositing ZnO:Ni in short intervals (1 min). A deposit of undoped ZnO is used as a reference sample. The reference sample was deposited at 500 °C. The ZnO:Ni samples were deposited at 500 °C, 400 °C, 350 °C, and 300 °C. The samples were studied using structural, morphological, and optical characterization techniques. The Ni incorporation to the ZnO lattice was verified by the shift of the X-ray diffraction peaks, the Raman peaks, the band gap, and the photoluminescence measurements. It was found that the deposit temperature affects the structural, morphological, and optical properties of the ZnO:Ni samples too. The structure of the ZnO:Ni samples corresponds to the hexagonal structure. Different microstructures shapes such as spheres, sea urchins, and agglomerate were found in samples; their change is attributed to the deposit temperature variation. The intensity of the photoluminescence of the ZnO:Ni improves concerning the ZnO due to the Ni incorporation, but it decreases as the deposit temperature decreases.

In this work, SnS films were deposited on copper substrates under different pH values by chemical bath deposition. The pH values were varied from 8.44 to 11.26 and SnS films were obtained at 10.62. Films of Sn6O4(OH)4 were obtained for pH values lower than 10.62 and mixed phases of SnS and Sn2S3 were formed at pH 11.26. The deposition parameters were 70 °C for 3 h for all samples. Structural, morphological and optical properties were analyzed by XRD, SEM and UV–Vis–NIR respectively. In addition, vibrational modes for Sn6O4(OH)4 and SnS films were identified by Raman spectroscopy from 60 to 380 cm−1. SnS films exhibited an orthorhombic structure and a crystal size of 15 nm. The morphology of the films was transformed from pyramidal to rice shape as the pH was increased. Gap value for Sn6O4(OH)4 films was found to be 3.11 eV and for SnS was 1.17 eV, however, for mixed SnS and Sn2S3 films the gap value was 0.61 eV. The thickness of SnS films was around 1.7 micrometers, which is an appropriate value for solar cells applications as absorber material.

Zn-doped GaN powders were obtained by supersaturation of the Ga-Zn liquid metallic solution at 440 °C, followed by a nitridation process in ammonia flow at 1000 °C for two hours. Photoluminescence spectrum measured at room temperature for Zn-doped GaN powders, showed an emission band with a maximum energy of 2.89 eV (429 nm), which might be related to the excitons binding to the Zn acceptors. The Raman spectra agree with the incorporation of Zn as dopant into GaN powders, demonstrating a shoulder at 651.89 cm−1 and a slight shift (1.55 cm−1) to low frequency of the vibration mode A1(TO) with respect to undoped GaN powders. The Raman spectra showed a separation between the E1(TO) and E2(High) modes, confirming that Ga-rich GaN was obtained. X-ray diffraction patterns did not show any shift of the peaks of the Zn-doped GaN with respect to the undoped GaN powders. Scanning electron microscopy micrographs demonstrated that the surface morphology of the Zn-doped GaN powders was composed of platelets of irregular structure with an average length of 2.80 μm. Finally, x-ray photo-electron spectroscopy spectra did not show an important elemental contribution of zinc due to the small amount of the dopant element (1.05 mol%).

Hexagonal nanocrystals into Al0.2Ga0.8N and Al0.6Ga0.4N powders via pyrolysis from an organometallic compound, followed by a nitridation process in ammonia flow at 1000 °C for two hours were obtained. X-ray diffraction patterns demonstrated a shift towards greater angles to the right for the AlGaN powders with respect to GaN powders, this shift could indicate the formation of the AlGaN powders. Scanning electron microscopy micrographs showed the obtaining from semi-plates of porous appearance for the Al0.2Ga0.8N powders until well-defined plates for the Al0.6Ga0.4N powders. High resolution transmission electron microscopy micrographs demonstrated the presence of hexagonal nanocrystals into Al0.2Ga0.8N powders with an average crystal size of 10.3 nm, while that for the Al0.6Ga0.4N powders an average crystal size of 9.7 nm was observed. UV-visible spectra showed a transmittance cut-off for the Al0.2Ga0.8N powders of 3.71 eV (334.2 nm) and a transmittance cut-off of 4.53 eV (273.7 nm) for the Al0.6Ga0.4N powders.

Undoped GaN layers were grown via radio-frequency magnetron sputtering, using a target manufactured with undoped GaN powders. Where the GaN powders were sintetized by nitridation of metallic gallium at 1000 °C in ammonia flow for two hours. X-ray diffraction patterns demonstrated that there are not a significant difference between the diffraction angles of the GaN powders and the GaN layers. The x-ray diffraction patterns for the GaN powders showed narrow peaks with a crystal size of 41 nm, while the GaN layers showed broad peaks with a crystal size of 7.7 nm. Scanning electron microscopy micrographs demonstrated the formation of crystals of irregular size with an average length of 1.56 ?m for the GaN powders, while a homogeneous surface morphology with a thickness of 6.6 ?m for the GaN layers was observed. Photoluminescence spectra showed a high emission at 3.49 eV (355.13 nm) for the GaN powders and an emission band energy located at 3.42 eV (361.54 nm) for the GaN layers, both emission bands were related to the band-to-band transition for the GaN. Raman spectra for the GaN powders showed the A1(TO), E1(TO), and E2(High) classical vibration modes. The GaN layers only showed the A1(TO) mode.

AlxGa1-xN powders were obtained by pyrolysis route of the (CH6N4O)3 Al-Ga(NO3)3 organometallic complex, followed by an annealing in anhydrous ammonia flow at 1000 °C during two hours. Pyrolysis temperatures were experimentally determined in a range from 200 to 285 °C, which was systematically checked by thermal gravimetric analysis and differential scanning calorimetry, and whose results agree with the experimental pyrolysis temperatures. X-ray diffraction patterns for the AlxGa1-xN powders showed a slight shift towards greater angles, when the aluminum concentration increases. Scanning electron microscopy micrographs, showed the presence of agglomerates, which generate the formation of not well-defined plates with rough texture into the AlxGa1-xN powders. However, high-resolution transmission electron microscopy micrographs showed well-defined nanocrystals with a crystal size of 9 nm. Energy dispersive spectroscopy showed that there is no presence of carbon atoms in the AlxGa1-xN powders. Cathodoluminescence spectra for the AlxGa1-xN powders showed emissions in a range from 359 nm (3.45 eV) to 205 nm (6.04eV) (UV region).

Orthorhombic tin sulfide (SnS) thin films have been deposited on stainless steel (SS) substrates by Chemical Bath Deposition (CBD) at 25, 35 and 70 °C with a deposit time of 8 hours each one. XRD analysis showed that samples obtained at 25 °C and 70 °C present very small diffraction peaks. This can be attributed in the case of the sample obtained at 25 degrees, that the crystallization process is not completed because the temperature is so low and in case of the sample deposited at 75 degrees, a redissolution of the material is carried out. However, sample obtained at 35 °C was polycrystalline with orthorhombic structure and preference plane (111). All samples showed the Raman vibrational modes TO and LO of the SnS and confirms that the samples do not have by-products. It was observed from SEM micrographs that the films consisted of spheres for the sample deposited at 25 °Candsmall flakes for the other samples. From diffuse reflectance measurements the optical band gap calculated was between 1.45 eV to 1.59 eV.

Orthorhombic tin sulfide (SnS) thin films have been deposited on stainless steel (SS) substrates by Chemical Bath Deposition (CBD) at 25, 35 and 70 °C with a deposit time of 8 hours each one. XRD analysis showed that samples obtained at 25 °C and 70 °C present very small diffraction peaks. This can be attributed in the case of the sample obtained at 25 degrees, that the crystallization process is not completed because the temperature is so low and in case of the sample deposited at 75 degrees, a redissolution of the material is carried out. However, sample obtained at 35 °C was polycrystalline with orthorhombic structure and preference plane (111). All samples showed the Raman vibrational modes TO and LO of the SnS and confirms that the samples do not have by-products. It was observed from SEM micrographs that the films consisted of spheres for the sample deposited at 25 °Candsmall flakes for the other samples. From diffuse reflectance measurements the optical band gap calculated was between 1.45 eV to 1.59 eV.

Magnesium doped GaN powders were obtained by nitridation of a Ga-Mg liquid metallic solution in a chemical vapor deposition system during two hours at 1000 °C. Photoluminescence spectrum, obtained at room temperature of the Mg doped GaN powders, showed an emission band with a maximum energy of 2.9 eV (427.5 nm), which is characteristic of Mg doped GaN. Raman spectra agree with the incorporation of Mg as dopant in the GaN powders, showing a shoulder at 669.98 cm−1 and a slight shift to low frequency of the vibration mode A1(TO) with respect to undoped GaN powders. X-ray diffraction patterns suggested that the crystalline structure of the GaN powders was not affected by the incorporation of Mg into the lattice. Finally, scanning electronic microscope images showed that the surface morphology of the Mg doped GaN powders was composed of hexagonal platelets, which could be due to the magnesium diffusion in the gallium before the nitridation process takes place.

Optical and structural study of undoped GaN powders obtained by nitridation of metallic gallium and pyrolysis of Ga(NO3)3-CH6N4O polymer were made. A high synthesis efficiency for the nitridation of metallic gallium was observed, while the pyrolysis synthesis of the Ga(NO3)3-CH6N4O polymer was very low. The XRD patterns showed an intense peak in the orientation (101) of the hexagonal GaN in both cases. The photoluminescence spectrum for nitridation technique of metallic gallium at room temperature, shown how the point defects generated during the preparation of GaN powders allow the adequate incorporation of nitrogen and favor the crystal growth (sizes up to 3.6 μm length and 3 μm wide). The visible separation in the micro-Raman spectrum of the E1 and E2 modes in the samples obtained by nitridation of metallic gallium was an indicative of the contribution of interstitial gallium in the lattice vibration, an aspect not reported yet. On the other hand, SEM studies confirmed the higher crystalline size of the material obtained by nitridation of metallic gallium compared with the synthesized by pyrolysis of the Ga(NO3)3-CH6N4O metalorganic complex polymer.

ZnSe nanoparticles (ZnSe-NPs) were obtained by aqueous colloidal solution at room temperature (25 °C) at different pH. A physicochemical study of the aqueous solution was proposed. The chemical reagents of the colloidal solution were zinc chloride, selenium elementary powder, Extran® as a surfactant, and sodium borohydride as a reducing agent. The species distribution diagrams (SDDs) and solubility curves (SCs) as pH functions were plotted as a result of the physicochemical analysis. The SDDs and SCs predicted the ZnSe-NPs formation and their growing process, therefore, a series of experiments according to these diagrams were performed at various pH of the colloidal solution through different Extran® content. The ZnSe-NPs were obtained without further purification. The ZnSe-NPs were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) techniques. The XRD results revealed that the ZnSe-NPs have mixed cubic and hexagonal crystalline structures, with crystal size at the nanoscale. The Raman spectra exhibited two peaks at 253 cm−1 of the longitudinal optical (LO) phonon mode, and 235 cm−1 of the surface phonon mode corresponding to the ZnSe bulk. The SEM images showed a variety of morphologies with different Zn/Se atomic ratios estimated from the EDS analysis.

Tantalum oxide crystals encrusted in a silicon oxide matrix were synthesized by using a hot filament chemical vapor deposition system (HFCVD). A solid source composed by a mixture in different percentages of Ta2O5 and silicon (Si) powders were used as reactants. The films were grown at 800 °C and 1000 °C under hydrogen ambient. The deposited films were characterized by X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM) and photoluminescence (PL) at room temperature. From the XPS results it was confirmed the formation of a mixture of Tantalum oxide, silicon oxide and Si nanoparticles (Ta2O5-SiO2-Si(nc)) as seen from the Si (2p) and Ta (4f) lines corresponding to Si+ and Ta+ states respectively. Ta2O5 and Si nanocrystals (Si-NCs) embedded in the silicon oxide films were observed on HRTEM images which corroborate the XPS results. Finally the emission properties of the films exhibited a broad band from 400 to 850 nm caused by the independent PL properties of tantalum oxide and Si-NCs that compose the film. The intensity of the emissions was observed to be dependent on both temperature of deposition and the ratio Ta2O5/Si, used as initial reactants. Results from this work might supply useful data for the development of future light emitter devices.

Silicon oxycarbide thin films were obtained by catalytic chemical vapor deposition technique using mesoporous silica pellets and tetraethoxysilane as reagents. Energy-dispersive X-ray spectroscopy demonstrated the presence of silicon, oxygen, and carbon, which agreed with X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy characterization results. Scanning electron microscopy images showed the presence of globular clusters with an average size of 221.8 nm containing dispersed aggregates as much as 50 nm in diameter dispersed on their surface. Ellipsometry measurements showed that the thickness of thin films increased at higher hydrogen flow rates during the deposition process. Photoluminescence spectra showed a luminescence enhancement for the samples prepared with mesoporous silica pellets and tetraethoxysilane as reagents.

We present zinc oxide (ZnO) particles obtained inside a porous silicon matrix in the same electrolytic process using a p-type silicon wafer in a hydrofluoric acid (HF) solution containing formaldehyde (CH2O) and hydrated zinc sulfate as additives. The X-ray diffraction pattern of the sample confirmed the presence of ZnO with a hexagonal-type wurtzite structure. Photoluminescence (PL) spectra of the samples, before and after the functionalization process, were measured to observe the effect of ZnO inside the porous silicon. The PL measurements of porous silicon functionalized with ZnO (ZnO/PS) revealed infrared, red, blue, and ultraviolet emission bands. The ultraviolet region corresponds to the band-band emission of ZnO, and the visible emission is attributed to defects. The results of the nitrogen adsorption/desorption isotherms of the PS and ZnO/PS samples revealed larger BET surface areas and pore diameters for the ZnO/PS sample. We conclude that ZnO/PS can be obtained in a one-step electrolytic process. These types of samples can be used in gas sensors and photocatalysis.

The effect of the gaseous atmosphere in the growth of gallium arsenide (GaAs) films was studied. The films have been grown by close-spaced vapor transport (CSVT) technique in a home-made hot filament chemical vapor deposition (HFCVD) reactor using molecular hydrogen and molecular nitrogen as the transport agent. An important point about the gaseous atmosphere is the ease in creating volatile compounds when it makes contact with the GaAs source, this favors the transport of material in a CSVT system. Chemical reactions are proposed in order to understand the significant difference produced from the gaseous atmosphere. The films grown with hydrogen are (almost) continuous and have homogeneous layers with preferential orientation (111). The films grown with nitrogen are granular and rough layers with the coexistence of the orientations (111), (220) and (311) in the crystals. The incorporation of impurities in the films was corroborated by energy dispersive spectroscopy (EDS) showing traces of oxygen and nitrogen for the case of the samples obtained with nitrogen. Films grown in a hydrogen atmosphere show a higher band gap than those grown in a nitrogen atmosphere. With the results of XRD and micro-Raman we observe a displacement and broadening of the peaks, characteristic of a structural disorder. The calculations of the FWHM allow us to observe the crystallinity degree and determine an approximate crystallite size using the Scherrer&rsquo, s equation.

The theoretical and experimental study of porous silicon-based UV microcavities is discussed in this work. The obtaining of CMs in the Ultraviolet range expands the field of research of porous silicon photonic structures. The porous silicon microcavities (PSM) consisted of two Bragg reflectors (BRs) with a defect between them. It was fabricated by electrochemical etching. Microcavities (MCs) were subjected to dry oxidation process (DOP). In this way we obtained an oxidized porous silicon (OPS) that induces a shift of the response to the ultraviolet (UV) region on both, the minimum peak of the reflectance spectrum and the maximum peak of the transmittance spectrum; two UV microcavities showed maximum transparency in the UV of 67 %. The shift is explained as due to the formation of silicon dioxide (SiO₂); this wavelength shift shows a logarithm-like function of oxidation times. It was used a theoretical model to predict the refractive index of the MCs that contains two components (Si and air) and tree component (Si, SiO₂, and air). Moreover, a photonic model was used to obtain the photonic band gap structure and the defect modes of different MCs in the UV-Visible range. The theoretical results showed that the experimental peaks within the UV photonic bandgap are indeed defect modes. Characterization of MCs was performed by SEM, FTIR and UV-Vis-NIR spectroscopy before and after the DOP. These results open the possibility to create silicon-based photonic structures within the UV range where usually silicon or porous silicon either strongly absorb or scatter light.

Structural, morphological and compositional characterizations of zinc selenide nanoparticles (NPs-ZnSe) are discussed in this work. NPs-ZnSe were obtained by colloidal synthesis in aqueous solution at room temperature, atmospheric pressure and without inert atmosphere. The synthesis was carried out using zinc chloride (ZnCl 2 ) and elemental selenium as precursors. A mix of Na 5 P 3 O 10 and NaOH called Extran was used as surfactant. Molar concentration and pH of the aqueous solution were varied to study their effect on the crystalline properties of the nanoparticles. The XRD measurements show that the NPs-ZnSe exhibits a cubic phase structure. The size of the nanocrystals was between 3 nm and 4.7 nm. HRTEM analysis showed that NPs-ZnSe exhibit semi-spherical shape. The presence of zinc and selenium in the NPs-ZnSe was confirmed through EDS measurements.

Physicochemical analysis was carried out to obtain the species distribution diagrams (SDDs) for the deposition of ZnO films as a function of OH− ion concentration ([OH−]) in the reaction solution. The study of SDDs predicts nucleation and ZnO film growth by means of the dominant species at a given pH value. To confirm this, a series of experiments were made varying the [OH−] in the reaction solution and keeping the others parameters constant. Structured zinc oxide (ZnO) films were obtained on glass substrates by microwave chemical bath deposition (MWCBD). Structural, optical and morphological ZnO film properties were investigated as a function of [OH−]. X-Ray diffraction technique (XRD) measurements show multiple diffraction peaks, indicating the polycrystalline nature of ZnO films. Scanning Electron Microscopy (SEM) images of ZnO structures showed morphological changes with the variation of [OH−]. The stoichiometry of the structures changed as the [OH−] was varied in solution. From Raman spectra, it was observed that the [OH−] of the reaction mixture strongly affects the crystal quality of ZnO structures. A reaction pathway for the synthesis of ZnO structures based on our results is proposed. Experimental results are consistent with the physical–chemical analysis.

In this work, we present the study of a strong white emission (3.35–1.72 eV) from non-stoichiometric silicon oxycarbide (SiCxOy) films deposited by hot filament chemical vapor deposition technique (HFCVD). For the growth of SiCxOy films, carbon and silicon oxide compounds in gas phase were generated from ethanol vapor and the chemical reaction of atomic hydrogen (H°) with a solid fused quartz source, respectively. To incorporate ethanol vapor to the reaction chamber, hydrogen flow was used as a carrier gas of ethanol molecules bubbled from liquid ethanol source. The analysis of composition obtained by X-ray photoelectron spectroscopy indicates that the carbon content in the SiCxOy films increases from 3.8 to 9.3 at.% as the carrier gas flow (H2) increases from 124 to 249 sccm, respectively. Fourier transform infra-red spectroscopy shows that the increase in carbon content favors the formation of both: Si–C bonds located at about 816 cm−1 and Si–O–Si vibrations located at around 1050-1070 cm−1 the last of which associates to a SiOx network. It is observed that SiCxOy films with carbon concentrations of 3.8 at.% emit a high photoluminescence (PL) intensity, however for carbon concentrations of 9.3 at.%, the PL intensity decreases. The analysis of luminescent centers indicates that high PL response could be associated to Si-related oxygen vacancies (Si-NOVs) and Si-related oxygen deficiency centers (Si-ODCs) due to low carbon concentration into the SiCxOy films.

The effect of magnesium doping in C60 films grown on mica was studied. An improvement on the conductivity of the films was observed when the concentration of magnesium was increased. Structural changes were also observed from the diffraction patterns of x-ray at high magnesium concentrations. A new peak in the photoconductivity spectra was observed. This new peak was also attributed to structural changes, which would lead to some changes in the carrier transport properties. The pentagonal pinch Ag(2) mode of the Raman spectra weakened and shifted to lower frequencies when the magnesium concentration increased, which indicates that the C60 molecule cage changed.

A comparative study of the synthesis of cadmium selenide (CdSe) nanoparticles (NPs) using different cadmium precursors such as, cadmium nitrate (Cd (NO3)2·4H2O), cadmium acetate ((CH3COO)2Cd·2H2O) and cadmium chloride (CdCl2·2.5H2O) is presented in this work. The method used to obtain the CdSe NPs was the colloidal synthesis at low temperature and atmospheric pressure. The Cd2+ ions were obtained in aqueous solution at room temperature, the surfactant used in the process was an aqueous solution of sodium hydroxide (NaOH), penta-sodium tripolyphosphate and H2O named commonly extran, which not only helps to stabilize the NPs, but also allows adjusting the pH of the solution. Se2- ions were obtained with sodium borohydride (NaBH4) as reductant at 75 oC. The by-products from the reaction were eliminated through a cleaning process with hydrochloric acid (HCl). Molar concentration of Cd:Se was varied from 3:1 to 1:3 and the pH value was varied between 8 and 11. The obtained samples were characterized by X-ray diffraction (XRD), it was seen that the obtained NPs present cubic centered face structure. The crystallite size from the powder was calculated using the Debye-Scherrer equation and was found between 3.3 nm and 5.6 nm, the variation in size depends on the molar concentration of cadmium and selenium. Morphological study was done using scanning electron microscopy (SEM) and compositional analysis was done by energy dispersive x-ray analysis (EDAX).

Unannealed GaN material was synthesized by pyrolysis from an organometallic complex, where after a nitridation process at 1000 °C in ammonia flow during 2 h, undoped GaN powders were obtained. X-ray diffraction pattern and Raman spectrum for unannealed GaN material did not show well-defined peaks. After the nitridation process, x-ray diffraction pattern and Raman spectrum, demonstrated defined peaks with reflection planes and vibration modes, characteristics of hexagonal GaN. Scanning electron microscopy showed an amorphous superficial morphology for both materials. On the other hand, energy dispersive spectroscopy showed a higher elemental contribution of oxygen for unannealed GaN material, with respect to undoped GaN powders. Photoluminescence spectrum for unannealed GaN material only showed an energy emission band at 1.8 eV (688 nm), while photoluminescence spectrum for undoped GaN powders demonstrated an emission with a maximum energy of 3.44 eV (360 nm), which was associated to the band-to-band transition for the hexagonal GaN.

Entangled Zn-ZnO nanorods and urchin-like microstructures were synthesized by the hot filament chemical vapor deposition technique at 825 and 1015°C, respectively. X-ray diffraction results showed a mixture of ZnO and Zn phases in both nanorods and urchin-like structures. The presence of Zn confirms the chemical dissociation of the ZnO solid source. The Z-ZnO nanorods with diameter of about 100 nm showed dispersed-like morphology. The urchin-like structures with micrometer diameters exhibited porous and rough morphology with epitaxial formation of nanorods.

This work presents a study of the evolution of the reflectance spectra of porous silicon as-growth and with thermal oxidation under controlled conditions. Porous silicon layers were prepared by electrochemical anodization of a silicon substrate p+ in an aqueous solution of hydrofluoric acid and ethanol. Multilayer structures were formed on the basis of porous silicon, two different layers were realized by controlling the refraction index of each one of the layers using the Bruggemann model, in this case for multilayer as-growth, and subsequently a dry oxidation was performed to observe the change in refractive index and reflectance. A model that contains the refractive index of silicon, air and silicon oxide is used for predicting the behavior of the reflectance spectra. With this model is possible to control the width of the reflectance spectrum of the band pass or also called Distributed Bragg Reflector (DBR), DBR were characterized and measured by SEM and UV-VIS spectroscopy. Reflectance spectra were obtained and we can see that the annealing provoked a shifted towards the ultra violet (UV). These changes on reflectance and refractive indexes indicate that oxidation processes can modify the multilayer porous silicon. The optical band gap energy (Eg) was obtained from 4.36 to 3.98 eV to the DBR. These low cost devices open the way to the development of optical sensing in UV entirely based on silicon.

In this work, the optical and electrical properties of simultaneously grown modulation-doped heterostructures (MDH) on (100)- and (631)-oriented GaAs substrates are investigated. Due to the amphoteric behavior of Si in AlGaAs doped films two dimensional electron (2DEG) and hole gas (2DHG) structures for the growth on (100) and (631) planes, respectively are obtained. Atomic force microscopy (AFM) revealed atomically flat surface for the (100)-MDH sample. On the contrary, (631)-MDH sustained uniform corrugation along [113] after the growth of the GaAs films, which provoked anisotropic mobility of the carriers at 77 K as confirmed by the Hall effect in a double arm bar. By photoluminescence spectroscopy (PL) the band to band transition, carbon and Si-related lines were identified. The concentration of the ternary alloy and impurities were evaluated by secondary ion mass spectrometry.