Angel G Rodriguez - Profile on Academia.edu (original) (raw)
Papers by Angel G Rodriguez
Raman and FTIR Spectroscopy of GaSb and AlxGa1-xSb Alloys with Nanometric Thickness Grown at Low Temperatures by Liquid Phase Epitaxy
GaSb and AlxGa1-xSb thin layers were grown on (001) oriented GaSb substrates by liquid phase epit... more GaSb and AlxGa1-xSb thin layers were grown on (001) oriented GaSb substrates by liquid phase epitaxy technique at low temperatures. Until now, there are no previous reports on the growth of this alloy at temperatures lower than 400 °C. The layers were grown from 400 to 250 °C for the ternary layers, and at 200 °C for the binary layers using a supercooling process of 10 °C and a cooling rate of 0.5 °C/min. In addition to that, ternary AlxGa1-xSb layers were prepared at 250 °C for several contact times 1, 5, 10, 40 and 80 minutes, and something similar was done for binary GaSb layers, with contact times of 7.5, 15, 30, 60 and 120 minutes. Infrared reflectance results show the presence of single mode spectra for GaSb layers and two mode spectra for AlxGa1-xSb layers corroborating the growth of the alloys, whereas Raman scattering results show also the single and two mode behaviors of the GaSb and AlxGa1-xSb layers respectively. In ternary layers Raman bands, such as LO-GaSb like mode u...
Advanced Science, Engineering and Medicine, 2013
Single-walled carbon nanotubes (SWCNT) under high pressure have been studied by Raman spectroscop... more Single-walled carbon nanotubes (SWCNT) under high pressure have been studied by Raman spectroscopy. Considering cylindrical nanotubes with circular cross sections at all pressures the experimental data show an allometric pressure versus volume (PV) behavior under non-hydrostatic and quasi-hydrostatic conditions. We show that there is no need to consider a structural phase transition to explain the dependence of the radial breathing mode (RBM) phonon frequency with pressure. The bulk modulus (B o ) of the bundled nanotubes obtained from the PV data increases with pressure following a fit given by B o = 2.38 + 10.77P GPa.
Epitaxial single crystal films of Ge, with thickness from 0.2 to 2.4 µm, were grown on GaAs (001)... more Epitaxial single crystal films of Ge, with thickness from 0.2 to 2.4 µm, were grown on GaAs (001) by rf sputtering. These layers were characterized by High Resolution X-Ray Diffraction (HRXRD). Measured rocking curves show that pseudomorphic samples with good structural quality can be obtained by this growth technique. Asymmetrical reflections (115) and (-1-15) are used to determine the in-plane and in-growth lattice parameters of the grown films. From the behavior of these parameters and Ge diffraction peak broadening, with the layer thickness, an experimental value of 1.8 µm is obtained for the critical thickness of Ge grown on GaAs (001).
Journal of Crystal Growth, 2015
In x Ga 1 À x N (001) ternary alloys were grown on GaN/MgO (100) substrates in a plasma assisted ... more In x Ga 1 À x N (001) ternary alloys were grown on GaN/MgO (100) substrates in a plasma assisted molecular beam epitaxy system. We determined the in-plane [001] and in-growth [110] lattice parameters, as well as the bulk lattice parameter of the alloys for different In concentrations by high resolution X-ray diffraction. The In concentration was determined assuming Vegard's law for the alloy lattice parameter. The optical energy gap of In x Ga 1 À x N has been determined by transmittance measurements from absorption edges for several In concentrations. Our results show that the alloys have a direct band gap for all In concentrations and a bowing parameter b ¼ 1.84.
Physical Review B, 2001
Infrared reflection experiments were performed on wurtzite InN films with a range of free-electro... more Infrared reflection experiments were performed on wurtzite InN films with a range of free-electron concentrations grown by molecular-beam epitaxy. Measurements of the plasma edge frequencies were used to determine electron effective masses. The results show a pronounced increase in the electron effective mass with increasing electron concentration, indicating a nonparabolic conduction band in InN. We have also found a large Burstein-Moss shift of the fundamental band gap. The observed effects are quantitatively described by the k•p interaction within the two-band Kane model of narrow-gap semiconductors.
Synthetic Metals, 2010
One of the most used secondary dopants in thin film processing of PEDOT:PSS is dimethyl sulfoxide... more One of the most used secondary dopants in thin film processing of PEDOT:PSS is dimethyl sulfoxide (DMSO). In this work, we present results that explain, from the point of view of impedance spectroscopy, the mechanism of the increase in the conductivity observed on films based on PEDOT:PSS. The results obtained with this technique, combined with others such as AFM, and Raman and UV-vis-NIR spectroscopies, clearly show that there is a thinning of the insulating barrier of PSS surrounding conductive grains of PEDOT. It is shown that the thickness of the insulating barrier is related strongly and inversely with the onset frequency of AC conductivity. However, this is not the only existing effect, because for values beyond the optimal concentration of DMSO, we observe a decrease in the conductivity related with an increase of the separation of the PEDOT grains. The AC measurements and the AFM images also show the clear interplay between the increase of the PEDOT average grain size and the separation between them.
Applied Physics Letters, 2014
We present our measurements and model for the reflectancre anisotropy of the (001) surface of pol... more We present our measurements and model for the reflectancre anisotropy of the (001) surface of polar cubic zinc-blende semiconductor in the far infrared. We observe that the relative reflectance difference of both semi-insulating Cr-doped and the n-doped GaAs(001) can reach the value of twenty percents in the far infrared, which is two orders of magnitude higher than the reflectance difference
Thin Solid Films, 2011
The vibrational properties of Al 0.2 Ga 0.3 In 0.5 P:Be films grown on (100) GaAs substrates by s... more The vibrational properties of Al 0.2 Ga 0.3 In 0.5 P:Be films grown on (100) GaAs substrates by solid source molecular beam epitaxy varying the phosphorous cracking-zone temperature (PCT) were studied by Raman spectroscopy. The Raman-intensity ratio between the allowed longitudinal optical and the forbidden transverse optical (TO) phonons, and the full width at half maximum of their Lorentzian fits were used to characterize the crystalline quality of the films. The Raman spectra from the samples show changes in the shape and intensity of phonon resonances depending on the PCT variation, indicating that the disorder in the lattice increases with PCT. The increasing disorder is related to the inclusion of oxygen, which act as a non-intentional perturbing impurity in the lattice. In addition, a vibrational mode located at 598 cm − 1 related to a forbidden InP-like TO phonon resonance was correlated with oxygen-induced disorder. Photoluminescence at room temperature shows that the high inclusion of oxygen also deteriorates the optical properties of the samples, by introducing non-radiative recombination centers.
Spectroscopy Letters, 2014
We have examined the effect of high temperature on single-wall carbon nanotubes under air and nit... more We have examined the effect of high temperature on single-wall carbon nanotubes under air and nitrogen ambient by Raman spectroscopy. We observe the temperature dependence of the radial breathing mode and the G-band modes. The thermal expansion coefficient (b) of the bundled nanotubes is obtained experimentally using the estimated volume from Raman scattering. b behaves linearly with temperature from 0.33 Â 10 À5 K À1 to 0.28 Â 10 À5 K À1 in air and from 0.58 Â 10 À5 K À1 to 0.47 Â 10 À5 K À1 in nitrogen ambient, respectively. The temperature dependence of the radial breathing mode Raman frequencies is consistent with a pure temperature effect.
Giant reflectance anisotropy of polar cubic semiconductors in the far infrared
physica status solidi (c), 2003
ABSTRACT We present our measurements and model for the reflectancre anisotropy of the (001) surfa... more ABSTRACT We present our measurements and model for the reflectancre anisotropy of the (001) surface of polar cubic zinc-blende semiconductor in the far infrared. We observe that the relative reflectance difference of GaAs(001) in the far infrared can reach the value of twenty percents which is two orders of magnitude higher than the reflectance difference of the GaAs(001) in the near-ultraviolet - visible range. The most strong reflectance anisotropy was observed in the optical phonon Reststrahlbande and its vicinity. We relate the observed reflectance anisotropy with the anisotropy of the optical-phonon and plasma damping constants. Such anisotropy can be caused by anisotropic inhomogeneous broadening of the frequencies of the optical-phonon and plasma oscillations polarized respectively along the [110] and directions. This effect can be understood in terms of the lattice-deformation-induced changes of the optical-phonon force constants and electron-effective-mass tensor components. Anisotropic inhomogeneous strain of the lattice can in turn be induced by anisotropic microscopic short-range ordering of point defects (dopants) and dislocations in near-surface regions of noncentrosymmentric zinc-blende semiconductors. The observed giant reflectance anisotropy can be used as a sensitive tool for the far infrared characterization of zinc-blende semiconductors. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Microelectronics Journal, 2003
Modulation-doped GaAs/AlGaAs heterostructures have been studied by photoreflectance spectroscopy.... more Modulation-doped GaAs/AlGaAs heterostructures have been studied by photoreflectance spectroscopy. The spectra at room temperature show Franz -Keldysh oscillations associated to the substrate -buffer layer interface. The built-in electric field magnitude calculated from these oscillations is related with the two-dimensional electron gas (2DEG) mobility. In addition we observed two signals associated to the GaAs capping layer and to the 2DEG, respectively. q
Journal of Non-Crystalline Solids, 2009
Low energy shifted photoluminescence from isolated erbium ions incorporated into a-SiGe:H thin fi... more Low energy shifted photoluminescence from isolated erbium ions incorporated into a-SiGe:H thin films is reported. The Er 3+ are thermally diffused from an a-SiGe:H:Er layer to a-SiGe:H subsequently grown, both by magnetron sputtering. The photoluminescence observed is associated with transitions produced by erbium emission centers activated by the oxidation in a 1 h annealing process in air at 250°C. The resultant Er 3+ concentration observed from the a-SiGe:H is affected by the hydrogen concentration already present in the layer. It is observed that at higher hydrogen concentrations in a-SiGe:H the resultant amount of diffused Er 3+ decreases. As a consequence of the resultant smaller density of erbium ions, the probability of having isolated Er 3+ ions increases. In this last regime, a correlation with stronger photoluminescence is observed.
Polarized Raman spectroscopy of corrugated MBE grown GaAs (6̄3̄1̄) homoepitaxial films
Journal of Crystal Growth, 2013
ABSTRACT In this work, we present a Raman scattering study of GaAs layers grown on (6̄3̄1̄)-orien... more ABSTRACT In this work, we present a Raman scattering study of GaAs layers grown on (6̄3̄1̄)-oriented substrates by molecular beam epitaxy. A set of samples whose morphology sustained different corrugation order were grown by MBE by varying the growth parameters such as temperature and As/Ga flux ratio. We employed polarized Raman spectroscopy using the backscattering configurations Z(XX) , Z(XY) and Z(YY) . According to the calculated dipole selection rules both TO and LO phonons are allowed for backscattering from a perfect GaAs (6̄3̄1̄) crystal, but with the intensity of the TO phonon much larger than that of the LO phonon. However, it is found that the selection rules differ for corrugated samples. Besides, the TO/LO phonon resonances intensity ratio and the LO peak asymmetry depend on the corrugation order of the samples.
Journal of Crystal Growth, 2009
High-resolution X-ray diffraction analysis of AlxGa1−xN/InxGa1−xN/GaN on sapphire multilayer stru... more High-resolution X-ray diffraction analysis of AlxGa1−xN/InxGa1−xN/GaN on sapphire multilayer structures: Theoretical, simulations, and experimental observations
Journal of Crystal Growth, 2007
GaAs layers were grown by MBE on (6 3 1)-oriented substrates under a variety of growth conditions... more GaAs layers were grown by MBE on (6 3 1)-oriented substrates under a variety of growth conditions. The structural properties of the samples were studied by atomic force microscopy and micro-Raman spectroscopy. Hillock structures were formed on the layers surface presenting an elongation towards the ½5; 9; 3 direction, with dimensions and density that depend on the growth conditions. Raman spectra from the samples showed two peaks corresponding to transversal (TO)-and longitudinal (LO) optical phonons. According to the calculated dipole selection rules both TO and LO phonons are allowed for backscattering from a perfect GaAs(6 3 1) surface, but with the intensity of the TO phonon much larger than that of the LO phonon. This result was used to study the changes in the GaAs surface morphology as a function of growth time and growth temperature. By employing a relatively high growth temperature and a high As pressure a surface corrugation was formed which could be used for the synthesis of one-dimensional structures. r 2006 Published by Elsevier B.V.
Journal of Crystal Growth, 2007
The optical properties of Be-doped Al 0.2 Ga 0.3 In 0.5 P layers grown on GaAs by solid source mo... more The optical properties of Be-doped Al 0.2 Ga 0.3 In 0.5 P layers grown on GaAs by solid source molecular beam epitaxy have been studied. In particular, we investigated a set of heavy doped samples grown at different phosphorous cracking temperatures (PCT). The analysis of the 15 K-PL spectra showed three strong transitions below the AlGaInP band edge associated to Be acceptor levels (A 0 , X), shallow impurities (A, X) and a broad signal related with oxygen deep levels (O, DL). The Photoluminescence (PL) spectra from samples dramatically change as the PCT is increased, in such a way that in the spectrum from the sample grown at the highest P-cracking zone temperature, the (O, DL) intensity is visibly dominant. Besides, we found that despite that the Be cell temperature being maintained at 1015 1C for all the samples, the Be-doping concentration is reduced as the PCT is increased. Therefore, as PCT increases, the active Beconcentration decreases as a consequence of Be-compensation with O. This phenomena is reflected in the PL properties of the samples as a reduction of the (A 0 , X) intensity. The rocking curves of the (0 0 4) planes obtained by high resolution X-ray diffraction (HRXRD) justify the inclusion of impurities and the reduction of the crystal quality of the sample grown at the highest PCT. This work shows that the incorporation of defects during the growth of the AlGaInP:Be films due to O contamination can be reduced using low PCT. r
![Research paper thumbnail of In-plane and out-of-plane lattice parameters of [11n] epitaxial strained layers](https://attachments.academia-assets.com/46452775/thumbnails/1.jpg)
](Journal of Crystal Growth, 2006
A procedure is proposed to determine the in-plane (a || ) and out-of-plane (a ? ) lattice paramet... more A procedure is proposed to determine the in-plane (a || ) and out-of-plane (a ? ) lattice parameters of ½1 1 n epitaxial cubic strained layers by high resolution X-ray diffraction (HRXRD) rocking curves (RC). The common approach followed to obtain the lattice parameters from asymmetrical diffraction RC of ½0 0 1 grown films, is extended to apply it to ½1 1 n grown layers. Epitaxial pseudomorphic Ge layers were grown on ½0 0 1, ½1 1 0, ½1 1 1, ½1 1 2, ½1 1 3 and ½1 1 4 GaAs substrates to analyze them by HRXRD. Reciprocal space maps (RSM) were also measured to obtain the lattice parameters of these samples. We observe an excellent agreement of the RC and RSM results, which demonstrates the validity of the suggested RC approach. r
[sub x] alloys epitaxially grown on GaAs](https://attachments.academia-assets.com/46452757/thumbnails/1.jpg)
](Journal of Applied Physics, 2001
͑GaAs͒ 1Ϫx ͑Si 2 ) x metastable alloys grown on ͑001͒, ͑110͒, ͑112͒, and ͑111͒ GaAs substrates, w... more ͑GaAs͒ 1Ϫx ͑Si 2 ) x metastable alloys grown on ͑001͒, ͑110͒, ͑112͒, and ͑111͒ GaAs substrates, with Si fractions in the range 0рxр0.43, were studied by Raman scattering. Two modes near the LO and TO modes of GaAs, besides two local modes associated either with Si-As or Si-Ga and Si-Si bonds, are observed in the Raman spectra. The ratio of integrated intensities of TO-like and LO-like modes (I TO /I LO ) is used to evaluate the short range order. It is observed that the zinc blende to diamond transition reported in the literature for these alloys does not influence the Si fraction dependence of the short range order.
Raman and FTIR Spectroscopy of GaSb and AlxGa1-xSb Alloys with Nanometric Thickness Grown at Low Temperatures by Liquid Phase Epitaxy
GaSb and AlxGa1-xSb thin layers were grown on (001) oriented GaSb substrates by liquid phase epit... more GaSb and AlxGa1-xSb thin layers were grown on (001) oriented GaSb substrates by liquid phase epitaxy technique at low temperatures. Until now, there are no previous reports on the growth of this alloy at temperatures lower than 400 °C. The layers were grown from 400 to 250 °C for the ternary layers, and at 200 °C for the binary layers using a supercooling process of 10 °C and a cooling rate of 0.5 °C/min. In addition to that, ternary AlxGa1-xSb layers were prepared at 250 °C for several contact times 1, 5, 10, 40 and 80 minutes, and something similar was done for binary GaSb layers, with contact times of 7.5, 15, 30, 60 and 120 minutes. Infrared reflectance results show the presence of single mode spectra for GaSb layers and two mode spectra for AlxGa1-xSb layers corroborating the growth of the alloys, whereas Raman scattering results show also the single and two mode behaviors of the GaSb and AlxGa1-xSb layers respectively. In ternary layers Raman bands, such as LO-GaSb like mode u...
Advanced Science, Engineering and Medicine, 2013
Single-walled carbon nanotubes (SWCNT) under high pressure have been studied by Raman spectroscop... more Single-walled carbon nanotubes (SWCNT) under high pressure have been studied by Raman spectroscopy. Considering cylindrical nanotubes with circular cross sections at all pressures the experimental data show an allometric pressure versus volume (PV) behavior under non-hydrostatic and quasi-hydrostatic conditions. We show that there is no need to consider a structural phase transition to explain the dependence of the radial breathing mode (RBM) phonon frequency with pressure. The bulk modulus (B o ) of the bundled nanotubes obtained from the PV data increases with pressure following a fit given by B o = 2.38 + 10.77P GPa.
Epitaxial single crystal films of Ge, with thickness from 0.2 to 2.4 µm, were grown on GaAs (001)... more Epitaxial single crystal films of Ge, with thickness from 0.2 to 2.4 µm, were grown on GaAs (001) by rf sputtering. These layers were characterized by High Resolution X-Ray Diffraction (HRXRD). Measured rocking curves show that pseudomorphic samples with good structural quality can be obtained by this growth technique. Asymmetrical reflections (115) and (-1-15) are used to determine the in-plane and in-growth lattice parameters of the grown films. From the behavior of these parameters and Ge diffraction peak broadening, with the layer thickness, an experimental value of 1.8 µm is obtained for the critical thickness of Ge grown on GaAs (001).
Journal of Crystal Growth, 2015
In x Ga 1 À x N (001) ternary alloys were grown on GaN/MgO (100) substrates in a plasma assisted ... more In x Ga 1 À x N (001) ternary alloys were grown on GaN/MgO (100) substrates in a plasma assisted molecular beam epitaxy system. We determined the in-plane [001] and in-growth [110] lattice parameters, as well as the bulk lattice parameter of the alloys for different In concentrations by high resolution X-ray diffraction. The In concentration was determined assuming Vegard's law for the alloy lattice parameter. The optical energy gap of In x Ga 1 À x N has been determined by transmittance measurements from absorption edges for several In concentrations. Our results show that the alloys have a direct band gap for all In concentrations and a bowing parameter b ¼ 1.84.
Physical Review B, 2001
Infrared reflection experiments were performed on wurtzite InN films with a range of free-electro... more Infrared reflection experiments were performed on wurtzite InN films with a range of free-electron concentrations grown by molecular-beam epitaxy. Measurements of the plasma edge frequencies were used to determine electron effective masses. The results show a pronounced increase in the electron effective mass with increasing electron concentration, indicating a nonparabolic conduction band in InN. We have also found a large Burstein-Moss shift of the fundamental band gap. The observed effects are quantitatively described by the k•p interaction within the two-band Kane model of narrow-gap semiconductors.
Synthetic Metals, 2010
One of the most used secondary dopants in thin film processing of PEDOT:PSS is dimethyl sulfoxide... more One of the most used secondary dopants in thin film processing of PEDOT:PSS is dimethyl sulfoxide (DMSO). In this work, we present results that explain, from the point of view of impedance spectroscopy, the mechanism of the increase in the conductivity observed on films based on PEDOT:PSS. The results obtained with this technique, combined with others such as AFM, and Raman and UV-vis-NIR spectroscopies, clearly show that there is a thinning of the insulating barrier of PSS surrounding conductive grains of PEDOT. It is shown that the thickness of the insulating barrier is related strongly and inversely with the onset frequency of AC conductivity. However, this is not the only existing effect, because for values beyond the optimal concentration of DMSO, we observe a decrease in the conductivity related with an increase of the separation of the PEDOT grains. The AC measurements and the AFM images also show the clear interplay between the increase of the PEDOT average grain size and the separation between them.
Applied Physics Letters, 2014
We present our measurements and model for the reflectancre anisotropy of the (001) surface of pol... more We present our measurements and model for the reflectancre anisotropy of the (001) surface of polar cubic zinc-blende semiconductor in the far infrared. We observe that the relative reflectance difference of both semi-insulating Cr-doped and the n-doped GaAs(001) can reach the value of twenty percents in the far infrared, which is two orders of magnitude higher than the reflectance difference
Thin Solid Films, 2011
The vibrational properties of Al 0.2 Ga 0.3 In 0.5 P:Be films grown on (100) GaAs substrates by s... more The vibrational properties of Al 0.2 Ga 0.3 In 0.5 P:Be films grown on (100) GaAs substrates by solid source molecular beam epitaxy varying the phosphorous cracking-zone temperature (PCT) were studied by Raman spectroscopy. The Raman-intensity ratio between the allowed longitudinal optical and the forbidden transverse optical (TO) phonons, and the full width at half maximum of their Lorentzian fits were used to characterize the crystalline quality of the films. The Raman spectra from the samples show changes in the shape and intensity of phonon resonances depending on the PCT variation, indicating that the disorder in the lattice increases with PCT. The increasing disorder is related to the inclusion of oxygen, which act as a non-intentional perturbing impurity in the lattice. In addition, a vibrational mode located at 598 cm − 1 related to a forbidden InP-like TO phonon resonance was correlated with oxygen-induced disorder. Photoluminescence at room temperature shows that the high inclusion of oxygen also deteriorates the optical properties of the samples, by introducing non-radiative recombination centers.
Spectroscopy Letters, 2014
We have examined the effect of high temperature on single-wall carbon nanotubes under air and nit... more We have examined the effect of high temperature on single-wall carbon nanotubes under air and nitrogen ambient by Raman spectroscopy. We observe the temperature dependence of the radial breathing mode and the G-band modes. The thermal expansion coefficient (b) of the bundled nanotubes is obtained experimentally using the estimated volume from Raman scattering. b behaves linearly with temperature from 0.33 Â 10 À5 K À1 to 0.28 Â 10 À5 K À1 in air and from 0.58 Â 10 À5 K À1 to 0.47 Â 10 À5 K À1 in nitrogen ambient, respectively. The temperature dependence of the radial breathing mode Raman frequencies is consistent with a pure temperature effect.
Giant reflectance anisotropy of polar cubic semiconductors in the far infrared
physica status solidi (c), 2003
ABSTRACT We present our measurements and model for the reflectancre anisotropy of the (001) surfa... more ABSTRACT We present our measurements and model for the reflectancre anisotropy of the (001) surface of polar cubic zinc-blende semiconductor in the far infrared. We observe that the relative reflectance difference of GaAs(001) in the far infrared can reach the value of twenty percents which is two orders of magnitude higher than the reflectance difference of the GaAs(001) in the near-ultraviolet - visible range. The most strong reflectance anisotropy was observed in the optical phonon Reststrahlbande and its vicinity. We relate the observed reflectance anisotropy with the anisotropy of the optical-phonon and plasma damping constants. Such anisotropy can be caused by anisotropic inhomogeneous broadening of the frequencies of the optical-phonon and plasma oscillations polarized respectively along the [110] and directions. This effect can be understood in terms of the lattice-deformation-induced changes of the optical-phonon force constants and electron-effective-mass tensor components. Anisotropic inhomogeneous strain of the lattice can in turn be induced by anisotropic microscopic short-range ordering of point defects (dopants) and dislocations in near-surface regions of noncentrosymmentric zinc-blende semiconductors. The observed giant reflectance anisotropy can be used as a sensitive tool for the far infrared characterization of zinc-blende semiconductors. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Microelectronics Journal, 2003
Modulation-doped GaAs/AlGaAs heterostructures have been studied by photoreflectance spectroscopy.... more Modulation-doped GaAs/AlGaAs heterostructures have been studied by photoreflectance spectroscopy. The spectra at room temperature show Franz -Keldysh oscillations associated to the substrate -buffer layer interface. The built-in electric field magnitude calculated from these oscillations is related with the two-dimensional electron gas (2DEG) mobility. In addition we observed two signals associated to the GaAs capping layer and to the 2DEG, respectively. q
Journal of Non-Crystalline Solids, 2009
Low energy shifted photoluminescence from isolated erbium ions incorporated into a-SiGe:H thin fi... more Low energy shifted photoluminescence from isolated erbium ions incorporated into a-SiGe:H thin films is reported. The Er 3+ are thermally diffused from an a-SiGe:H:Er layer to a-SiGe:H subsequently grown, both by magnetron sputtering. The photoluminescence observed is associated with transitions produced by erbium emission centers activated by the oxidation in a 1 h annealing process in air at 250°C. The resultant Er 3+ concentration observed from the a-SiGe:H is affected by the hydrogen concentration already present in the layer. It is observed that at higher hydrogen concentrations in a-SiGe:H the resultant amount of diffused Er 3+ decreases. As a consequence of the resultant smaller density of erbium ions, the probability of having isolated Er 3+ ions increases. In this last regime, a correlation with stronger photoluminescence is observed.
Polarized Raman spectroscopy of corrugated MBE grown GaAs (6̄3̄1̄) homoepitaxial films
Journal of Crystal Growth, 2013
ABSTRACT In this work, we present a Raman scattering study of GaAs layers grown on (6̄3̄1̄)-orien... more ABSTRACT In this work, we present a Raman scattering study of GaAs layers grown on (6̄3̄1̄)-oriented substrates by molecular beam epitaxy. A set of samples whose morphology sustained different corrugation order were grown by MBE by varying the growth parameters such as temperature and As/Ga flux ratio. We employed polarized Raman spectroscopy using the backscattering configurations Z(XX) , Z(XY) and Z(YY) . According to the calculated dipole selection rules both TO and LO phonons are allowed for backscattering from a perfect GaAs (6̄3̄1̄) crystal, but with the intensity of the TO phonon much larger than that of the LO phonon. However, it is found that the selection rules differ for corrugated samples. Besides, the TO/LO phonon resonances intensity ratio and the LO peak asymmetry depend on the corrugation order of the samples.
Journal of Crystal Growth, 2009
High-resolution X-ray diffraction analysis of AlxGa1−xN/InxGa1−xN/GaN on sapphire multilayer stru... more High-resolution X-ray diffraction analysis of AlxGa1−xN/InxGa1−xN/GaN on sapphire multilayer structures: Theoretical, simulations, and experimental observations
Journal of Crystal Growth, 2007
GaAs layers were grown by MBE on (6 3 1)-oriented substrates under a variety of growth conditions... more GaAs layers were grown by MBE on (6 3 1)-oriented substrates under a variety of growth conditions. The structural properties of the samples were studied by atomic force microscopy and micro-Raman spectroscopy. Hillock structures were formed on the layers surface presenting an elongation towards the ½5; 9; 3 direction, with dimensions and density that depend on the growth conditions. Raman spectra from the samples showed two peaks corresponding to transversal (TO)-and longitudinal (LO) optical phonons. According to the calculated dipole selection rules both TO and LO phonons are allowed for backscattering from a perfect GaAs(6 3 1) surface, but with the intensity of the TO phonon much larger than that of the LO phonon. This result was used to study the changes in the GaAs surface morphology as a function of growth time and growth temperature. By employing a relatively high growth temperature and a high As pressure a surface corrugation was formed which could be used for the synthesis of one-dimensional structures. r 2006 Published by Elsevier B.V.
Journal of Crystal Growth, 2007
The optical properties of Be-doped Al 0.2 Ga 0.3 In 0.5 P layers grown on GaAs by solid source mo... more The optical properties of Be-doped Al 0.2 Ga 0.3 In 0.5 P layers grown on GaAs by solid source molecular beam epitaxy have been studied. In particular, we investigated a set of heavy doped samples grown at different phosphorous cracking temperatures (PCT). The analysis of the 15 K-PL spectra showed three strong transitions below the AlGaInP band edge associated to Be acceptor levels (A 0 , X), shallow impurities (A, X) and a broad signal related with oxygen deep levels (O, DL). The Photoluminescence (PL) spectra from samples dramatically change as the PCT is increased, in such a way that in the spectrum from the sample grown at the highest P-cracking zone temperature, the (O, DL) intensity is visibly dominant. Besides, we found that despite that the Be cell temperature being maintained at 1015 1C for all the samples, the Be-doping concentration is reduced as the PCT is increased. Therefore, as PCT increases, the active Beconcentration decreases as a consequence of Be-compensation with O. This phenomena is reflected in the PL properties of the samples as a reduction of the (A 0 , X) intensity. The rocking curves of the (0 0 4) planes obtained by high resolution X-ray diffraction (HRXRD) justify the inclusion of impurities and the reduction of the crystal quality of the sample grown at the highest PCT. This work shows that the incorporation of defects during the growth of the AlGaInP:Be films due to O contamination can be reduced using low PCT. r
Journal of Crystal Growth, 2006
A procedure is proposed to determine the in-plane (a || ) and out-of-plane (a ? ) lattice paramet... more A procedure is proposed to determine the in-plane (a || ) and out-of-plane (a ? ) lattice parameters of ½1 1 n epitaxial cubic strained layers by high resolution X-ray diffraction (HRXRD) rocking curves (RC). The common approach followed to obtain the lattice parameters from asymmetrical diffraction RC of ½0 0 1 grown films, is extended to apply it to ½1 1 n grown layers. Epitaxial pseudomorphic Ge layers were grown on ½0 0 1, ½1 1 0, ½1 1 1, ½1 1 2, ½1 1 3 and ½1 1 4 GaAs substrates to analyze them by HRXRD. Reciprocal space maps (RSM) were also measured to obtain the lattice parameters of these samples. We observe an excellent agreement of the RC and RSM results, which demonstrates the validity of the suggested RC approach. r
Journal of Applied Physics, 2001
͑GaAs͒ 1Ϫx ͑Si 2 ) x metastable alloys grown on ͑001͒, ͑110͒, ͑112͒, and ͑111͒ GaAs substrates, w... more ͑GaAs͒ 1Ϫx ͑Si 2 ) x metastable alloys grown on ͑001͒, ͑110͒, ͑112͒, and ͑111͒ GaAs substrates, with Si fractions in the range 0рxр0.43, were studied by Raman scattering. Two modes near the LO and TO modes of GaAs, besides two local modes associated either with Si-As or Si-Ga and Si-Si bonds, are observed in the Raman spectra. The ratio of integrated intensities of TO-like and LO-like modes (I TO /I LO ) is used to evaluate the short range order. It is observed that the zinc blende to diamond transition reported in the literature for these alloys does not influence the Si fraction dependence of the short range order.