J. Piqueras

Photoluminescence in transmutation doped liquid‐phase‐epitaxial gallium arsenide

Photoluminescence and Hall‐effect measurements on neutron transmutation doped liquid‐phase‐epitaxial GaAs layers were performed. The obtained results clearly point out that at least a part of the Ge atoms introduced by transmutation of Ga leave their original lattice site behaving as acceptors. The probable cause of these displacements are the recoils during γ and β emissions from the unstable Ga isotopes.

On the true optical properties of zinc nitride

Refractive index (n) and extinction coefficient (k) of Zn3N2 layers deposited by radio-frequency magnetron sputtering at temperatures (Ts) between 298 and 523 K were determined by spectroscopic ellipsometry. Results showed strong variations of the apparent optical constants with Ts and time attributed to surface effects. Resonant Rutherford backscattering and spectroscopic ellipsometry confirmed the formation of a ZnO surface layer provoked by the ambient exposure. Samples grown at low Ts presented the lowest surface roughness and exhibited 2.0 < n < 2.8 and 0.6 < k < 1.0 in the 1.5–4.5 eV energy range. The extracted n and k values accurately reproduced the reflectance properties.

Kinetics and Compositional Dependence on the Microwave Power and SiH4 / N 2 Flow Ratio of Silicon Nitride Deposited by Electron Cyclotron Resonance Plasmas

The archival version of this work was published in Journal of The Electrochemical Society. Hernandez, M. J., Garrido, J., Martinez, J. and J. Piqueras. Kinetics and compositional dependence on the microwave power and DiH4/N flow ratio of silicon nitride deposited by electron cyclotron resonance plasmas. Journal of The Electrochemical Society 141.11 (1994): 3234-3237

Excimer laser melting of GaAs: Real‐time optical study

In situ real‐time reflectivity measurements have been made in GaAs under ArF excimer laser (λ=193 nm) irradiation. The results obtained provide a reflectivity value for the solid material at the melting temperature of 0.44 and for the liquid of 0.63, both at 633 nm. The reflectivity values obtained for fluences just above the melting threshold (E=225 mJ/cm2) show that melting proceeds inhomogeneously, the near‐surface region being formed by a mixture of solid and liquid phases. The comparison of these results to those obtained previously for irradiation of single‐crystalline Si and Ge shows that inhomogeneous melting can be a general phenomenon at least in semiconductors. Higher fluences (E≳300 mJ/cm2) are necessary to induce an homogeneous melted layer on the surface of the irradiated material.

Gallium-assisted growth of silicon nanowires by electron cyclotron resonance plasmas

The use of gallium droplets for growing Si nanowires (SiNWs) by electron cyclotron resonance plasmas is investigated. First, the relationship between evaporation time and resultant size of the gallium droplets is studied. Through the use of spectroscopic ellipsometry, the dependence of the surface plasmon resonance (SPR) energy on the droplet size is determined. From these gallium droplets, SiNWs were grown at 300 and 550 °C in electron cyclotron resonance plasmas containing SiH(4), Ar, and H(2). Scanning electron microscopy results show that tapered NWs are obtained for a wide range of growth conditions. Besides, it is found that H(2) plays an important role in the parasitic axial growth of the SiNWs. Namely, H(2) inhibits the radial growth and contributes dramatically to increasing the SiNW defects.

Compositional and electrical properties of ECR-CVD silicon oxynitrides

Silicon oxynitride layers were deposited by electron cyclotron resonance (ECR) plasma enhanced chemical vapour deposition (PECVD). Oxygen, nitrogen and 5% argon diluted silane were used as precursors. The gas composition in the plasma was varied over a wide range to get compositions from pure to layers with around 20% O content. Large flow ratios are required to get significant N concentrations in the deposited layers. Pure layers could only be obtained when flow was completely suppressed. The infrared spectra of ECR are very similar to those of thermally grown oxides, but significant differences were found between the ECR and the high-temperature CVD spectra. MOS devices fabricated with these layers show that the interface state density increases from about to when the layer composition changes from pure to pure .

Glutathione immunosensing platform based on total internal reflection ellipsometry enhanced by functionalized gold nanoparticles.

An immunosensor to detect small molecules, such as glutathione (GSH), has been developed by combination of ellipsometry and Kretschmann surface plasmon resonance (SPR). The Au thin film used for surface plasmon polariton (SPP) excitation is functionalized with anti-GSH to specifically bind GSH. At low concentrations, the small refractive index changes caused by the low molecular weight of GSH induced only negligible shifts in the plasmon resonant energy during GSH binding. To improve sensitivity, gold nanoparticles (AuNPs) are functionalized with glutathione acting as amplifiers of the antigen-antibody interaction. Changes induced by the AuNP adsorption are monitored using Ψ and Δ ellipsometric functions. After performing competitive assays using solutions containing different concentrations of free GSH and a constant amount of functionalized AuNPs, it was concluded that the resonant energy linearly shifts as the relative concentration of free GSH increases. A detection limit for free GSH in the nanomolar range is found, demonstrating the effectiveness of AuNPs to enhance the sensitivity to immunoreactions in total internal reflection ellipsometry.

Laser melting of GaAs covered with thin metal layers

GaAs melting simulations with a pulsed ruby laser are reported. The presence of a thin metal layer deposited on the GaAs surface gives rise to a reduction in the melting threshold and to an increase of melted depths when compared with nude GaAs surfaces. Melting thresholds around 0.3 J/cm2 for nude GaAs surface and slightly below 0.25 J/cm2 for GaAs covered with a 120 Å tin layer are predicted in reasonable agreement with experimental results.

Atomic layer epitaxy of GaAs from tertiarybutylarsine and triethylgallium

GaAs growth by atomic layer epitaxy (ALE) from tertiarybutylarsine (TBA) and triethylgallium (TEG) in a chemical beam epitaxy (CBE) system is reported. A stable 4×8 surface reconstruction has been observed after Ga deposition at low substrate temperatures in the absence of TBA flux. The TEG reaction rate at the sample surface has been found to be lower under ALE conditions than under CBE growth conditions. No decay in the reflection high‐energy electron diffraction intensity was observed after the ALE growth of 700 monolayers of GaAs at 550 °C. Grown samples exhibit p‐type doping in the range of 1015 cm−3.

Thin film transistors based on zinc nitride as a channel layer for optoelectronic devices

Zinc nitride films were used as an active layer in thin film transistors to assess its performance in optoelectronic applications. Those nitride layers were grown by radio-frequency magnetron sputtering in Ar/N2 ambient using a Zn target. Bottom- and top-gate thin film transistors were fabricated by photolithography processes. Transmission measurements for these particular layers showed an absorption edge around 1.3 eV. Normally off transistor characteristics with a threshold voltage of 6 V were obtained in the bottom-gate configuration without post-growth annealing. In the saturation region, those transistors produced enhanced output characteristics under illumination with infrared/visible light.