L.F. Marsal

Continuous analytic I-V model for surrounding-gate MOSFETs

We present a continuous analytic current-voltage (I-V) model for cylindrical undoped (lightly doped) surrounding gate (SGT) MOSFETs. It is based on the exact solution of the Poissons equation, and the current continuity equation without the charge-sheet approximation, allowing the inversion charge distribution in the silicon film to be adequately described. It is valid for all the operation regions (linear, saturation, subthreshold) and traces the transition between them without fitting parameters, being ideal for the kernel of SGT MOSFETs compact models. We have demonstrated that the I-V characteristics obtained by this model agree with three-dimensional numerical simulations for all ranges of gate and drain voltages.

Explicit continuous model for long-channel undoped surrounding gate MOSFETs

We present an analytical and continuous dc model for cylindrical undoped surrounding-gate (SGT) MOSFETs in which the channel current is written as an explicit function of the applied voltages. The model is based on a new unified charge control model developed for this device. The explicit model shows good agreement with the numerical exact solution obtained from the new charge control model, which was previously validated by comparison with three-dimensional numerical simulations.

Modeling of nanoscale gate-all-around MOSFETs

We present a compact physics-based model for the nanoscale gate-all-around MOSFET working in the ballistic limit. The current through the device is obtained by means of the Landauer approach, being the barrier height the key parameter in the model. The exact solution of the Poissons equation is obtained in order to deal with all the operation regions tracing properly the transitions between them.

Nanoporous Anodic Alumina Barcodes: Toward Smart Optical Biosensors

Toward a smart optical biosensor based on nanoporous anodic alumina (NAA): by modifying the pore geometry in nanoporous anodic alumina we are able to change the effective medium at will and tune the photoluminescence of NAA. The oscillations in the PL spectrum are converted into exclusive barcodes, which are useful for developing optical biomedical sensors in the UV-Visible region.

Unified compact model for the ballistic quantum wire and quantum well metal-oxide-semiconductor field-effect-transistor

We present a compact model based on the Landauer transmission theory for the silicon quantum wire and quantum well metal-oxide-semiconductor field effect transistor (MOSFET) working in the ballistic limit. This model captures the static current-voltage characteristics in all the operation regimes, below and above threshold voltage. The model provides a basic framework to account for the electronic transport in MOSFETs, being easily adaptable to gate structures such as the double-gate or gate-all-around. Numerical simulations based on the proposed model have been compared with experiments and quantum mechanical self-consistent simulations, with good agreement.

Structural and Optical Nanoengineering of Nanoporous Anodic Alumina Rugate Filters for Real-Time and Label-Free Biosensing Applications

In this study, we report about the structural engineering and optical optimization of nanoporous anodic alumina rugate filters (NAA-RFs) for real-time and label-free biosensing applications. Structurally engineered NAA-RFs are combined with reflection spectroscopy (RfS) in order to develop a biosensing system based on the position shift of the characteristic peak in the reflection spectrum of NAA-RFs (Δλpeak). This system is optimized and assessed by measuring shifts in the characteristic peak position produced by small changes in the effective medium (i.e., refractive index). To this end, NAA-RFs are filled with different solutions of d-glucose, and the Δλpeak is measured in real time by RfS. These results are validated by a theoretical model (i.e., the Looyenga-Landau-Lifshitz model), demonstrating that the control over the nanoporous structure makes it possible to optimize optical signals in RfS for sensing purposes. The linear range of these optical sensors ranges from 0.01 to 1.00 M, with a low detection limit of 0.01 M of d-glucose (i.e., 1.80 ppm), a sensitivity of 4.93 nm M(-1) (i.e., 164 nm per refractive index units), and a linearity of 0.998. This proof-of-concept study demonstrates that the proposed system combining NAA-RFs with RfS has outstanding capabilities to develop ultrasensitive, portable, and cost-competitive optical sensors.

Extraction of poly (3-hexylthiophene) (P3HT) properties from dark current voltage characteristics in a P3HT/n-crystalline-silicon solar cell

The dark current-voltage characteristics of poly (3-hexylthiophene) (P3HT)/n-type crystalline silicon solar cells were analyzed using an electrical equivalent circuit. We found that without illumination transport occurs due to hopping between localized states at the P3HT/silicon interface not only at low voltages, through multitunneling capture emission, but also at medium voltages, through tunneling-enhanced recombination. At high voltages the current is limited by series resistance and space-charge limited mechanisms. At low reverse voltages the current is limited by shunt resistance. From the temperature dependence of the equivalent circuit’s fitting parameters, we were able to estimate some physical parameters of the P3HT layer, namely the electron affinity, the charge carrier concentration and the characteristic temperature of the exponential trap distribution. The extracted P3HT values are in good agreement with previously reported values obtained using different methods but our approach takes into ...

Gold-coated ordered nanoporous anodic alumina bilayers for future label-free interferometric biosensors.

A cost-effective label-free optical biosensor based on gold-coated self-ordered nanoporous anodic alumina bilayers is presented. The structure is formed by two uniform nanoporous layers of different porosity (i.e., a top layer with large pores and a bottom layer with smaller pores). Each layer presents uniform pore size, regular pore distribution, and regular diameter along its pore length. To increase and improve the output sensing signals, a thin gold layer on the top surface was deposited. The gold layer increases the refractive index contrast between the nanoporous alumina layer and the analytical aqueous solution, and it results in a greater contrast in the interferometric spectrum and a higher sensitivity of the structure. From this structurally engineered architecture, the resulting reflectivity spectrum shows a complex series of Fabry-Pérot interference fringes, which was analyzed by the reflective interferometric Fourier transform spectroscopy (RIFTS) method. To determine the performance of this structure for biosensing applications, we tested bovine serum albumin (BSA) as the target protein. The results show a significant enhancement of the RIFTS peak intensity and position when a gold layer is on the top surface.

Porous silicon mirrors with enlarged omnidirectional band gap

Multilayers consisting of the periodic repetition of two layers with different refractive indices (nH and nL) may have an omnidirectional band gap, the width of which depends on the incidence medium and on the refractive index ratio nH∕nL. In porous silicon, this ratio is limited by the material and fabrication characteristics. This article makes a theoretical study of two multilayer structures in order to enlarge the omnidirectional band gap with the same refractive index ratio by varying only the thickness of the period. These structures are named balanced and unbalanced mirrors and consist of a few periodic multilayers stacked together. Porous silicon balanced and unbalanced mirrors with enlarged omnidirectional band gap for 1.55-μm applications are proposed. The results obtained with these mirror structures are compared with the results obtained with a chirped structure with the same characteristics.

ELECTRICAL CHARACTERIZATION OF N-AMORPHOUS/P-CRYSTALLINE SILICON HETEROJUNCTIONS

n‐type amorphous silicon on p‐type crystalline silicon heterojunction diodes were fabricated and electrically characterized. The a‐Si:H film was deposited by plasma enhanced chemical vapor deposition. Electrical properties were investigated by capacitance–voltage and current–voltage measurements at different temperatures. The capacitance–voltage results confirm an abrupt heterojunction. Current–voltage characteristics show good rectifying properties (50000:1 at ±0.5 V). A detailed analysis of transport mechanisms was developed in order to establish a unified model of conduction. Two carrier transport mechanisms are believed to be at the origin of the forward current. At low bias voltage (V<0.4 V), the current is determined by recombination at the amorphous side of the space charge region, while at higher voltages (V≳0.6 V), the current becomes space charge limited.