E. Comesaña

Simulation of the effect of p-layer properties on the electrical behaviour of a-Si:H thin film solar cells

Simulation data of the performance of amorphous silicon (a-Si:H) thin film solar cells using the software package Sentaurus TCAD (Synopsis Inc.) are presented. The Sentaurus software is configured with standard theoretical models describing e.g. the density of states in the mobility gap of a-Si:H, generation/recombination statistics, optical data of a-Si:H thin films etc. to calculate illuminated current voltage curves and the respective spectral response for the initial and degraded state of the solar cell. For the selected physical properties of the solar cell the simulation data predicts a maximum of the efficiency for an intrinsic a-Si:H layer thickness between 200–250 nm. Furthermore, a guideline for the optimization of the p-doped layer thickness and the doping concentration is given.

Three-dimensional simulations of random dopant and metal-gate workfunction variability in an In 0.53 Ga 0.47 As GAA MOSFET

We investigate the impacts of random dopant (RD) and gate workfunction variability on the subthreshold characteristics of a 50-nm-gate-length inversion-mode gate-all-around In0.53Ga0.47As MOSFET using a 3-D finite-element quantum-corrected drift-diffusion device simulator calibrated to experimental data. We have studied threshold voltage, off-current, and subthreshold slope variations. The workfunction variations on the subthreshold characteristics dominate and decrease with the reduction in grain diameter. The simulated grain diameters of 10, 7, and 5 nm exhibit threshold voltage standard deviations of 52, 41, and 27 mV, respectively. These values are larger than those observed in TiN-metal-gate Si FinFETs for a similar gate length. The impact of RD fluctuations is negligible when compared with bulk Si MOSFETs, giving a threshold voltage spread of only 6 mV.

Simulation of the temperature dependence of a-Si:H solar cell current-voltage characteristics

Simulation data of the performance of amorphous hydrogenated silicon (a-Si:H) thin film solar cells using the software package Sentaurus TCAD (Synopsis Inc) are presented. The Sentaurus software is configured with standard theoretical models describing e. g. the density of states in the mobility gap of a-Si:H, generation/recombination statistics, optical data of a-Si:H thin films, etc. to calculate illuminated current voltage curves and the respective spectral response for the initial and degraded state of solar cell. The study of the temperature dependence of the electrical parameters of solar cell is realized. The simulations results were compared with experimental data measured in T-Solar laboratory obtaining a good coincidence.

Influence of device geometry on electrical characteristics of a 10.7 nm SOI-FinFET

Several sources of variability such as imperfections during the manufacturing process, variations in critical dimensions (eg. oxide thickness, gate length), or intrinsic parameter fluctuations (eg. random dopants), influence the both device design and device and circuit performance. In this work, we have studied the impact of a shape of the device body on the characteristics of a 10.7 nm gate length SOI-FinFET. After a meticulous calibration against Monte-Carlo simulations, we have studied the effect of changing the shape of the body from a square cross-section to a triangular one on the sub-threshold region of the device. We have analysed four figures of merit: off-current, sub-threshold slope, threshold voltage and sub-threshold swing. The best results, in terms of lower off-current and sub-threshold swing, were obtained for the triangular shape device, which makes this particular geometry more suitable for digital applications.

Simulation of the tunnelling transport in ferromagnetic GaAs/ZnO heterojunctions

In this work we have implemented a numerical simulator and analytical model to study the dependence of the tunnelling current on the polarization ratio of the carrier spin for a degenerate and ferromagnetic heterojunction. We have applied these models to study the behaviour of a magnetically doped GaAs/ZnO PN junction and the current transport in a PN heterojunction where the polarization of the spin of the charge carriers is also a control variable.

Numerical simulation of a ferromagnetic spin-polarised diode

We present the first approach to a numerical simulator that extends the traditional resolution of the discrete Poisson and continuity equations, to solve a p-n ferromagnetic and degenerate junction. As it is degenerate, the carriers within the p-n junction can recombine through a direct tunnelling process from the valence band to the conduction band and viceversa. Ferromagnetism produces a spin split of the conduction band in n-type semiconductors and of the valence band in p-type semiconductors. The simulator evaluates the tunnelling asymmetry for an ideal junction with arbitrary spin polarisation on each side and computes how the current depends on the voltage across the junction. The obtained results predict that the strongest influence of the spin polarisation over the current value occurs in the negative resistance region, main characteristic of the tunnel diode.

Tunneling magnetoresistance dependence on the temperature in a ferromagnetic Zener diode

In the present work we focus on the study of the temperature dependence of the tunnelling current in a ferromagnetic Zener diode. We predict the tunneling magnetoresistance dependence on the temperature. Large doping concentrations lead to magnetic semiconductors with Curie temperature TC near or over room temperature and this will facilitate the introduction of new devices that make use of the ferromagnetism effects. A ccording to our calculations the tunneling magnetoresistance has the form TMR ∝ (TnC–Tn).

Raytracing and electromagnetic 2-D simulations of the EQE of a-Si:H thin-film solar cells

Thin-film amorphous silicon solar cells depend on light confinement techniques to improve their efficiency. The dual nature of light (wave-particle) compels the use of advanced simulation tools to model these optic phenomena. In the present research work we obtained the external quantum efficiency curve of a degraded cell following two methods: first considered light as a particle and subsequently, simulated it as a wave. The first case consisted of a Monte Carlo raytracing simulation, whereas in the second one we employed an electromagnetic wave finite-difference time-domain software, which solves thoroughly Maxwell equations. The fitting with the experimental is overall good with both procedures. Nonetheless, the interference effects can only be seen with the second tool.

A tool to deploy nanodevice simulations on cloud

The emerging of cloud computing has made it possible to deploy scientific applications in which users can manage the computational capacity on demand. In order to provide for the nanodevice researches the flexibility they require, we present in this paper the Flexible Cluster Manager (FCM), a tool that allows them to deploy Sentaurus TCAD virtual clusters on demand on cloud infrastructures by means of a web interface. The virtual clusters provided by FCM can be resized on-line, so adapting the computational capacity to the requirements of the researchers, which increase the reuse ratio of the computing resources. It is also possible to use it with other commercial or in-house simulator tools.

Design and Monte Carlo Simulation of a LED-Based Optic Coupler

The design of a multi-wavelength light source used to measure the external quantum efficiency of solar cells is presented. This low-cost optic coupler is based on the concept of integrating sphere and on the use of LEDs pulsing at different frequencies followed by a Fourier transformation of the current generated in the device under test. To obtain an accurate simulation model of the optic coupler experimental measurements were employed. Two algorithms based on Monte Carlo raytracing were tested. The first one uses a uniform random selection of the director angle and, depending on it, assigns a power to simulated rays. The second approach samples this angle randomly from a given distribution and uses an equal power for all rays. Both methods were compared in terms of their repeatability and dispersion.