Stéphane Biondo

Optical-electrical simulation of organic solar cells: excitonic modeling parameter influence on electrical characteristics

This paper deals with Organic Solar Cells (OSCs) simulation using finite element method. Optical modeling is performed via Finite Difference Time Domain method whereas the continuity and Poisson’s equations are solved to obtain electrical characteristics of the OSC. In this work, simulation results point out the influence of physical parameters such as the exciton diffusion coefficient or the exciton lifetime on OSC performances. The comparison of modeling results and experimental measurement allows the exciton recombination, dissociation rate and lifetime to be determinated.

Optical-electrical simulation of organic solar cells: Influence of light trapping by photonic crystal and ZnO spacer on electrical characteristics

This paper deals with organic solar cells (OSC) simulation using finite element method. Optical modeling is performed via finite difference time domain method whilst the continuity and Poisson’s equations are solved to obtain electrical characteristics of the OSC. In this work, simulation results point out the OSC structure influence on its performances, either by the interface grating or by the ZnO optical spacer introduced between the active layer (P3HT:PCBM layer) and the metallic electrode. The comparison of modeling results and experimental measurement allows us to confirm and forecast the enhancement of the photovoltaic properties such as the power conversion efficiency.

Influence of Heating and Cooling Rates of Post-Implantation Annealing Process on Al-Implanted 4H-SiC Epitaxial Samples

We report on topographical, structural and electrical measurements of aluminum-implanted and annealed 4H-SiC epitaxial samples. The influence of heating-up and cooling-down temperature rates on the SiC surface roughness, the crystal volume reordering and the dopant electrical activation was particularly studied. A higher heating-rate was found to preserve the rms roughness for annealing temperatures lower than 1700°C, and to improve the sheet resistance whatever the annealing temperature due to a better dopant activation (except for 1600°C process, which induced a dark zone in the sample volume). A complete activation was calculated for an annealing at 1700°C during 30 minutes, with a ramp-up at 20°C/s. Rising the cooling-down rate appeared to increase the sheet resistance, probably due to a higher concentration of point defects in the implanted layer.

Influence on electrical characteristics of the design of 4H-SiC ultraviolet photodetectors: Theoretical analysis and simulations

This paper deals with the simulation of the reverse current density of 4H-SiC ultraviolet- (UV) photodetector devices based on p-i-n diodes. Simulations using the finite-element method presented in this paper lead to an understanding of the photodetector current density levels in dark field, as well as under UV exposure. The theoretical study coming from these simulations allows us to propose some UV-photodetector performance enhancements. A way to improve the UV-photodetector performance is to increase the current density at reverse bias. This study demonstrates the improvement in electrical characteristics achievable by either optical or electrical means. Optical simulations prove that an increase in photon harvesting is possible by using a specific patterned surface, a surface grating which behaves as a photonic crystal. In addition to the absorption enhancement achieved caused by this kind of surface, we point out wavelength selectivity. Nevertheless, the electrical simulation confirms that the electr...

Effect of Helium implantation on gettering and electrical properties of 4H‐SiC epilayers

This paper tests the gettering ability of sites created by He implantation in 4H‐SiC while heating the sample or not, and their impact on carrier lifetime. The spatial distribution of implantation‐induced defects (cavities, stacking faults and dislocations) is studied by transmission electron microscopy (TEM) and is compared to gold profiles performed by Rutherford Backscattering (RBS) in samples intentionally contaminated with gold. Minority carrier lifetimes are also measured with a specific set‐up based on microwave photoconductivity decay (μ‐PCD). Though gold atoms do not seem to be efficiently trapped by cavities, the presence of dislocations is of major importance to monitor gold diffusion. Indeed, they can double both its level and its diffusion length in the bulk. Gold is assumed to diffuse faster along dislocation cores. Besides, the implantation‐related defects are found to improve the carrier lifetime in the material, but the role of He2+ left in cavities remains to be investigated.This paper tests the gettering ability of sites created by He implantation in 4H‐SiC while heating the sample or not, and their impact on carrier lifetime. The spatial distribution of implantation‐induced defects (cavities, stacking faults and dislocations) is studied by transmission electron microscopy (TEM) and is compared to gold profiles performed by Rutherford Backscattering (RBS) in samples intentionally contaminated with gold. Minority carrier lifetimes are also measured with a specific set‐up based on microwave photoconductivity decay (μ‐PCD). Though gold atoms do not seem to be efficiently trapped by cavities, the presence of dislocations is of major importance to monitor gold diffusion. Indeed, they can double both its level and its diffusion length in the bulk. Gold is assumed to diffuse faster along dislocation cores. Besides, the implantation‐related defects are found to improve the carrier lifetime in the material, but the role of He2+ left in cavities remains to be investigated.

4H-SiC P+N UV Photodiodes : A Comparison between Beam and Plasma Doping Processes

This paper presents a study of 4H-SiC UV photodetectors based on p+n thin junctions. Two kinds of p+ layers have been implemented, aiming at studying the influence of the junction elaborated by the ion implantation process (and the subsequent annealing) on the device characteristics. Aluminum and Boron dopants have been introduced by beam line and by plasma ion implantation, respectively. Dark currents are lower with Al-implanted diodes (2 pA/cm2 @ - 5 V). Accordingly to simulation results concerning the influence of the junction thickness and doping, plasma B-implanted diodes give rise to the best sensitivity values (1.5x10-1 A/W @ 330 nm).

Optical and Electrical Simulation of 4H-SiC UV Photodetector by Finite Element Method

This paper focuses on UV-photodetector simulation. The calculus method description and the physical equations which occur in this model are presented as well as the UV-photodetector structure (p+n--n+ diode). Based on the Finite Element Method the electrical part solves the continuity and Poisson equation, and the optical part solves by Maxwell’s equation, FDTD [1]. Simulation works point out the influence of the p+-type layer on the electrical characteristics such as the current densities versus reverse bias. Indeed, simulation results show the current density increase with the decrease doping concentration or the p+-type layer thickness.

SiC-based neutron detector in quasi-realistic working conditions: Efficiency and stability at room and high temperature under fast neutron irradiations

In the framework of the European I_SMART project, we have designed and made new SiC-based nuclear radiation detectors able to operate in harsh environments and to detect both fast and thermal neutrons. In this paper, we report experimental results of fast neutron irradiation campaign at high temperature (106 °C) in quasi-realistic working conditions. Our device does not suffer from high temperature, and spectra do show strong stability, preserving features. These experiments, as well as others in progress, show the I_SMART SiC-based device skills to operate in harsh environments, whereas other materials would strongly suffer from degradation. Work is still demanded to test our device at higher temperatures and to enhance efficiency in order to make our device fully exploitable from an industrial point of view.

4H-SiC P + N UV Photodiodes for Space Applications

Spectral sensitivity measurements versus temperature have been carried out on irradiated SiC p+n photodiodes, fabricated using two different doping processes: Aluminium standard implantation and Boron plasma immersion ion implantation. The spectral sensitivity of Al doped photodiodes increase for incident wavelength higher than 270 nm, and are very stable below. Boron doped irradiated photodiodes show a general increase of the photoresponse for all wavelengths. In both cases, an hysteresis effect is observable when with the temperature. Results are presented and discussed.

Plasma Immersion Ion Implantation Applied To N+P Junction Realisation In 4H‐SiC

This paper focuses on the process giving rise to Nitrogen introduction into SiC p‐type epitaxial layers. Standard ion implantation and PULSION™ processes are performed at two distinct energies (700 eV and 7 keV), followed by an annealing at 1600 °C in a furnace specifically adapted to SiC material, aiming at creating thin n+p junctions. The doping profiles issued from the implantations show an important channeling effect for all samples. Surface roughness and Nitrogen activation after annealing are studied using AFM and Micro‐Four Point Probe means, respectively. A better surface morphology is found on plasma‐implanted samples, with a higher sheet resistance (in comparison with standard samples) which could either be related to a lower implanted dose and/or to a lower dopant activation.