Romain Delamare

Current crowding effects in superconducting corner-shaped Al microstrips

The superconducting critical current of corner-shaped Al superconducting microstrips has been investigated. We demonstrate that the sharp turns lead to asymmetric vortex dynamics, allowing for easier penetration from the inner concave angle than from the outer convex angle. This effect is evidenced by a rectification of the voltage signal otherwise absent in straight superconducting strips. At low magnetic fields, an enhancement of the critical current with increasing magnetic field is observed for a particular combination of field and current polarity, confirming a theoretically predicted competing interplay of superconducting screening currents and applied currents at the inner side of the turn.

High-efficiency solar cell embedded in SOI substrate for ULP autonomous circuits

A low-cost and high-efficiency monocristalline silicon solar cell embedded in a CMOS circuit is proposed for ULP autonomous circuits. Based on a SOI wafer, a photovoltaic lateral diode is realized in the substrate using the fabrication steps of the FD SOI CMOS process of the superposed active circuitry. In case of front side illumination, we achieve 15% efficiency when no CMOS circuit is present, and 11% with an integrated structure in the silicon thin-film overlayer. An efficiency of 19.5% can be further reached in this last case when a 20V bias difference is applied between the thin-film layer and the back contact to deplete the buried oxide / Si substrate interface.

Method for fabricating third generation photovoltaic cells based on Si quantum dots using ion implantation into SiO2

In this paper, we report on the synthesis of silicon quantum dots for photovoltaic applications by means of ion implantation followed by annealing. Nucleation was achieved by implanting Si+ ions into SiO2 thin films, previously thermally grown on a Si(100) substrate, and annealing to 1100 °C. Passivation was used for photoluminescence (PL) measurements. The thickness of the oxide layer, the stoichiometry of the implanted layer, and the depth profiles of the implanted ions were determined for all samples by both Rutherford backscattering spectroscopy (RBS) and ellipsometry techniques. Characterization by transmission electron microscopy (TEM) indicates that the diameter of the silicon quantum dots (Si-QDs) varies from 2 to 4 nm, which is less than the Bohr radius of bulk crystalline Si(∼5 nm). Optical and electrical properties have been investigated by PL and I-V measurements. When passivated silicon nanocrystals (Si-nc) embedded into SiO2 are excited using a 450 nm diode laser, they exhibit a strong PL emission in the range of 650-1000 nm. Based on these investigations, p-type Si-QDs/n-type c-Si junctions were fabricated and electrically characterized in the dark as well as under an AM1.5G terrestrial solar spectrum for nonimplanted, as-implanted, and implanted-annealed samples for different implantation fluences. The electrical curves of the structures under illumination demonstrate the photovoltaic behavior of the Si-QDs. Despite the weak light conversion of these devices, these results remain very promising and offer potentially unprecedented, vast improvements to third generation solar cells.

Room temperature atomic layer deposition of Al2O3 and replication of butterfly wings for photovoltaic application

In this paper, we present two key process steps for potential applications in the fabrication of low-cost and high-efficiency ultrathin monocrystalline silicon (mono-Si) solar cells to effectively harvest solar energy. One is to grow an Al2O3 passivation layer on the rear side of an Si wafer by a successive atomic layer deposition (ALD) at room temperature (25 °C). The other is to produce a bio-inspired antireflection structure on the front side of the Si wafer by replicating butterfly wing patterns. The capacitance–voltage measurements reveal that the successive ALD procedure can yield a higher negative charge density at the Al2O3/Si interface relative to the conventional one. The measurement results of quasi-steady-state photoconductance indicate that after annealing, the 25 °C ALD Al2O3 layers reach a similar passivation level to the p-type Si wafers compared to that deposited at 250 °C. With the help of an ALD Al2O3 layer, butterfly wing patterns (Hypochrysops polycletus) are replicated on a PMMA layer which is on an SiO2/Si stack. This work demonstrates the ability for replicating the natural photonic features on Si wafers and other substrates by using nanoimprint.

Hadrontherapy beam monitoring: Towards a new generation of ultra-thin p-type silicon strip detectors

Hadrontherapy has gained increasing interest for cancer treatment especially within the last decade. System commissioning and quality assurance procedures impose to monitor the particle beam using 2D dose measurements. Nowadays, several monitoring systems exist for hadrontherapy but all show a relatively high influence on the beam properties: indeed, most devices consist of several layers of materials that degrade the beam through scattering and energy losses. For precise treatment purposes, ultra-thin silicon strip detectors are investigated in order to reduce this beam scattering. We assess the beam size increase provoked by the Multiple Coulomb Scattering when passing through Si, to derive a target thickness. Monte-Carlo based simulations show a characteristic scattering opening angle lower than 1mrad for thicknesses below 20 μm. We then evaluated the fabrication process feasibility. We successfully thinned down silicon wafers to thicknesses lower than 10 μm over areas of several cm2. Strip detectors are presently being processed and they will tentatively be thinned down to 20 μm. Moreover, two-dimensional TCAD simulations were carried out to investigate the beam detector performances on p-type Si substrates. Additionally, thick and thin substrates have been compared thanks to electrical simulations. Reducing the pitch between the strips increases breakdown voltage, whereas leakage current is quite insensitive to strips geometrical configuration. The samples are to be characterized as soon as possible in one of the IBA hadrontherapy facilities. For hadrontherapy, this would represent a considerable step forward in terms of treatment precision.

Technology development on P-type silicon strip detectors for proton beam dosimetry

In this paper, we present a technology for the fabrication of n-in-p silicon strip detectors, which is based on the use of Al2O3 oxide compared to p-spray insulation scheme. This technology has been developed using the best technological parameters deduced from simulations, particularly for the p-spray implantation parameters. Different wafers were processed towards the fabrication of the radiation detectors with p-spray insulation and Al2O3. The evaluation of the prototype detectors has been carried out by performing the electrical characterization of the devices through the measurement of current-voltage and capacitance-voltage characteristics, as well as the measurement of detection response under radiation. The results of electrical measurements indicate that detectors fabricated with Al2O3 exhibit a dark current several times lower than p-spray detectors and show an excellent electrical insulation between strips with a higher inter-strip resistance. Response of Al2O3 strip detector under radiation has been found better. The resulting improved output signal dynamic range finally makes the use of Al2O3 more attractive.