Papers by Author: Christophe Raynaud

Abstract: Schottky barrier height (SBH) has been characterized on 4H-SiC Schottky diodes with metal contact of Ti/W by Current-Voltage (I-V) and Capacitance-Voltage (C-V) measurements between 80 K and 400 K. Multi-barrier has been recognized and calculated according to different models. No clear difference has been found between single barrier diode and diode with multi-barrier from DLTS tests. Evolution on the I-V characteristics has been observed after high temperature annealing. The effect of annealing at room temperature (RT) and high temperature DLTS scan (stress under high temperature) have also been studied on both static characteristics and DLTS results.

Abstract: This paper presents OBIC measurements performed at near breakdown voltage on two devices with different JTE doses. Overcurrent has been measured either at the JTE periphery or at the P⁺ border. Such overcurrent is present due to the electric field enhancement near the breakdown voltage. This hypothesis is proved by the electroluminescence. TCAD simulation of two different JTE doses yielded similar results to the OBIC measurements.

Abstract: Carbon materials are considered building blocks for most of electrochemical sensors. Their biocompatibility allows their use as transducers for biosensors. Furthermore, they can be patterned, giving interest in all-inclusive bioelectrochemical detection devices. In particular, graphene, boron doped diamond, and pyrolyzed photoresist films are suitable for this kind of application, which would give the ability to use these working electrodes within a fully designed apparatus completed by counter and reference electrode. In this paper, a pioneer work is exposed on the synthesis of these materials for use as electrochemical sensors and as transducers for biodetection of acetylcholine by adsorption of acetylthiocholinesterase. The lowest limit of detection reaches 6.98 μM, sensitivity 5.91 μA/mM, and a linear range from 6.98 μM to 0.55 mM.

Abstract: This study deals with the electrical characterization of PiN diodes fabricated on a 4°off-axis 4H-SiC n⁺ substrate with a n^- epilayer (1×10¹⁶ cm^-3 / 10 µm). Optimized p⁺⁺ epitaxial areas were grown by Vapour-Liquid-Solid (VLS) transport to form p⁺ emitters localized in etched wells with 1 µm depth. Incorporated Al level in the VLS p⁺⁺ zones was checked by SIMS (Secondary Ion Mass Spectroscopy), and the doping level was found in the range of 1-3×10²⁰ at.cm^-3. Electrical characterizations were performed on these PiN diodes, with 800 nm deposit of aluminium as ohmic contact on p-type SiC. Electrical measurements show a bipolar behaviour, and very high sustainable forward current densities ≥ 3 kA.cm^-2, preserving a low leakage current density in reverse bias. These measurements were obtained on structures without any passivation and no edge termination.

Abstract: In this study, the electrical properties of Ti₃SiC₂ based ohmic contacts formed on p-type 4H-SiC(0001) 4°-off substrates were studied. The Ti₃SiC₂ thin films were grown by thermal annealing (from 900°C to 1200°C) of Ti₅₀Al₅₀ layer deposited by magnetron sputtering. XRD analyzes were performed on the samples to further investigate the compounds formed after annealing. Using TLM structures, the Specific Contact Resistance (SCR) at room temperature of all contacts was measured. The temperature dependence (up to 600°C) of the SCR was studied to understand the current mechanisms at the interface and to determine the barrier height value by fitting the experimental results using the thermionic field emission theory. Aging tests showed that Ti₃SiC₂ based contacts were stable up to 200h at 600°C under Ar.

Abstract: P/N junctions have been fabricated with N⁺ commercial 4H-SiC substrate on which Vapor-Liquid-Solid (VLS) selective epitaxy was used to create a localized p-type doping. The influence of the carrier gas nature (argon or hydrogen) has been investigated in terms of quality of the growth morphology, deposit thickness and electrical behavior of the P/N junction. Distinct results have been observed with a clear improvement when using VLS selective epitaxy under hydrogen.

Abstract: Optical Beam Induced Current (OBIC) measurements are performed on 4H-SiC avalanche diodes with a very thin and a highly doped active region. A pulsed green laser, with a wavelength of 532 nm, illuminates a reverse biased diode leading to generate electron-hole pairs in the space charge region. Comparison between the 4H-SiC bandgap and the incident photon energy shows that single photon absorption process can be neglected and two-photon absorption process dominates in this case. Ionization rates are then extracted from multiplication curve in a high electric field range (3 to 5 MV.cm^–1). Results are in good agreement with previous ones obtained on the same diodes using single photon absorption process.

Abstract: The behavior of 4H-SiC power devices in severe environment with varying temperature is a key characteristic indicating their reliability. This paper shows the dependence of the ionization rates of 4H-SiC with respect to temperature. Optical Beam Induced Current (OBIC) measurements have been performed on PN junctions to determine the multiplication coefficient for temperature varying between 100 and 450K. That allows extracting the ionization rates by fitting the curves of multiplication coefficient.

Abstract: Lateral JFET transistors have been fabricated with N and P-type channels tentatively integrated monolithically on the same SiC wafer. Buried P⁺ SiC layers grown by Vapor-Liquid-Solid (VLS) selective epitaxy were utilized as source and drain for the P-JFET and as gate for the N-JFET. The ohmicity of the contacts, both on VLS grown P⁺ and ion implanted N⁺ layers, has been confirmed by Transfer Length Method (TLM) measurements. A premature leakage current is observed on the P/N junction created directly by the P⁺ VLS gate layer, probably due to imperfect VLS (P⁺) / CVD (N⁺) SiC interface.

Abstract: Silicon Carbide (SiC) Junction-Field Effect Transistors (JFETs) are attractive devices for power electronics. Their high temperature capability should allow them to operate with a reduced cooling system. However, experiments described in this paper conclude to the existence of runaway conditions in which these transistors will reach destructive temperatures.