Nicolas Thierry-Jebali

Very low specific contact resistance measurements made on a highly p-type doped 4H-SiC layer selectively grown by vapor-liquid-solid transport

This work reports on the performances of ohmic contacts fabricated on highly p-type doped 4H-SiC epitaxial layer selectively grown by vapor-liquid-solid transport. Due to the very high doping level ...

Observation of the generation of stacking faults and active degradation measurements on off-axis and on-axis 4H-SiC PiN diodes

PiN diodes have been fabricated on nominally on-axis Si-face 4H-SiC material and their electrical characteristics are compared to PiN diodes processed with exactly the same device process recipe on 8°-off 4H-SiC material. Some diodes had an optical window on the top metal contact to observe the possible stacking faults generation and motion with photo emission microscopy. The diodes were electrically characterized in forward voltage to test their stability. Electrical characterizations demonstrate that there is no noticeable degradation for the diodes processed on on-axis 4H-SiC substrate and with optical characterization the formation of stacking faults was not observed.

Electrical Characterization of PiN Diodes with p+ Layer Selectively Grown by VLS Transport

This paper deals with electrical characterization of PiN diodes fabricated on an 8° off-axis 4H-SiC with a p++ localized epitaxial area grown by Vapour-Liquid-Solid (VLS) transport. It provides for the first time evidence that a high quality p-n junction can be achieved by using this technique followed by a High Temperature Annealing (HTA) process.

600 V PIN Diodes Fabricated Using On-Axis 4H Silicon Carbide

This paper reports the fabrication and electrical characterization of PiN diodes on an on-axis grown epitaxial layer. TCAD simulations have been performed in order to design their architecture. Some of these diodes have a breakdown voltage around 600 V. A comparison is made with similar diodes fabricated on off-cut grown layers. Computer simulations are used to explain lower breakdown voltage than those expected.

Applications of Vapor-Liquid-Solid Selective Epitaxy of Highly p-Type Doped 4H-SiC: PiN Diodes with Peripheral Protection and Improvement of Specific Contact Resistance of Ohmic Contacts

This work deals with two applications of the Selective Epitaxial Growth of highly p-type doped buried 4H-SiC in Vapor-Liquid-Solid configuration (SEG-VLS). The first application is the improvement of the Specific Contact Resistance (SCR) of contacts made on such p-type material. As a result of the extremely high doping level, SCR values as low as 1.3x10-6 Ω.cm2 have been demonstrated. Additionally, the high Al concentration of the SEG-VLS 4H-SiC material induces a lowering of the Al acceptor ionization energy down to 40 meV. The second application is the fabrication of PiN diodes with SEG-VLS emitter and guard-rings peripheral protection. Influence of some process parameters and crystal orientation on the forward and reverse characteristics of the PiN diodes is discussed.

Characterization and kinetic monitoring of the reactions between TixAly phases in Ti-Al based ohmic contacts on n-type GaN by Differential Scanning Calorimetry (DSC)

This work reports on DSC measurements performed on Ti-Al metallic layers stacks deposited on n+-GaN. The aim is to get better understanding of the mechanisms leading to ohmic contact formation during the annealing stage. Two exothermic DSC peaks were found : one below 500°C and the other one around 660°C. They can be respectively attributed to Al3Ti and Al2Ti compounds formation. Lowest contact resistance is well correlated with the presence of Al3Ti compound, corresponding to Al(200nm) / Ti(50nm) stoichiometric ratio. Subsequently, Al (200 nm) / Ti(50 nm) stacks on n+-GaN were comparatively annealed from 400 °C to 650 °C. Specific Contact Resistivity (SCR) values stay in the mid 10-5 Ω.cm2 range for annealing temperatures between 450 °C and 650 °C. Such low-temperature annealed contacts on n+-GaN may open new device processing routes, simpler and cheaper, in which Ohmic and Schottky contacts are annealed together.

Study of the Nucleation of p-Doped SiC in Selective Epitaxial Growth Using VLS Transport

This work deals with the study of the Selective Epitaxial Growth (SEG) of SiC using Vapour-Liquid-Solid (VLS) transport at temperature ≤ 1100°C. Focus was made on the nucleation step by observing the evolution of the growth as a function of growth duration with variable Si-content of the Al-Si liquid phase. Addition of propane during the initial heating ramping-up not only avoids liquid de-wetting but also allows good starting of the epitaxial growth. Additionally, it was observed that, by increasing the silicon content in the liquid, the morphology of the grown SiC is improved, and no parasitic Al4C3 inclusions are formed. Limiting the growth rate is found to be essential for getting controlled smooth growth process.

Active Devices for Power Electronics: SiC vs III-N Compounds – The Case of Schottky Rectifiers

The main rectifier device structures for power electronics based on SiC and on GaN are compared and the main issues for each structure are evaluated in terms of performance and manufacturability. The driving volume markets for power electronics devices correspond to the systems working on 127, 240 and 400 V energy supply networks, setting the device voltage handling to 300, 600, and 1200V respectively. We have limited the scope hereafter to the 600 V typical target, for which SiC Schottky rectifiers are now commercially available from at least 3 sources. The key physical properties for any semiconductor material used as the active layer of a unipolar device for power electronics are the breakdown field and carriers mobility. The bulk values are very similar for SiC and GaN. Two main other key issues are related to quality of the ohmic and Schottky contacts. For the ohmic contacts, adequate solutions have been found for both SiC and GaN. Surprisingly, on hetero-epitaxial GaN layers on sapphire despite of the very high crystal defects density ( ≥ 109cm-2 ), the ideality factor of the best Schottky contacts seems very promising. On the other hand, improving this ideality factor and the reverse leakage current for Schottky contacts on GaN layers grown on silicon substrate remains a fierce challenge. For the SiC Schottky rectifiers, cost and availability of the SiC substrates appear as the main residual limiting factors today. For GaN based rectifiers, although engineering device prototypes have already been published [1], there are both basic issues to be validated regarding reverse leakage current and reliability, and also difficult manufacturing issues to be solved in relation with device reliability, directly resulting from the nature of the possible substrates: mainly sapphire and silicon.

Study and Optimization of a 600V Pseudo-Vertical GaN-on-Silicon Rectifier by Finite Element Simulations

This work presents the impact analysis of physical and geometrical parameters on the on-resistance and the breakdown voltage in order to optimize a 600 V pseudo-vertical GaN/Si Schottky rectifier. The results by finite element simulations indicate that the most influent parameter on the resistance is the thickness of the n+ layer. Regarding reverse specifications, simulations show that a good efficiency of the “Mesa + Guard Ring” is achieved for a guard ring doping concentration higher than Na=5×1017 cm-3.

Design optimization of a high temperature 1.2 kV 4H-SiC buried grid JBS rectifier

1.2 kV SiC buried grid junction barrier Schottky (BG-JBS) diodes are demonstrated. The design considerations for high temperature applications are investigated. The design is optimized in terms of doping concentration and thickness of the epilayers, as well as grid size and spacing dimensions, in order to obtain low on-resistance and reasonable leakage current even at high temperatures. The device behavior at temperatures ranging from 25 to 225ºC is analyzed and measured on wafer level. At 100 A/cm2 a forward voltage drop of 2 V at 25ºC and 3 V at 225ºC is achieved. At reverse voltage of 1 kV, a leakage current density below 0.1 µA/cm2 and below 0.1 mA/cm2 is measured at 25 and 225ºC, respectively. This proves the effective shielding effect of the BG-JBS design and provides benefits in high voltage applications, particularly for high temperature operation.