Papers by Author: Christian Brylinski

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: 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: 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: This work reports on the characterization of the decomposition of GaN layers epitaxied on c-plane Sapphire substrate by Differential Scanning Calorimetry. Many configurations have been characterized from two different GaN epilayer providers with a large range of doping concentrations from Non-intentionally Doped layers up to 2x10¹⁹ cm^-3. All intentionally doped layers exhibit an endothermic reaction starting at 200-300 °C while the NiD layer thermogram is the same as the blank experiment. XPS and SEM observations demonstrated that the endothermic reaction is related to the GaN decomposition through Threading Dislocation and nanoPipe.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: Selective epitaxial growth in buried patterns was studied using the vapour-liquid-solid mechanism in Al-Si melt in order to obtain p+-doped SiC localized layers on 4H-SiC substrate. Homogeneous deposition with step bunched morphology was obtained by adding propane at room temperature before growth at 1100°C. Patterns as large as 800 µm and as narrow as 10 µm were completely filled in this way. The deposition kinetics demonstrates that the process is self limited and mainly depends on the initial amount of Si in the liquid. The deposit is highly p-type doped and the p-n junction is demonstrated.

Abstract: The crystal growth of 3C-SiC onto silicon substrate by Vapour-Liquid-Solid (VLS) transport has been investigated. In the studied growth configuration, propane feeds a SiGe liquid phase contained in 10 µm-deep etched trenches on the Si substrate. Before SiGe deposition, the substrate surface and the trench walls were coated with a thin (100 - 200 nm) CVD-grown 3C-SiC seeding layer. For the VLS growth, the temperature was increased up to 1280°C, above the SiGe alloy melting point, at which point propane was added to start VLS growth. X-ray diffraction shows that some SiC is grown epitaxially onto the CVD seeding layer. However, cross-section SEM observations have evidenced that SiC has grown as trapezoidal islands and not as an uniform layer. Backscattered electron images also clearly show a deep penetration of germanium into the substrate through the SiC seeding layer. This penetration was found to be strongly reduced when increasing the seeding layer thickness from 100 to 200 nm.

Abstract: Ohmic contacts represent a major technological brick for the development of high power devices on Gallium Nitride. Al(200 nm) Ti(70 nm) metallization on n+-GaN, annealed at 650 °C, provides a “Specific Contact Resistivity” (SCR) in the range mid 10-5 Ω.cm², which is low enough for the main switching power applications. However, the Al-Ti metallic compound phases formed during the annealing step result from solid-solid reactions, which may lead to high stress and / or poor cohesion, possibly deleterious to contact reliability. In this work, we have investigated several configurations of Ti-Al-Si based contacts, aiming at favoring liquid-solid reactions and / or Si element diffusion, in order to get better SCR and / or morphology and cohesion of the metallic phase. Surprisingly, only contacts annealed at low temperature (450 °C) provide low contact SCR, comparable to that of Ti-Al only contact, but systematically higher.