3C-Silicon Carbide (SiC) as a material of choice for high-performance low-cost power electronic devices

Abstract

The high power density requirements of modern power electronics applications has made Wide Band Gap (WBG) semiconductors to be considered as the next generation electronic material. The supreme electrical and thermal properties of the WBG compounds, such as Silicon Carbide (SiC) and Gallium Nitride (GaN), offer the potential for power devices with the capacity to outperform their Silicon (Si) counterparts. Yet, the shifting from Silicon to WBG technologies is not rapid, but rather occurs gradually. This is mainly due to the higher WBG process cost compared to the conventional Si devices, which still constitutes an established and reliable technology platform.
The focus of this thesis is on the cubic phase of SiC, also referred to as β- or 3C-SiC, and power devices based on this compound. Owing to its cubic symmetry, 3C-SiC can be grown on top of large Si substrates (3C-SiC-on-Si) enabling cost-effective and isotropic WBG performance. These advantageous characteristics, coupled with recent advancements on the bulk 3C-SiC-on-Si material quality, highlight β-SiC as an emerging technology for power devices.
The stepping stone towards investigating the true potential and the boundaries of this emerging SiC technology, comprises the development of an accurate material model for 3C-SiC compatible with Technology Computer Aided Design (TCAD) software tools, which is reported in this thesis and did not exist prior. The material level validation of the 3C-SiC model with measurements enabled device level simulations and the derivation of an advanced defect-based model to justify the excessive leakage current evidenced in SiC Schottky Barrier Diodes (SBDs). The latter TCAD model, essentially links the presence of defects, both bulk and Schottky interface states, with complex trapping/de-trapping phenomena. In addition, the model accommodates for the inhomogeneous electrical behaviour of the Schottky Barrier Height (SBH). Overlapping spatial distributions of modelled trap profles, featuring different energetic distributions, results in a non-uniform spatial distribution of the electric feld on the Schottky active area. Thereafter, a simulation study compares the 3C-SiC with the more mature and commercialized 4H-SiC, in the context of power diodes, both Junction Barrier Schottky (JBS) x | Abstract and P-i-N. Static performance maps, in terms of on-state voltage drop and blocking voltage capabilities, are created and the limits of each technology are identifed.
The Carbon Cluster model allowed for the characterization of the various types of defects at the semiconductor / SiO2 interface. The 3C-SiC benefts from a relatively smaller band gap value to exclude the effect of specifc traps, which majorly degrade the carriers’ mobility within the channel region of Metal Oxide Semiconductor (MOS) structures in other SiC polytypes. An additional model to accurately predict the high channel mobility of electrons demonstrated in 3C-SiC MOS-Field Effect Transistors (FETs) is presented and validated with measurements in this thesis, adding to the bulk mobility model. Nonetheless, 3C-SiC-on-Si MOSFETs are currently implausible following the conventional process for SiC unipolar power switches, due to the limited activation of the acceptor-type dopants with ion-implantation. A novel process for SuperJunction (SJ) JFET MOSFETs is proposed, considering two design splits, both evaluated with simulations. The results indicate that the suggested SJ JFET designs have the potential to deliver viable 3CSiC-on-Si MOSFETs with remarkable electrical performance, disrupting the current material limitations.
Comprehensively, this thesis targets to model and analyze the effects of the traps existing in 3C-SiC-on-Si and, thereafter, investigate the true potential of high performance power diodes and MOSFETs based on the cubic phase of SiC grown on Si, given the recent improvements of the material quality.

Date of Award	2021
Original language	English
Awarding Institution	Coventry University
Supervisor	Neo Lophitis (Supervisor), Marina Antoniou (Supervisor), Konstantinos Gyftakis (Supervisor) & Mike Blundell (Supervisor)