Only a few years ago, an account of degradation of silicon carbide high-voltage p-i-n diodes was presented at the European Conference on Silicon Carbide and Related Compounds (Kloster Banz, Germany, 2000). This report was followed by the intense effort of multiple groups utilizing varied approaches and subsequent progress in both fundamental understanding of this phenomenon and its elimination. The degradation of SiC p-i-n junctions is now well documented to be due to the expansion of Shockley-type stacking faults in the part of the devices reached by the electron-hole plasma. The faults can gradually cover most of the junction area, impeding current flow and, as a result, increasing the on-state resistance. While in most semiconductors stacking faults are electrically inactive, in hexagonal silicon carbide polytypes (4H- and 6H-SiC) they form quantum-well-like electron states observed in luminescence and confirmed by first-principles calculations. The stacking-fault expansion occurs via motion of 30° sil...

Degradation of hexagonal silicon-carbide-based bipolar devices

Conductive polypyrrole/SiC nanocomposites are fabricated via a facile oxidative polymerization approach using p-toluene sulfonic acid as a dopant and ammonium persulfate as an oxidant. The effects of the nanoparticle loading, ratio of oxidant to monomers, and nanoparticle morphology (spheres and rods) on the physicochemical properties are investigated. Various characterization methods are carried out to determine the material properties. Thermal gravimetric analysis demonstrates an improved thermal stability of polypyrrole in the polymer nanocomposites (PNCs) with a higher decomposition temperature. The glass-transition temperature and melting temperature of the polymer and its nanocomposites are determined by differential scanning calorimetry with a decreased melting temperature of polypyrrole in the PNCs. The microstructures of pure polypyrrole and PNCs are observed by scanning electron microscopy. Powder X-ray diffraction analysis demonstrates the crytallinity of polypyrrole, and poor crystallinity is ...

Polypyrrole/Silicon Carbide Nanocomposites with Tunable Electrical Conductivity

The search for materials and systems, capable of operating long term under physiological conditions, has been a strategy for many research groups during the past years. Silicon carbide (SiC) is a material, which can meet the demands due to its high biocompatibility, high inertness to biological tissues and to aggressive environment, and the possibility to make all types of electronic devices.This paper reviews progress in biomedical and biosensor related research on SiC. For example, less biofouling and platelet aggregation when exposed to blood is taken advantage of in a variety of medical implantable materials while the robust semiconducting properties can be explored in surface functionalized bioelectronic devices.

https://iopscience.iop.org/article/10.1088/0022-3727/40/20/S20/pdf

Surface functionalization and biomedical applications based on SiC

A previously unreported photoluminescence spectrum observed in certain 4H SiC bipolar diodes after extended forward voltage operation is reported. We assign this emission to exciton recombination at local potential fluctuations caused by stacking faults, which are created during operation of the diodes. Possible recombination mechanisms responsible for the spectrum are discussed.

Luminescence from stacking faults in 4H SiC

https://www.ctcms.nist.gov/%7Edavydov/12Williams_SiC%20bio-functionalization_ApplSS_258.pdf

Immobilization of streptavidin on 4H-SiC for biosensor development

Silicon Carbide device technology is now evolving from a pure vision to a real alternative to silicon devices. The feasibility of SiC devices has been shown for many different types of devices, the development of a working production technology has started, yield, reliability and costs now being the key issues. At present the high substrate prices keep the manufacturing costs of SiC high, making it very difficult to enter the device market with SiC on economic terms. Prime applications are those for which SiC offers substantial benefits or even a technological breakthrough on the system level. The main application is power conversion where the latest development efforts on silicon based power switches (e.g. IGBT) allow utilisation of much higher switching frequencies, putting very high demands on the free wheeling diode. The system performance is to a large extent limited by the diode recovery charge—a major source of switching losses. Depending on the voltage range, different device concepts are of interest: In the lower voltage range the junction–barrier controlled Schottky (JBS) device is a promising candidate while at voltages beyond 2.5 kV the PIN diodes is the device of choice. Different system requirements—e.g. surge current capability—make the PIN junction superior to a Schottky device for certain applications. With progress in material and technology development the ‘world’s best’ result is becoming less and less important and reproducibility is the issue. Failure analysis of defective devices needs to be established with a high number of substrate defects being still an obstacle in SiC. High leakage/soft reverse characteristics are often encountered and can usually be attributed to localised defects. It is important to identify their origin and to separate process-induced defects from those already present in the epilayer or substrate. In order to use the high power handling capability of SiC reduction of margins (e.g. in epilayer thickness and doping) is necessary. This requires narrow bandwidth of process and material variations. For paralleling of SiC devices equal current sharing under static and dynamic conditions is a fundamental requirement from the system side. Top-down calculation gives material specifications, which the supplier has to meet.

D Mou

Papers

SiC power devices for high voltage applications