Modelling of effective minority carrier lifetime in 4H-SiC n-type epilayers

We present an extended model for the simulation of the effective minority carrier lifetime in 4H-SiC epiwafers after optical excitation. This multilayer model uses measured values (doping profile, point defect concentration, capture cross sections for electrons and epilayer thickness) as input parameters. The bulk lifetime and the diffusion constant are calculated from the actual time dependent excess carrier profiles, resulting in more realistic transients having different decay regimes than in other models. This enables a better understanding of optical lifetime measurements

Improvement of 4H-SiC material quality: Invited paper presented at the First International Symposium on SiC Spintronics, Vadstena, Sweden, June 15-17, 2015

The Fraunhofer IISB will introduce its activities in Silicon Carbide to the spintronic community with a special focus on its undertakings on material development and characterization. Our activities in materials development started about 10 years ago. We were improving the 4H-SiC homoepitaxial growth process in order to avoid extended defects, e.g. dislocations and stacking faults, in homoepitaxial layers. We were able to avoid device-killing defects like Basal Plane Dislocations in epilayers and explained these experimental results by appropriate models. Within the last years, the improvement of the minority carrier lifetime by reducing the point defect density has come into focus. Therefore, the influence of epigrowth parameters like, e.g. gas mixing and growth temperature, on the point defect density and carrier lifetime are investigated by using Deep Level Transient Spectroscopy (DLTS) and microwave-detected photoconductivity decay (µ-PCD). Our recent developments target on the reduction of the carbon vacancy, which is known as a lifetime-killing defect. The experimental work is completed by implementing models regarding the point defect generation / annihilation as well as the carrier lifetime measurements. Besides the materials development, the Fraunhofer IISB has been manufacturing SiC electronic devices for more than 20 years. We are producing power electronic as well as optoelectronic SiC devices in small series or prototype fabrication. The process line could be used also to fabricate spintronic prototype devices. In our presentation, we will show and discuss ou r recent advances in materials development and characterization as well as introduce the device processing

Modelling of effective minority carrier lifetimes in 4H-SiC n-type epilayers: Poster presented at International Conference on Silicon Carbide and Related Materials, ICSCRM 2015, Giardini Naxos, Italy, October, 4th - 9th, 2015

We present an extended model for the simulation of the effective minority carrier lifetime in 4H-SiC epiwafers after optical excitation. This multilayer model uses measured values (doping profile, point defect concentration, capture cross sections for electrons and epilayer thickness) as input parameters. The bulk lifetime and the diffusion constant are calculated from the actual time dependent excess carrier profiles, resulting in more realistic transients having different decay regimes than in other models. This enables a better understanding of optical lifetime measurements

Influence and mutual interaction of process parameters on the Z1/2 defect concentration during epitaxy of 4H-SiC

The development of bipolar 4H-SiC devices for high blocking voltages requires the growth of high carrier lifetime epitaxial layers with low Z1/2 concentrations. This paper shows a comprehensive investigation of the influence of epitaxial growth parameters (C/Si ratio and growth temperature) on Z1/2 concentration and minority carrier lifetime. On the basis of a discovered exponential correlation of Z1/2 with the C/Si ratio and growth temperature, a competitive low Z1/2 concentration of 1.9∙1012 cm-3 could be achieved by lowering the growth temperature and switching to higher C/Si ratio. Thermodynamic considerations by an Arrhenius approach reveal a dependency of the formation enthalpy of Z1/2 on the thermal process and process conditions of the epitaxial growth. Furthermore, the correlation between Z1/2 and the effective minority carrier lifetime confirms the occurrence of a necessary second recombination mechanism beside the common recombination at deep levels by Shockley-Read-Hall for low Z1/2 concentration