Minority carrier lifetime measurements on SiC

In recent years the quality of SiC materials has improved profoundly and hence SiC is becoming more and more a competitor to Si for e.g. high-power devices. Since it is a wide-bandgap semiconductor, SiC has a number of advantages when compared to Si. The minority carrier lifetime is one of the fundamental parameters with regard to the performance of semiconductor devices, especially for the application of SiC in high voltage devices. Hence, it is necessary to perform lifetime engineering to gain the best performance of a certain device. In order to manufacture SiC devices with maximum yield, a material characterization with a high resolution is needed, together with a method to investigate the origin of defects in SiC to further improve the quality.

The two contactless and destruction free methods microwave detected photoconductivity (MDP) and photo induced current transient spectroscopy (MD-PICTS) are ideal methods for material quality and defect characterization.

The MDPmap combined with a UV-laser (355 nm) is the ideal tool for the spatial investigation of inhomogeneities in the minority carrier lifetime of SiC with a lower limit of 20 ns.

MD-PICTS measurements enable the temperature dependent investigation of the photoconductivity transient allowing the determination of the defect activation energy and capture cross sections. With the MD-PICTS system it is possible to measure down to 85 K with a liquid nitrogen bath cryostat or even down to 4 K with a helium cooling system. The upper temperature limit is 800 K and hence also deep trap levels can be investigated. With the additional mapping option small samples (2 x 2 cm) can be mapped at different temperatures.

Results

Figure 1 and 2 show a minority carrier lifetime map and a photoconductivity transient of a 4H-SiC sample. Both was measured with the MDPmap with a resolution of 100 µm and a 355 nm laser.

Figure 3 demonstrates a MD-PICTS spectrum with two detected defect levels with activation energies of 0.12 eV and 0.22 eV. The measurement was conducted with an MDpicts and a liquid nitrogen bath.