Surface recombination velocities for 4H-SiC: Temperature dependence and difference in conductivity type at several crystal faces

In bipolar SiC devices, which are promising under ultra-high voltage operation, the carrier lifetime is a highly influential parameter for the device performance. Surface recombination is one of the limiting factors for the carrier lifetime, and quantitative values of the surface recombination velocities are required for the design and development of fabrication processes of the devices. In this study, we observe carrier recombination at various temperatures for the Si- and C-faces of n- and p-type 4H-SiC samples and the a- and m-faces of n-type 4H-SiC samples with a treatment of chemical mechanical polishing or reactive ion etching by using the microwave photoconductivity decay method. From the experimental results, we estimate surface recombination velocities and bulk carrier lifetimes of the samples by using an analytical model. As a result, we found the smallest surface recombination velocity of 150 cm/s for the chemical mechanical polished surface of the Si-face of the n-type samples at room temperature. Surface recombination velocities increased with temperature for the chemical mechanical polished surfaces. The surfaces treated with reactive ion etching showed relatively large surface recombination velocities with weak temperature dependence. Based on these results, we discuss the origins of the recombination centers at surfaces of 4H-SiC.