Effect of boron diffusion on the high-voltage behavior of 6H-SiC p+nn+ structures

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Abstract
Boron diffusion can be used to compensate the n‐type layer of a p+nn+ 6H‐silicon carbide structure in order to increase its high‐voltage capabilities. Measurements under reverse biases for a current range from 10 to 500 μA show that this process is very efficient for working temperatures about 300 K. Indeed we obtained a voltage of 670 V for a reverse current of 10 μA instead of the 120 V calculated for a structure without boron diffusion. Nevertheless, the breakdown voltage decreases rapidly when the temperature increases. Capacitance measurements show that the measured doping level in the n‐type layer evolves in the same way as the temperature (it ranges from 1013 cm−3 at 300 K to 1017 cm−3 at 500 K). A great concentration of boron seems to be responsible for this doping variation with temperature. Admittance spectroscopy reveals the presence of D centers at 0.62 eV above the valence band associated to boron at concentration similar or superior to nitrogen concentration in the n‐type layer. The increase of the doping level with the temperature is responsible for this decrease of the breakdown voltage.

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