Distribution of the electrical resistivity of a n-type 4H-SiC crystal

Abstract

Nitrogen is commonly doped to obtain n-type 4H-SiC crystals, which have been commercialized for the development of power electronics in recent years. Now the uniformity of electrical resistivity becomes an important issue for the growth of n-type 4H-SiC crystals. In this work, the effects of the radial thermal gradient and growth facet on the distribution of the electrical resistivity were investigated for a n-type 4H-SiC crystal with a diameter of 150 mm during its physical-vapor-transport growth. It is found that the resistivity at the center of the crystal is low in the early growth stage. As the crystal grows, the growth facet expands, accompanied by a reduction in the resistivity of this facet. The change in the distribution of the resistivity in the crystal is initially governed by the radial thermal gradient and then influenced by the spiral growth mode of the growth facet. In the non-facet region of the crystal step-flow growth occurs, where the doping of nitrogen is primarily affected by the temperature and C/Si ratio. In the facet region, the volume fraction of nitrogen in the mixture of argon and nitrogen input into the growth system mainly governs the doping of nitrogen during the spiral growth. The insights gained in the current work may help the fabrication of n-type 4H-SiC crystals with uniform resistivity.