The resistance to current flow and movement of electron and hole carries in the silicon carbide. Resistivity is related to the ratio of voltage across the silicon to the current flowing through the silicon carbide per unit volume of silicon carbide. The units for resistivity are Ohm-cm, and these are the units used to specify the resistivity of silicon carbide wafers and crystals. Resistivity is controlled by adding impurities such as,Nitrogen or Boron to the silicon carbide. As the amount of impurity or dopant is increased, the resistivity is decreased. Heavy doped material has low resistivity.