The invention relates to substrates of semi-insulating
silicon carbide used for
semiconductor devices and a method for making the same. The substrates have a resistivity above 106
Ohm-cm, and preferably above 108
Ohm-cm, and most preferably above 109
Ohm-cm, and a
capacitance below 5 pF / mm2 and preferably below 1 pF / mm2. The electrical properties of the substrates are controlled by a small amount of added
deep level impurity, large enough in concentration to dominate the electrical behavior, but small enough to avoid structural defects. The substrates have concentrations of unintentional background impurities, including shallow donors and acceptors, purposely reduced to below 5·1016 cm−3, and preferably to below 1·1016 cm−3, and the concentration of
deep level impurity is higher, and preferably at least two times higher, than the difference between the concentrations of shallow acceptors and shallow donors. The
deep level impurity comprises one of selected metals from the periodic groups IB, IIB, IIIB, IVB, VB, VIB, VIIB and VIIIB.
Vanadium is a preferred deep level element. In addition to controlling the resistivity and
capacitance, a further
advantage of the invention is an increase in electrical uniformity over the entire
crystal and reduction in the density of
crystal defects.