Cubic silicon carbide grown by thermal decomposition of methyl trichlorosilane in hydrogen has been studied in infrared (IR) transmission, cyclotron resonance (CR), and photoluminescence (PL). Sample characteristics include: The nitrogen concentration, determined from CR and IR can be of the order of 1015 cm-3 or less. Ionized impurity concentrations determined from the linewidths of CR and IR spectra can be less than 7 × 1014 cm-3. Low temperature electron mobilities from CR are near 105 cm2 v-1 s-1. Carrier freeze-out is consistent with either uncompen-sated donors with activation energy near 50 meV or heavily compensated donors with 20 meV activation energy. The latter choice, however, is excluded by the low ionized impurity concentration. These high quality samples show little or no evidence of the apparently shallow (< ∼20 meV) donor which usually dominates the low temperature conductivity of 3C-SiC grown on Si. Nitrogen donor excitation spectra are in excellent agreement with effective mass theory. Only nitrogen donors at 54.2 meV and an unidentified effective-mass donor at 47.8 meV are observed. If material with the characteristics described above can be reliably reproduced then there is substantial expectation that high quality electronic devices based on 3C-SiC can be fabricated.