Sublimation bulk growth in vacuum using graphite crucibles and such with tantalum shielding of the crucible walls has been studied. Residual nitrogen, aluminum and boron doping in the material grown in vacuum is presented. Activation energies of growth rate in respect to growth temperature in vacuum are deduced. The estimated values are 21 kcal/mole for growth temperatures below 2075degreesC and 128 kcal/mole in the range of growth temperatures between 2075degreesC and 2275degreesC. Cathodoluminescence spectra taken from samples grown in the graphite crucible in absence of tantalum under different pressures show nitrogen-aluminum DAP transition and strong luminescence from deep boron. This is not the case for samples grown in the tantalum environment.