In this paper, a double implanted vertical npvn 4H-SiC power bipolar transistor (BJT) is studied using TCAD simulation. The choice of physical models employed in the simulations is shown to markedly affect critical device characteristics such as current gain. Incomplete ionisation of accepters in the base region is shown to result in dramatically increased gain at room temperature but a reduced current drive capability, which is caused by emitter current crowding. The effects of band-gap narrowing and lifetime variations are also studied. The simulations demonstrate that a SiC power BJT should indeed be a viable device but that much work needs to be done to improve the accuracy of physical models, and for implanted SiC in particular, before reliable predictions can be made.