The module shown here is a 1200V 300A single switch/FWD (free wheeling diode). This manufacturer rates the FWD with the same rating as the IGBT, i.e. the FWD in this module is rated at 300A.  If the module contained a SiC Schottky FWD, its rating should be approximately 150A. The rating can be less with SiC because of the elimination of reverse recovery currents. Forward voltage drop will be the main parameter of interest with SiC parts. The higher the rating of the SiC diode the lower the forward voltage drop and thereby the higher the system efficiency. Therefore, efficiency can be added by increasing the diode size. It is basically a price/performance decision.