What is the alternative for BYW98 diode?
Mall Lawyers would charge $50 for this free service.  Don't abuse it.

STMicroelectronics STTH302  is suitable with &lt;20ns reverse recovery time at voltages from 100 to 600V and wide range of currents like 6A
http://www.digikey.com/product-detail/en/stmicroelectronics/STTH3R02AFY/497-15974-2-ND/5418230

BYW98 diode and many like it are obsolete.

I trust you understand the importance of ultra fast reverse recovery times and improved products avail displacing obsolete parts .