What is the best material used for full tang or battle ready katanas (samurai swords)?

I'm interested in buying a katana (samurai sword) for actual use. It's just in case of a zombie invasion end of the world scenario. I need it to be sturdy, dependable, not chip or break if it hits anything, and able to slice through the thickest zombie's neck or skull without becoming stuck in said zombie. How should I pick one and what material should it be made of? Could you suggest a website?