How to set Identity on Var char column?

Hi, I need to create a table with identity column, but the identity should be in string format. But In my table the column datatype is var char.

I need to increment to my column values like      100.1.01

                   100.1.02

           100.1.03 .......etc

How can i do this using Transact SQL

Regards,

Siva.