Your requirement is not clear.
What do you mean by "auto generate"? Are you looking for some kind of an identity column in a custom format?
To ensure you only have unique entries ou could add a UNIQUE constraint to your table. See BOL (BooksOnLine, the SQL Server help system usually installed together with SQL Server), section "ALTER TABLE (Transact-SQL) ".
Please send me t-sql code.
Sure. Please send me the money. 😉
We're here to help you to improve your T-SQL skills, not to do your job for you.
Give it a try first, see where you get stuck and post back what you have so far.