No need for additional indexes here, the where clause is on the clustered index key. You would consider creating indexes when your queries filter or join on other columns
This may be worth reading http://www.sqlservercentral.com/articles/Indexing/68636/
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability