That's an interesting question, Barbara. I'll have to check my annotated Sherlock Holmes while I'm at work later today, to see if any explanation for Doyle's choice of name might be given in there. I also have a friend who's a member of the Sherlockian society "The Baker Street Irregulars", and I'll ask him, as well.
I can tell you that the name "Sherlock" is a genuine surname, having started out as a nickname in England for a person with fair hair or a lock of fair hair. The name is derived from the Middle English word "schirloc", which in turn is derived from the Old English "scir" (meaning "bright" or "fair") and "loc" (meaning "lock of hair").