Charlotte has some duplexes. They are not as common as in areas up North. We don't usually have duplexes selling to home buyers who want the second side as an income stream. In Charlotte duplexes usually only sell to investors. So they do not appreciate as quickly as single family homes. However they are good rentals because if one side is vacant you do have some income from the other side.
You also will want to consider your potential tenants. Who does your home appeal to? Will it be a family home with 4 kids and two dogs, or a single professional who works uptown but parties every night? What will the repairs on the home entail?
I suggest you get an experienced real estate to work with you in your investment property search. If you do not live in Charlotte or are not familiar with the neighborhoods you can save yourself much pain and gain much profit by teaming with a real estate expert.