As this other article shows, there are four work products in the UX design process for a software product: the Information Architecture (flowcharts), the Interactive Design (wireframes), the graphical composition (comps) and the assets (icons, favicons and more).
In small teams one or two people often cover all these roles. As the team grows and scales, most of the time the roles start to separate and specialize for cross-functional efficiency and effectiveness. A common separation is that the UX designer is in charge of everything up to the interactive design, and then the graphical design is done by a visual designer. However your mileage may vary - there are many highly talented designers who can go end to end.