Current not flowing across boundaries

I'm new to COMSOL and having some trouble getting current to flow across material boundaries in my model using the Joule Heating physics.

I have a semiconductor wire with metal contacts on each end and set a potential on one side and a ground on the other. I created 3 rectangles side by side in one plane geometry and then assigned different materials to each. There is also a form union node at the end of the geometry node.

There is no temperature change from the Joule heating. Everything is in equilibrium with the ambient.

Looking at the current density, I only see variation in the metal contact attached to the potential. There is no current flowing into the semiconductor wire or the grounded metal contact.

Does anyone know what the problem could be?

Thanks