Abstract: Solar cells are fabricated by spraying a dopant coating onto a semiconductor wafer and heating the surface of the wafer using unipolar microwaves. The resultant controlled heating drives dopant atoms from the coating into the wafer to produce a shallow junction at a selectable depth. Advantageously, metallic conductors are predeposited atop the dopant coating and then sintered to the semiconductor by the same unipolar microwave field concurrently with dopant drive-in. Efficient solar cells can be made with this process using polycrystalline silicon, since with unipolar microwave surface heating the grain boundaries do not become so deeply doped as to short circuit the junctions formed in the individual grains. Unipolar microwave heating also may be used to anneal ion implanted semiconductor devices.