Semiconductor structures having a first layer including an n-type III-V semiconductor material and a second layer including an M(InP)(InGaAs) alloy, wherein M is selected from Ni, Pt, Pd, Co, Ti, Zr, Y, Mo, Ru, Ir, Sb, In, Dy, Tb, Er, Yb, and Te, and combinations thereof, are disclosed. The semiconductor structures have a substantially planar interface between the first and second layers. Methods of fabricating semiconductor structures, and methods of reducing interface roughness and / or sheet resistance of a contact are also disclosed.