Palladium is chemically suitable for electric contacts on mercuric iodide detectors for photon and nuclear radiation detection, so the understanding of palladium contacts is important for fundamental and practical scientific purposes. A study has been conducted on the surface morphology of evaporated contacts using atomic force microscopy and optical transmission and reflection. Evaporated palladium coatings are typically non-uniform and may deposit selectively on mercuric iodide surface defects. Reflection measurements show that the coating thickness and the surface treatment affect the intensity, position and shape of a reflected peak characteristic of the mercuric iodide structure. The results indicate that the band gap energy in the surface of the mercuric iodide is lowered by palladium contacts.