Elemental semiconductor mirror for vehicles and method for making same

Abstract

A elemental mirror for vehicles having a luminous reflectance of at least about 30% includes a substrate coated with a thin layer of elemental semiconductor having an index of refraction of at least 3 and an optical thickness of at least about 275 angstroms. Preferably, the elemental semiconductor coating is sputter coated silicon or germanium and a light absorbing coating is included therebehind. The mirror is spectrally nonselective with elemental semiconductor optical thicknesses of about 275 to 2400 angstroms on the front substrate surface. Spectrally selective mirrors are provided by adding an interference coating to the elemental semiconductor layer coating, preferably of a dielectric such as silicon dioxide or silicon nitride, on either the front or rear substrate surface, or by using a thicker, single elemental semiconductor layer. Instead of an absorbing coating behind the mirror, additional elemental semiconductor and dielectric thin layers may be included to reduce secondary reflections. The method includes coating the thin elemental semiconductor layer on flat glass and heating to harden the layer and make it more scratch resistant, or heating and bending the glass without destroying the reflective properties of the mirror. The thin interference layer, secondary reflection reducing layers, and/or light absorbing coating may be coated before or after heating and bending.