SEMICONDUCTOR LAYER COMPRISING CYCLICALLY STACKED NARROW, INTERMEDIATE, AND WIDE BAND GAP SEMICONDUCTOR FILMS

摘要

A semiconductor layer which for reflecting anoptical beam comprises a plurality of film pairs of narrowand wide band gap semiconductor films having a refractiveindex difference and narrower and wider band gaps. Anintermediate semiconductor film is interposed between thenarrow and the wide band gap semiconductor films of eachfilm pair and is made to have an intermediate film band gapwhich is varied so as to be equal to the narrower and thewider band gaps at its interfaces contiguous to the narrowand the wide band gap semiconductor films. The narrow bandgap semiconductor film, and a portion adjacent thereto inthe intermediate semiconductor film, are called a firstcomposite layer and are given a first total thickness whichis approximately equal to a quarter of a first wavelengthhad by the optical beam in the first composite layer. Thewide band gap semiconductor film, and a remaining portionadjacent thereto in the intermediate semiconductor film,are called a second composite layer and are given a secondtotal thickness which is approximately equal to a quarterof a second wavelength had by the optical beam in thesecond composite layer. Preferably, the intermediatesemiconductor film should have a film thickness which issubstantially equal to a width which a potential barrierwould have perpendicular to the film pairs if theintermediate semiconductor film were absent. Morepreferably, absorption of the optical beam in the narrowand the wide band gap semiconductor films is taken intoaccount on determining their thicknesses.