At this time, if the film thickness of each layer is made so thick as the wavelength of the de Broglie wave or is made equal to or less than a "critical film thickness", its lattice constant can be brought close to that of the substrate by applying compressive stress to each of the layers without causing any crystal defect. この時に、各層の膜厚を電子のド・ブロイ波の波長程度、あるいは「臨界膜厚」以下とすれば、結晶欠陥を発生させることなく各層に圧縮応力を印加してその格子定数を基板のそれに近づけることができる。 - 特許庁