Abstract: A photo coupler comprises a multilayer insulating substrate having a cavity on a predetermined portion and a first conductive layer at the bottom of the cavity and a second conductive layer on one surface of the insulating substrate. A light emitting diode is disposed in the cavity with a substantial light emitting zone thereof being in the cavity and is electrically connected to the first conductive layer. A photo responsive device is placed above the cavity on the substrate with the photo sensitive surface of the device facing the light emitting diode and being electrically connected to the second conductive layer.

Abstract: A recess is formed in one of the principal surfaces of an N-type substrate of GaAs. Through the liquid phase growth technique, a silicon-doped N-type GaAs layer is formed on the one of the principal surfaces and on the surface of the recess and a silicon-doped P-type GaAs layer is continuously formed on the N-type GaAs layer. The liquid-phase-grown GaAs layers are so cut that the PN junction between the layers may be exposed on a plane.