Abstract: In accordance with the invention, a quantum well device provides localized states for electrons having an energy E greater than the barrier height of the constituent quantum wells. The device comprises a confinement quantum well of width L.sub.w equal to an integer number n of deBroglie half wavelengths ##EQU1## and a plurality of adjacent quarter wavelength barriers and wells, each having a thickness equal to an odd number m of deBroglie quarter wavelengths. Constructive interference between the waves partially reflected by the interfaces between adjacent .lambda./4 barriers and .lambda./4 wells leads to the formation of a localized electron state at an energy E in the region of the confinement well. The device can be used in detectors and modulators employing transitions between a bound state within the well and the localized state above the well.

Abstract: The invention relates to a method of implementation of surface-emission laser diodes with multiple quantum wells, including a single epitaxy step and a single step of implantation and diffusion of doping impurities. The transverse dimensions of the laser are determined by application of a mask on the active region before the implantation of said doping impurities around said active region, thus avoiding the conventional step of chemical etching with its detrimental effects on the expected lifetime of the finished laser. The construction of the laser of the invention allows to optimize separately the characteristics of optical confinement (along the axis of propagation of the laser light) and of confinement of the charge carriers in said active region (perpendicularly to said axis of propagation).