Single-mode, distributed feedback interband cascade lasers

A method of forming an interband cascade layer comprising:

• epitaxially growing an ICL wafer atop a substrate, the ICL wafer comprising at least an active region of semiconductor quantum well structures and at least one confinement layer disposed atop and below the active region, and further comprising at least an upper cladding layer disposed atop the top confinement layer;
• lithographically patterning and etching an elongated waveguide ridge having characteristic width and length dimensions, the longitudinal dimension of the waveguide ridge defining a laser cavity configured to employ intersubband electronic transitions through the upper cladding layer such that the elongated waveguide ridge is disposed atop the top confinement layer;
• epitaxially growing a further cladding layer atop the waveguide ridge;
• lithographically patterning a distributed feedback grating comprising a plurality of vertical corrugations extending outward from the longitudinal edges of the waveguide ridge in a plurality of laterally extending parallel rows;
• plasma etching the patterned plurality of vertical corrugations into the ICL wafer such that the corrugations have characteristic modulation depth and pitch, and such that the corrugations are disposed through the top confinement layer, but do not penetrate the active region;
• lithographically patterning a current confining ridge having a characteristic current confining width, the current confining ridge extending distally from the lateral edge of the waveguide ridge to a terminating edge;
• plasma etching current confining ridge such that the plurality of corrugations between the terminating edges and the waveguide ridge are preserved, and such that the terminating edge extends through both the top confinement layer and at least partially through the active region such that lateral current spread from said waveguide ridge is impeded from propagating beyond said terminating edge;
• vapor depositing a dielectric layer conformally atop the distributed feedback grating;
• electrodepositing a conductive contact layer atop the dielectric layer and elongated waveguide ridge;
• wherein the width of the waveguide ridge and the modulation depth and profile of the corrugations are configured such that the corrugations have a coupling coefficient sufficient to interact with the active region of the laser to impose single-mode operation and emission at specific engineered wavelengths thereon;
• and
• wherein the width of the current confining ridge is configured such that the terminating edge does not interact with the optical coupling of the waveguide ridge and the corrugations.