Waveguide-confining layer with gain medium to emit subwavelength lasers, and method to form same

A photonic integrated circuit (PIC) die comprising:

• a semiconductor substrate;
• a buried insulator layer on the semiconductor substrate;
• an oxide layer over the buried insulator layer;
• a silicon-based optical confinement structure embedded within or positioned on the oxide layer;
• a first blocking layer and a second blocking layer over the oxide layer and separated from each other and separated by a horizontal slot, wherein each of the first blocking layer and the second blocking layer includes a metal or a nitride;
• a gain medium on the oxide layer and within the horizontal slot between the first blocking layer and the second blocking layer, the gain medium including a material having a lower refractive index than each of the first blocking layer and the second blocking layer,
• wherein the gain medium is vertically aligned with the silicon-based optical confinement structure, and a portion of the oxide layer separates the gain medium from the silicon-based optical confinement structure,
• wherein an upper surface of the gain medium is substantially coplanar with an upper surface of each of the first blocking layer and the second blocking layer, and a lower surface of the gain medium is substantially coplanar with a lower surface of each of the first blocking layer and the second blocking layer;
• a nitride layer within the oxide layer, the nitride layer positioned vertically between the gain medium and the silicon-based optical confinement structure;
• a waveguide optically coupled to the silicon-based optical confinement structure;
• and
• a back-end-of-line (BEOL) stack over the gain medium and the first blocking layer and the second blocking layer, wherein the BEOL stack includes a light source in optical alignment with the gain medium.