Epitaxial design trade-offs and lateral mode profiles in hybrid III–V/Si quantum dot DBR lasers without III–V tapering

The realization of compact and energy-efficient integrated lasers operating at 1.3 μm is a key objective in silicon photonics, underpinning progress in data communications and optical interconnect technologies. Here, we revisit hybrid III–V/Si quantum-dot (QD) distributed Bragg reflector (DBR) lasers without III–V tapering, with emphasis on the epitaxial and Si waveguide thickness trade-offs imposed by standard silicon photonics. Building on our recent 220-nm-SOI waveguide-pair study, we now extend the analysis in two complementary directions. First, using supermode theory, we perform a detailed study of a gain-favorable five-QD stack with Al_0.4Ga_0.6As claddings, co-optimizing the epitaxial design together with an explicit silicon-thickness sweep, and show that 400 nm is the smallest silicon thickness in this design family that preserves the desired supermode behavior without tapering the III–V ridge. Second, motivated by the importance of 220-nm-thick silicon for CMOS-compatible photonics, we compare the published AlAs-cladding, two-QD solution with a new intermediate design using Al_0.7Ga_0.3As claddings and slightly thicker separate-confinement layers. The new 220-nm alternative preserves efficient III–V-to-Si supermode transfer while relaxing the need for pure AlAs, thereby easing epitaxial and fabrication constraints, at the cost of additional cladding leakage. Together, the three compared routes clarify a practical design landscape: strict 220-nm compatibility favors more aggressive index engineering, whereas a 400-nm silicon guide enables a significantly more gain-friendly III–V stack while still avoiding III–V tapering.