Growth initiation for buried-heterostructure quantum-cascade laser regrowth by gas-source molecular-beam epitaxy

• Using GS-MBE we improve the thermal conductivity in BH-QCLs regrown with InP:Fe.
• We prevent voids formation on the laser ridge sidewalls before InP:Fe.
• We obtained cw-operation up to 210 K of a 7μm-wide mid-IR BH-QCL.
• Our results are comparable to literature values obtained with regrowth by MOVPE.

We describe an optimized growth sequence for the overgrowth of quantum cascade laser ridge sidewalls with semi-insulating InP:Fe. A thin In0.52Al0.48As spacer layer grown on the laser ridge sidewalls before InP:Fe prevents the formation of void defects at this interface, which appear otherwise. Elimination of these voids at the sidewalls has led to more than a two-fold improvement of the thermal conductivity in a 7μm wide buried-heterostructure quantum-cascade laser overgrown with InP:Fe by gas-source molecular-beam epitaxy, and has allowed the continuous-wave operation of the laser up to 210 K. The measured thermal conductance is Gth=500W/Kcm2 at 210 K and Gth=1020W/Kcm2 at 127 K, comparable to the state of the art literature values obtained with regrowth by metal-organic vapor-phase epitaxy.