Silicon recrystallization effects in mirror coatings of high-power 980-nm InGaAs/AlGaAs lasers

摘要

High-reflective PECVD Si/Si_3N_4 and IB Si/Al_2O_3 back facet coating stacks of MBE-grown, strained InGaAs/AlGaAs GRINSCH-SQW, 4-μm-wide ridge-waveguide lasers exhibit distinctive properties under laser output power. Raman microprobe spectra show that PECVD Si layers remain amorphous independent of exposure time and power applied, whereas IB Si layers rapidly recrystallize within hours and at lower power levels. Local mirror temperatures are ≈2× higher in the IB stacks than in the PECVD stacks. The refractive index of IB Si changes from 3.85 to 3.45 at 980 nm according to a transition from amorphous to crystalline Si. This reduces the reflectivity of the stack from 95 to 91%, and increases the power transmitted by the back facet by a factor of 1.7. Model experiments employing a controlled local recrystallization by external Ar~+ laser irradiation showed that recrystallization has an impact on near-field patterns and on nonlinearities in the light-current characteristics.