Cycled Thermomechanical Failure in 808-nm High-Power AlGaAs/GaAs Laser Diode Bars

Thermomechanical cycle failure was analyzed in 808-nm high-power AlGaAs/GaAs laser diode bars (LDBs) in detail. Two thermal stress cycle experiments were carried out in these devices with peak thermal stresses of 19.4 and 33 MPa. The threshold current increase demonstrated a square-root dependence on the cycle number, and a tail and split in lasing spectrum were observed. This result was attributed to nonradiative recombination increasing with cycle number due to the diffusion of defects that accompanies band-structure renormalization. Furthermore, from X-ray diffraction measurements we found that the epitaxial layer remains monocrystalline during thermal stress cycling. We calculated the out-of-plane strain and in-plane stress induced by plastic deformation in the epitaxial layer based on the interplanar spacing in the crystal. Our results suggest that thermomechanical strain and stress were induced by pulsed operation, which led to degradation of the high-power LDBs.