Low-threshold double heterojunction AlGaAs/GaAs laser diodes: Theory and experiment

A detailed study is presented of AlxGa1−xAs/GaAs double heterojunction lasers combining very thin recombination regions (d?0.1 μm) with high Al concentration differences at the heterojunctions. These devices have exceptionally low threshold current densities (475–1000 A/cm2 depending on the structural details), which increase by a median value of 1.35 between 22 and 70 °C. The differential quantum efficiency decrease in that same temperature interval is small. The device parameters have been analyzed in terms of available theory connecting the radiation confinement to the width of the recombination region and the dielectric step at the heterojunctions. Both the threshold current density dependence on the width of the recombination region and the far-field beam pattern are in reasonable agreement with theory. Assuming no change in carrier or optical flux confinement for large Al concentration differences, the temperature dependence of the threshold current density is found to be somewhat steeper than calculated.