Room-temperature threshold-current dependence of GaAs-AlxGa1−xAs double-heterostructure lasers on x and active-layer thickness

The known properties of GaAs and AlxGa1−xAs have been used to calculate the threshold-current density of double-heterostructure (DH) lasers at room temperature without adjustable parameters. In the absence of leakage currents due to unconfined carriers, the room-temperature threshold-current density for broad-area DH lasers may be repesented by Jth (A/cm2) =4.5×103d+(20d/Γ)αi+(1/L) ln(1/R), where d is the active-layer thickness in microns, Γ is the waveguide confinement factor, αi is the internal loss, L is the cavity length, and R is the facet reflectivity. The experimentally observed increase of Jth for x0.2 given by Rode is shown to be due to the diffusive electron and hole leakage currents, and a best fit to the data was obtained with an electron minority-carrier diffusion length in AlxGa1−xAs (x≲0.3) of ∼1 μm. The above expression for Jth fits Kressel and Ettenberg’s Jth versus active-layer-thickness data at x=0.65, while for x=0.3, the experimental Jth is 300 A/cm2 larger than the calculated Jth at d=0.1 μm. This difference appears to be due to greater scattering loss at x=0.3 than x=0.6.