Theoretical investigation of Jth and ηd vs. cavity length for InGaAsP/GaAs high power lasers

InGaAsP/GaAs materials are currently attracting attention for potentially reliable high-power SCH-SQW laser fabrication for 0.98 and 0.8 μm range. Scattered points show experimental results for variation of J_th and η_d vs. cavity length respectively, for lasers with different thicknesses of quantum well active layer. These features were evidenced with high reproducibility for more than 40 laser structures. These laser characteristics show anomalously strong cavity length dependence for the lasers with short cavity that cannot be explained by theoretical models used for AlGaAs lasers. The authors present new theoretical models enabling them to explain these effects. The work shows that the major factor governing the behavior of J_th and η_d of the InGaAsP/GaAs laser for a short cavity is the leakage current due to excess carriers from the waveguide layer to p-type cladding layer. The leakage current in InGaAsP/GaAs lasers is much larger than that of AlGaAs lasers due to a relatively low InGaP cladding layer band gap. Therefore a new, more sophisticated method to calculate the leakage current accurately is needed. Improved accuracy was obtained by incorporating the electric field in the cladding layer with enough accuracy for calculating the current from the drift-diffusion approximation while the electric field was obtained from the Poisson equation with physical consideration of its boundary values and approximate excess carrier density distribution in the cladding layer