Effect of nonuniformity in temperature distribution on the performance of a stripe-geometry double-heterostructure laser

A theoretical model is developed to study the nonuniform temperature distribution in the laser cavity and its effect on the radiation pattern, threshold current, and emission spectrum of a gain-guiding stripe-geometry double-heterostructure laser. This model takes into account lateral current spreading, carrier out-diffusion, two dimensional heat diffusion, and the resultant gain and refractive index variation parallel to the junction planes. The effective dielectric constant method with parabolic approximation was used in solving the resulting two dimensional wave equation;Calculated results are generally in good agreement with existing experimental data. According to the model, lateral thermal guiding exists, in addition to gain-guiding, for stripe-geometry lasers under CW operation. This results in a reduction of lateral fundamental mode width and also affects the higher order mode intensity profiles. For instance, the intensity peaks of the first order lateral mode are shifted toward the center region of the stripe, thus increasing the mode gain. This may result in an optical nonlinearity at a lower radiation power level. Thermal guiding was found to be relatively important in thick active layer, narrow stripe, proton-bombarded lasers;The result also shows that the product of thermal resistance and threshold current at room temperature should be reduced to improve performance at elevated temperature. Reduction of active layer thickness up to the vicinity of 0.1 (mu)m decreases junction heating by lowering the threshold current without a substantial change in thermal resistance. For a GaAs/AlGaAs laser, a thin P-AlGaAs layer is also desirable for lower junction heating since the thickness of the layer effects thermal resistance of the device significantly. The effect of other laser dimensions, including stripe width and laser cavity length, was also included in the discussion of an optimal thermal design;The model is applicable to different stripe-geometry lasers as well as other III-V compound lasers such as the InGaAsP/InP device