Experimental and theoretical study of the spatial variation of junction voltage and current distribution in narrow stripe injection lasers

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Abstract
The spatial variation of the junction voltage and current distribution are deduced from measured profiles of the intensity of high‐frequency light across the emitting facet of stripe lasers. The dependence of voltage on current follows closely the current dependence deduced from study of the external beam. Below, threshold, the shape of the voltage profile is found to be practically independent of current. The change at threshold in the differential conductance of the junction has only a minor effect on the profile, although its effect is observable over the entire front of the coherent waves. However, there is no apparent modification of the profile connected with the structure of the coherent illumination of the facet. A new theory is developed of the current spreading in a layered structure which successfully describes the features of the measured distributions. Using only material parameters of the layers of the laser, it predicts to good approximation the observed current spreading. The modifications to the voltage profile on transit of threshold are treated as perturbations, which introduce a new parameter related to an effective total impedance of the junction. A single‐parameter fit of the theory at each power gives a good account of the corresponding profile. In principle, the parameter can be calculated, but the necessary model of the lasing modes is lacking.