GaAs double heterostructure lasing behavior along the junction plane

Properties along the junction plane of GaAs double heterostructure (DH) injection lasers are studied in a self−consistent analytical model which takes into account the effect of lasing action in the active region. Solutions are obtained for the distribution of current under the stripe, and profiles of carrier concentration and gain in the active region, all as functions of lasing intensity. The results of the analysis are applied to practical situations in which the stripe width is varied from 10 to 20 μm, and the distance between the active region and the metallic stripe is varied between 0.5 and 3 μm. For these situations it is found that lasing action in the active region can exert a strong influence on the spatial distribution of the gain component of junction current. This influence increases as a function of increase in stripe width, increase in resistivity in the layer separating the active region from the stripe contact, and reduction of carrier diffusion length. In particular, it is found that as the power in the fundamental lasing mode increases the local gain decreases at the center of the stripe and increases towards the edges, thus favoring excitation of a first−order mode along the junction plane. For a 10−μm stripe width the fundamental mode is the dominant mode up to fairly large lasing power outputs, whereas for a 20−μm−wide stripe geometry a first−order mode can be excited soon after exceeding threshold. In addition, when the internal radiative differential quantum efficiency is 100%, the analysis yields a structure internal efficiency of 80%, for typical geometries used in practice. Part of the reduction in device efficiency is due to increased junction current flow, outside the lasing region, above threshold. The other part is associated with the increase in total gain current component as the lasing intensity increases. The increase in gain current is required to compensate for changes in its spatial distribution that are caused by the stimulated recombination.