Striped GaAs lasers: Mode size and efficiency

Abstract

The stimulated efficiency of the fundamental mode and its beamwidth along the junction plane are calculated for GaAs double‐heterostructure (DH) stripe‐geometry lasers in a self‐consistent analytical model. Carrier diffusion along the junction plane creates a gain profile which acts as the guiding mechanism for the propagating mode. The size of the mode and the diffusion‐governed gain profile are the two interdependent parameters that enter into the characteristic equation whose solution determines the lasing threshold. The analytical results obtained indicate that the beamwidth is almost linearly related to the carrier diffusion length and stripe width. The minimum beamwidth obtainable for zero stripe width is ?1.3 times a diffusion length. The calculated waveguide loss, due to absorption in the unpumped region, increases with reduced stripe width. This mode loss is 5–7 cm⁻¹ for 10–12‐μm‐wide stripes, in agreement with experiment. Due to the increased waveguide loss the predicted external efficiency decreases and the lasing threshold current density increases with decrease in stripe width. The increase in threshold is due not only to carrier loss by diffusion but also to the increase in absorption loss at reduced stripe width.