The effect of lateral carrier diffusion on the modulation response of a semiconductor laser

The effect of lateral carrier diffusion upon the modulation characteristics of the semiconductor laser is investigated. A self‐consistent analysis of the spatially dependent rate equations is performed using a finite element model. The transverse junction stripe laser is treated as an example and a comparison is made between lateral carrier diffusion and spontaneous emission as damping mechanisms for the resonance peak. Experimental results bear out the conclusion that the relaxation resonance in this device is damped mainly by lateral carrier diffusion. In addition, a simple analytic result is presented which illustrates qualitatively the effect of lateral carrier diffusion upon such devices. The conclusion from this result is that lateral carrier diffusion serves to damp the relaxation resonance in the semiconductor laser quite well, but probably will not serve to improve the upper limit on modulation frequency as might have been suspected.