THE EFFECT OF VARYING THE RIDGE WIDTH ON THE PROPERTIES OF STRAINED LAYER InGaAsP-InP QUANTUM WELL LASERS

Abstract

A study has been conducted to examine the effects of varying the ridge width on the operating characteristics of a strained-layer ridge waveguide InGaAsP-InP multiple-quantum well laser structure. A simple analytical model has been developed to explain how the input current required to reach a selected operating point changes with ridge width. It has been shown that a large portion of the current injected into the laser (as much as 60% for a 1.5pm ridge) escapes laterally from the active region. This model has been applied to lasers made from a wafer grown with 9 strained InGaAsP quantum wells on an InP substrate. The lasers themselves have a cavity length of 250pm and seven ridge widths ranging from 1.5pm to 5pm. The base temperature range investigated was from -40°C to 80°C. It has been shown that the diffusion length of the carriers within the laser decreases both with increased temperature and increased pumping. As well, the average current density in the active region at a specific operating point increases super-exponentially with temperature. The above-threshold characteristics were also examined from which the effects of the lateral current flow on the external differential efficiency were extracted. Lateral current changes little with external pumping so its effect on the differential external efficiency is minimal.