Liquid phase epitaxial grown Cd‐doped InGaAsP/InP double‐heterostructure stripe lasers were found to yield very high external differential quantum efficiency, &eegr;ext∼74% in relatively long cavity lasers compared to that of our Zn‐doped ones. Since Cd was found to diffuse only slightly into the active layer, the high &eegr;extas well as the lower threshold current in the Cd‐doped lasers are attributed to lower concentration of nonradiative recombination centers. The broad area lasers have lower &eegr;extthan the respective stripe lasers. Moreover, &eegr;extis insensitive to the heat sink temperature in the range 20–70 °C in the stripe lasers while it drops considerably in the broad area ones.