In this work, the design of electrically pumped vertical cavity semiconductor optical amplifiers (eVCAs) for use in a mode-locked external-cavity laser has been developed, investigated and analysed. Four different eVCAs, one top-emitting and three bottom emitting structures, have been designed and produced, of which only the top-emitting was tested in an external laser cavity. The other designs have encountered problems either in the growth of the wafers or in the processing of the devices, leaving them with insu±cient gain for an external cavity laser. The top-emitting design does not have enough lateral current spreading to support large aperture diameters. The output power is thus very limited in these devices. The top-emitting design is, however, estimated to be able to mode-lock in an external cavity with a saturable absorber with a very low, but realisable, saturation fluence. The prospects of one of our bottom-emitting designs are good. It has an optical output power that is promising for use in an external-cavity mode-locked laser. The growth of the structure however went wrong and the structure has no net gain, which spoiled our chances to investigate it further in an external cavity. Detailed descriptions of the structure designs, clean room processing procedures and characterisations of the designs are presented in this thesis. Furthermore, comprehensive simulations of carrier distributions in the quantum well sections and the gain saturation of the different designs are performed and discussed. The thesis concludes with recommendations for further work towards the realisation of compact electrically pumped mode-locked vertical externalcavity surface emitting lasers.