This thesis is concerned with quantum well intermixing in GaAs-AlGaAs multiple quantum well structures due to the impurity induced disordering effect using the electrically neutral impurities boron and fluorine. Particular emphasis is put on the refractive index change induced by the disordering process, and on methods of implementing this technique in the development of novel semiconductor laser structures. Selective intermixing of quantum wells is a powerful tool in the quest for developing functional integrated photonic structures. The use of impurities to enhance the interdiffusion rate of group III materials in quantum wells and barriers in well defined regions enables the creation of regions with lower optical propagation loss (< 4.5 dBcm-1).This can be utilised in low-loss waveguides for optical interconnects, extended cavity lasers, high efficiency distributed Bragg reflector lasers and more.