Impurity free vacancy disordering (IFVD) using dielectric caps to induce intermixing in the GaAs/AlGaAs system is described. Silica is used to promote intermixing whilst strontium fluoride is used as a mask against intermixing. Selective bandgap-widening of GaAs/AlGaAs double quantum well laser material has been used to fabricate monolithic extended cavity strip- loaded waveguide lasers. With a differential shift of 21 nm in the wavelength of the photoluminescence peak, overall losses in the extended cavities were less than 6 cm-1 and a red-shift of the lasing spectrum with increasing passive section length is reported. Electroabsorption optical modulators integrated with passive waveguides have been fabricated using an epitaxial structure identical to that of the laser. At a wavelength of 861.6 nm, devices with a 400 μm long modulator section showed ON/OFF ratios greater than 35 dB for a reverse bias voltage of 3 V. A variation of the IFVD technique uses partial area coverage by a strontium fluoride mask under a silica cap to determine the amount of quantum well intermixing. The bandgap can then be varied at will across a wafer. Bandgap tuned lasers were fabricated using this technique. Five distinguishable lasing wavelengths were observed from five selected intermixed regions on a single chip. These lasers showed no significant change in transparency current, internal quantum efficiency or internal propagation loss, which indicates that the material quality was not degraded after intermixing.