The growth of 1550 nm integrated laser/modulator structures by MOCVD

Devices based upon the monolithic integration of a distributed feedback (DFB) laser with an electroabsorption modulator offer considerable promise as the next generation of sources for high speed optical communication systems. Their advantage over directly modulated diode lasers stems from the reduction of wavelength chirp, which is important for high frequency operation. One interesting route to devices of this type uses selective area epitaxy (SAE) of multi quantum well structures, to laterally pattern the band gap wavelength. This allows a low insertion loss of the laser light into the modulator to be achieved, by red shifting the laser emission wavelength with respect to the modulator band edge. This is done by fabricating the emitter in an area of perturbed epitaxy, where the quantum wells are thicker. The use of SAE can exacerbate growth imperfections which result when “difficult to grow” vertical structures are required. This paper discusses such problems, and the ways in which they can be ameliorated