III-V semiconductors, of which gallium arsenide is the best known, have been important for some years and appear set to become much more so in the future. They have principally contributed to two technologies: microwave devices and optoelectronics. Recent advances in the production of thin layers have made possible a whole new range of devices based on multi-quantum wells. The heat treatments used in the manufacture of semiconductor devices means that some diffusion must take place. A good understanding of diffusion processes is therefore essential to maintain control over the technology....