[en] The III-V semiconductors, have found their use in a broad range of technologies. Their versatility arises from the wide range of optoelectronic properties of multi-component alloys. The devices fabricated from such alloys can have highly controlled, nearly defect free (ultraclean) and entangled (complex but controlled) structures. Almost all advanced device structures rely on the development of compositionally structured materials in different dimensions. These structures are made by a process of epitaxial growth. In all epitaxial growth techniques, the substrate is kept in contact with the supersaturated environment. Liquid phase epitaxy (LPE) had been widely used in the early development of heterojunctions. However, growth from the gas phase, has become the workhorse for producing multilayer epitaxial structures. This is because such techniques are conformable to use within high throughput growth systems allowing simultaneous epitaxial growth over several wafers with a high degree of precision and uniformity