TABLE OF CONTENTS Epitaxial growth techniques involve the growth of the active (those that are part of the device) semiconductor films, usually less than 1% of the total substrate thickness, for a device of interest on a suitable substrate. The use of epitaxial techniques allows more flexibility in the growth and placement of semiconducting layers and dopants than is achieved by other techniques such as bulk crystal growth, ion implantation and diffusion. Bandgap engineering becomes possible by choosing an arrangement of different semiconductor layers so that the bandgap along the growth direction is tailored to achieve certain desired properties. The substrate provides a template, usually of the same crystal structure and lattice constant (atomic spacing), for high-quality crystalline growth. For example, GaAs on GaAs, InGaAs on InP and SiGe on Si are all common types of epitaxy along with many other variants. Elemental constituents of the film to be grown are brought into contact with the substrate surface at elevated temperatures under conditions optimised for the particular growth technique. Impurity dopants may be introduced with the elemental constituents to dope particular layers. Generally, the quality of the epitaxial layers is much higher than that of the underlying substrate. Although crystal defects in the substrate can propagate into an epitaxial layer, they tend to diminish in number as the growth continues. For this reason, active layers of a device are normally grown only after growth of a suitable thickness of a "buffer" layer that filters out defects.
Epitaxial growth involves the optimisation...
