TABLE OF CONTENTS With the use of modern epitaxial growth techniques (MBE, MOCVD, etc.), the alloy composition can vary on an atomic scale, and very sophisticated layer structures consisting of several barriers and wells can be constructed. Figure 7.1 gives an example for a carrier in such a structure, a so-called quantum well. Electrons in quantum wells are termed two-dimensional electron gas (2DEG) because of the confined motion in the well. The consideration of 2DEGs is very important, since such a quantum confinement is observed in modern heterostructure devices such as the GaN-based HFET as well as in the conventional silicon MOSFET [Sze (1998); Sze (2002)]. For more information on the carrier transport in heterostructures, we refer to [Ando et al. (1982); Ridley (1991)]. In the following, we summarize the most important features of the transport in a two-dimensional electron gas. We note that all these considerations are aimed at the description of a 2D system at a Al xGa 1- xN/GaN heterojunction. Hence, only these properties of 2DEGs that concern such structures will be mentioned.
