ABSTRACT
In this chapter, a comprehensive insight of polarization charges and 2DEG origin is presented with respect to material properties. The origin of 2DEG induced by polarization in (Aluminium Gallium nitride) AlGaN/GaN (Gallium nitride) heterostructures is demonstrated. The ab initio theory is introduced in this chapter, which takes into account the macroscopic polarization in group III nitride alloys. The sphalerite structure, with a charge central-symmetrical structure, shows no characteristics of spontaneous polarization. But in the wurtzite structure, the noncoincident center of the positive charge and negative charge leads to spontaneous polarization. Owing to the lattice misfit between constituents in the heterojunction, lattice stress or strain is generated at the heterointerface. Corresponding to the stress or strain, piezoelectric polarizations are gained. The spontaneous polarization and piezoelectric polarization in that polarization charge density are varied with respect to the rotated angle. The piezoelectric polarization is enhanced with the increase of the Al mole in AlGaN.
