Semiconductor interfaces and junctions
This chapter discusses understanding interfaces, how bulk state reasoning needs to evolve under the constraints of the surface and how these changes relate to interfaces. Interfaces and junctions connect semiconductors to the world and introduce perturbations of their own. Starting with a discussion of the SiO2-Si interface—an amorphous-crystalline interface—with its local evolution, more general conditions—of metals, insulators and semiconductors—with defect states, induced gap states and Fermi pinning are discussed. Next, neutrality level as a defining idea for the establishment of the electronic behavior of metal-semiconductor and semiconductor-semiconductor interfaces is examined. Crystalline continuity leading to heterostructures with conduction band and valence band discontinuities are developed and related to bulk bandstructure. This allows one to analytically describe and show the junction band diagrams of abrupt and graded junctions. Nitride systems often have a polarized junction, that is, have large polarization—spontaneous and often piezoelectric—whose origin is explored.