Point Defects and Diffusion in Semiconductors
Solid state electronic products have become an integral part of modern day life. Integrated circuit chips fabricated using Si as the substrate material are widely used in computers, communication devices such as smart phones, and entertaining machines, as well as sensors, as dedicated and general purpose measurements, and control instruments. Lasers and light emitting devices, which are optoelectronic devices fabricated using GaAs-based compound semiconductors as substrate materials, are used in communication devices, entertaining machines, instruments or just as lights. These solid-state devices are consisting of pn-junctions produced by diffusion of n- and p-type dopant atoms, and/or heterojunctions consisting of layers of different materials that are also doped. The n- and p-type dopants are specific kinds of substitutional impurity species producing the electric carriers electrons eand holes h, respectively, in a semiconductor. Diffusion processes are also involved in controlling detrimental metallic impurity contents, in silicide formation and in thermal SiO2 growth in fabricating devices using Si. Diffusion processes in semiconductors are considerably more complicated than in metals. In this chapter, diffusion in Si and in GaAs will be fairly thoroughly discussed. Diffusion in Ge will also be mentioned for the reasons that it is the simplest case among semiconductors on the one hand while on the other its importance as a material to modify Si for the future generations of devices is emerging.
