ABSTRACT
In solid state physics there are generally four categories of crystalline materials: metals, semimetals, semiconductors, and insulators. For direct band gap semiconductors electrons and holes can recombine, which leads to photon emission. In semiconductors the concept of effective mass is tied to the curvature of the valence band or the conduction band near a band edge. The carrier effective mass can be measured by exposing a semiconductor sample to a magnetic field. The effect of impurities in semiconductors is how they can affect the electronic conductivity of a semiconductor. This chapter discusses the behavior of extrinsic semiconductors; that is, when there are impurities present, it is possible for them to become ionized by thermal means so that the number of carriers becomes much higher than the intrinsic carrier concentration. An ohmic contact is a kind of a junction between a metal and a semiconductor whose resistance is low enough as not to limit the current flow.
