We discuss some basic properties of semiconductors which are crystals and consist of many atoms with periodic fashion. The energy band formation of the crystal is qualitatively presented, which leads to a concept of effective mass. We can treat electrons in conduction band as free ones using this effective mass concept. The motion of electrons in non-filled valence band can be expressed with holes with positive charge. We then evaluate intrinsic carrier concentration in crystalline silicon and energy density using semi-classical quantum theory and Fermi level is defined. The carrier concentration is controlled by donors or acceptors over a wide range. The free carries are scattered by fluctuation of periodic potential in the crystal structure. The main scattering mechanism is lattice vibration and doped impurities. This scattering is related to carrier mobility. The current and continuity equations are then derived. All these above are basic concepts used in this book.
Keywords: Acceptor, Bandgap, Boltzmann distribution function, Conduction band, Continuity equation, Donor, Effective mass, Electron, Energy density, Fermi level, Fermi-Dirac distribution function, Hole, Mobility, Poisson equation, Recombination, valence band.