15 - Electrical Carrier Concentrations

Law of mass action

• the number of holes, p, multiplied by the # of free electrons, n, in a semiconductor, doped or not is equal to the intrinsic carrier concentration, n_i, squared

concentration of holes

• in p-type material it is approximately the same as the concentration of the acceptor (p-dopant) atoms

• In an n-type material, it is approximately the same as the concentration of the donor (n-dopant) atoms

conductivity of a semiconductor material

dependent on mobilities, µ, and concentrations, n and p, of carriers

sheet resistance, R_s

parameter given for semiconductor materials with dopant atoms diffused into semiconductor

diffused layer thickness, d

• same everywhere in the semiconductor

• controlled by temperature and time for diffusion

trace resistance, R

dependent on length and width of diffused areas

Diffusion coefficient, D

• Dopant atoms are diffused into semiconductor materials to alter electrical characteristics

• movement of defects through a crystal is governed by diffusion coefficient, D