Semiconductor impurity analysis from low-frequency noise spectra

The usefulness of material for semiconductor devices can be degraded by the presence of deep impurity levels or traps which are often difficult to detect. The equations necessary for using the noise emitted by a uniform semiconductor when biased with a small dc current to find the energy, degeneracy factor, density, and time constants of such a deep level are derived. The theory was verified by an experimental study of a level in n-GaAs which was found to have an energy 0.175 eV below the conduction band and an acceptor-like degeneracy factor of 4. This technique appears to be useful for fundamental studies and as a means of monitoring material used for devices.