Plasma, Solid-State

a term applied by convention in physics to collections of mobile charged particles in solid conductors (conduction electrons in metals or electrons and holes in semiconductors) under conditions such that the properties of the collection are close to those of a plasma (see Figure 1). For example, on exposure to a high-frequency electromagnetic field whose frequency to is much greater than the collision frequency of the electrons, collective (plasma) effects play a greater role in the properties of semiconductors than do the collisions of electrons with each other, with phonons, with impurities, and with other crystal defects. As a result, the concepts developed in plasma research can be applied to solid-state physics.

The main difference between a solid-state plasma and a gaseous plasma is the much higher concentration n of charged particles in the former. In a gaseous plasma n ~ 10¹² cm³, in metals n ~ 10²²—10²³ cm, and in semiconductors n ~ 10¹⁵-10¹⁷ cm^-3. This fact is responsible for the difference in characteristics of solid-state and gaseous plasmas. For example, since the plasma frequency (the natural oscillation frequency of a plasma) is proportional to it is considerably greater for a solid-state plasma than for a gaseous plasma. A distinctive feature of a solid-state plasma is that it may be charged. Plasma effects in solids, particularly in semiconductors, are made use of in the creation of devices involving high-frequency technology.