Space-Charge Layers at Semiconductor Inferfaces

Abstract

If one puts a positive point charge into a locally neutral electron plasma (electrons on the background of fixed positive cores), the electrons in the neighborhood will rearrange to compensate that additional charge; they will screen it, such that far away from the charge the electric field vanishes. The higher the electron density, the shorter the range over which electrons have to rearrange in order to establish an effective shielding. In metals with free-electron concentrations of about 10²² cm⁻³ the screening length is short, on the order of atomic distances. On the other hand, in semiconductors the free-carrier concentrations are usually much lower, on the order of 10¹⁷ cm⁻³ may be, and we thus expect much larger screening lengths, of the order of hundreds of Ångstroms. These spatial regions of redistributed screening charges are called space charge regions.