Current crowding (also current crowding effect, or CCE) is a nonuniform distribution of

current density In electromagnetism, current density is the amount of charge per unit time that flows through a unit area of a chosen cross section. The current density vector is defined as a vector whose magnitude is the electric current per cross-sectional ar ...

through a conductor or semiconductor, especially in the vicinity of

electrical contact An electrical contact is an electrical circuit component found in electrical switches, relays, connectors and circuit breakers. Each contact is a piece of electrically conductive material, typically metal. When a pair of contacts touch, they ca ...

s and over

PN junction PN may refer to: Arts and entertainment * ''Purple Noon'', a 1960 film * Patriotic Nigras, a griefing group in the game ''Second Life'' Business and economics * Pacific National, a rail freight company in Australia * Participatory notes, iss ...

s. Current crowding is one of the factors limiting the efficiency of

light-emitting diode A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (cor ...

s. Materials with low

mobility Mobility may refer to: Social sciences and humanities * Economic mobility, ability of individuals or families to improve their economic status * Geographic mobility, the measure of how populations and goods move over time * Mobilities, a contemp ...

charge carrier In physics, a charge carrier is a particle or quasiparticle that is free to move, carrying an electric charge, especially the particles that carry electric charges in electrical conductors. Examples are electrons, ions and holes. The term is used ...

s (e.g.,

aluminium gallium indium phosphide Aluminium gallium indium phosphide (, also AlInGaP, InGaAlP, GaInP, etc.) is a semiconductor material that provides a platform for the development of novel multi-junction photovoltaics and optoelectronic devices, as it spans a direct bandgap fro ...

(AlGaInP)) are especially prone to current crowding phenomena. It is the dominant loss mechanism in some LEDs, where the current densities, especially around the P-side contacts, reach an area of the emission characteristics with lower brightness/current efficiency. Current crowding can lead to localized overheating and formation of thermal hotspots, in catastrophic cases leading to

thermal runaway Thermal runaway describes a process that is accelerated by increased temperature, in turn releasing energy that further increases temperature. Thermal runaway occurs in situations where an increase in temperature changes the conditions in a way t ...

. Nonhomogenous distribution of current also aggravates

electromigration Electromigration is the transport of material caused by the gradual movement of the ions in a conductor due to the momentum transfer between conducting electrons and diffusing metal atoms. The effect is important in applications where high direc ...

effects and the formation of voids (see, e.g., the

Kirkendall effect The Kirkendall effect is the motion of the interface between two metals that occurs as a consequence of the difference in diffusion rates of the metal atoms. The effect can be observed for example by placing insoluble markers at the interface betwee ...

). Formation of voids causes localized nonhomogeneity of current density, and the increased resistance around the void causes further localized temperature rise, which in turn accelerates the formation of the void. Conversely, localized lowering of current density may lead to deposition of the migrated atoms, leading to further lowering of current density, further deposition of material, and formation of hillocks, which may cause short circuits. In large

bipolar junction transistor A bipolar junction transistor (BJT) is a type of transistor that uses both electrons and electron holes as charge carriers. In contrast, a unipolar transistor, such as a field-effect transistor, uses only one kind of charge carrier. A bipolar ...

s, the resistance of the base layer influences the distribution of current density through the base region, especially at the emitter side. Current crowding occurs especially in areas of localized lowered resistance, or in areas where the field strength is concentrated (e.g., at the edges of layers).

References

{{Reflist Semiconductor device defects

See also

References