Current crowding
Encyclopedia
Current crowding is a nonhomogenous distribution of current density
through a conductor or semiconductor, especially at the vicinity of the contacts and over the PN junctions.
Current crowding is one of the limiting factors of efficiency of light emitting diodes
. Materials with low mobility of charge carrier
s, e.g. AlGaInP
, are especially prone to current crowding phenomena. It is a dominant loss mechanism in some LEDs, where the current densities especially around the P-side contacts reach the part of the emission characteristics with lower brightness/current efficiency. http://www.imec.be/wwwinter/mediacenter/en/SR2005/html/142516.html
Current crowding can lead to localized overheating and formation of thermal hot spots, in catastrophic cases leading to thermal runaway
. Nonhomogenous distribution of current also aggravates electromigration
effects and formation of voids (see e.g. Kirkendall effect
). 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 and further deposition of material and formation of hillocks, which may cause short circuits. http://www.csl.mete.metu.edu.tr/Electromigration/emig.htm
In large bipolar transistors, the resistance of the base layer influences the distribution of current density through the base region, especially at the emitter side. http://ece-www.colorado.edu/~bart/book/book/chapter5/ch5_4.htm
Current crowding occurs especially at the areas of localized lowered resistance, or in areas where the field strength is concentrated (e.g. at the edges of layers).
Current density
Current density is a measure of the density of flow of a conserved charge. Usually the charge is the electric charge, in which case the associated current density is the electric current per unit area of cross section, but the term current density can also be applied to other conserved...
through a conductor or semiconductor, especially at the vicinity of the contacts and over the PN junctions.
Current crowding is one of the limiting factors of efficiency of light emitting diodes
LEd
LEd is a TeX/LaTeX editing software working under Microsoft Windows. It is a freeware product....
. Materials with low mobility of charge carrier
Charge carrier
In physics, a charge carrier is a free particle carrying an electric charge, especially the particles that carry electric currents in electrical conductors. Examples are electrons and ions...
s, e.g. AlGaInP
Aluminium gallium indium phosphide
Aluminium gallium indium phosphide is a semiconductor material.AlGaInP is used in manufacture of light-emitting diodes of high-brightness red, orange, green, and yellow color, to form the heterostructure emitting light...
, are especially prone to current crowding phenomena. It is a dominant loss mechanism in some LEDs, where the current densities especially around the P-side contacts reach the part of the emission characteristics with lower brightness/current efficiency. http://www.imec.be/wwwinter/mediacenter/en/SR2005/html/142516.html
Current crowding can lead to localized overheating and formation of thermal hot spots, in catastrophic cases leading to thermal runaway
Thermal runaway
Thermal runaway refers to a situation where an increase in temperature changes the conditions in a way that causes a further increase in temperature, often leading to a destructive result...
. Nonhomogenous distribution of current also aggravates electromigration
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 direct current densities are used, such as in...
effects and formation of voids (see e.g. Kirkendall effect
Kirkendall effect
The Kirkendall effect is the motion of the boundary layer between two metals that occurs as a consequence of the difference in diffusion rates of the metal atoms...
). 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 and further deposition of material and formation of hillocks, which may cause short circuits. http://www.csl.mete.metu.edu.tr/Electromigration/emig.htm
In large bipolar transistors, the resistance of the base layer influences the distribution of current density through the base region, especially at the emitter side. http://ece-www.colorado.edu/~bart/book/book/chapter5/ch5_4.htm
Current crowding occurs especially at the areas of localized lowered resistance, or in areas where the field strength is concentrated (e.g. at the edges of layers).