| Current Crowding |
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Current crowding is one of the limiting factors of efficiency of Light Emitting Diodes . Materials with low mobility of Charge Carrier s, eg. AlGaInP , are especially prone to current crowding phenomena. It is a dominant loss mechanisms 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. {Link without Title} Current crowding can lead to localized overheating and formation of thermal Hot Spot s, in catastrophic cases leading to Thermal Runaway . Nonhomogenous distribution of current also aggravates Electromigration effects and formation of voids (see eg. Kirkendall Effect ). Formation of voids causes localized nonhomogenity 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. {Link without Title} In large Bipolar Transistor s, the resistance of the base layer influences the distribution of current density through the base region, especially at the emitter side. {Link without Title} Current crowding occurs especially at the areas of localized lowered resistance, or in areas where the field strength is concentrated (eg. at the edges of layers). |
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