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Under a high reverse-bias voltage, the p-n junction's depletion region widens which leads to a high-strength electric field across the junction. [2] Sufficiently strong electric fields enable tunneling of electrons across the depletion region of a semiconductor , leading to numerous free charge carriers .
This band alignment is due to the biasing conditions that correspond with forward-active mode; forward bias on the emitter-base junction and reverse bias on the base-collector junction. Licensing I, the copyright holder of this work, hereby publish it under the following license:
Under reverse bias, the diode equation's exponential term is near 0, so the current is near the somewhat constant reverse current value (roughly a picoampere for silicon diodes or a microampere for germanium diodes, [1] although this is obviously a function of size).
A load line diagram, illustrating an operating point in the transistor's active region.. Biasing is the setting of the DC operating point of an electronic component. For bipolar junction transistors (BJTs), the operating point is defined as the steady-state DC collector-emitter voltage and the collector current with no input signal applied.
A PN junction in forward bias mode, the depletion width decreases. Both p and n junctions are doped at a 1e15/cm3 doping level, leading to built-in potential of ~0.59V. Observe the different Quasi Fermi levels for conduction band and valence band in n and p regions (red curves). A depletion region forms instantaneously across a p–n junction.
The reverse bias safe operating area (or RBSOA) is the SOA during the brief time before turning the device into the off state—during the short time when the base current bias is reversed. As long as the collector voltage and collector current stay within the RBSOA during the entire turnoff, the transistor will be undamaged.
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In the discussion below, focus is on the NPN BJT. In what is called active mode, the base–emitter voltage and collector–base voltage are positive, forward biasing the emitter–base junction and reverse-biasing the collector–base junction. In this mode, electrons are injected from the forward biased n-type emitter region into the p-type ...