Can Diodes Become Nonlinear and Cause Device Failure at Reverse Breakdown?

In summary, diodes are nonlinear due to their polar nature and the biasing process. When the diode is reverse biased, there is a boundary preventing charge flow, but once the reverse breakdown voltage is reached, an exponential inverse voltage occurs. In the forward biased direction, the diode allows current to flow once the gap between the p and n regions is narrowed. This behavior is due to the thermal Boltzmann distribution of carrier energies and the exponential increase in carriers with enough energy to cross the gap. Reverse breakdown can cause the diode to melt and develop shorts, rendering it unusable.
  • #1
impendingChaos
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Why are diodes nonlinear?
 
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  • #2
They have a polar nature to them because biasing them one way helps the current to flow, but biasing them the other way (reverse bias) forms a boundary to charge flow, so very little current flows when the diode is in reverse bias.

Here's a wikipedia page in case it helps: http://en.wikipedia.org/wiki/Diode
 
  • #3
I understand the concept of the biasing but why do you have these regions of exponential change in the reverse and forward biased directions. From what I have read,when the diode is reverse biased the current which it trying to pass through it is exciting the electrons but the potential drop is too much to overcome for a time (besides the small leakage current). However, once the reverse breakdown voltage is achieved the excited electrons rush out in an exponential inverse voltage. But why is this exponential region apparent in the forward biased direction since the diode is meant to allow current to flow in that direction. For example why must silicon reach a voltage on .65 V before the current takes off so to speak? Does the diode inhibit current in the forward biased direction as well?
 
  • #4
I misspoke when I said the "current" is exciting the electrons, the current is electrons. duh
 
  • #5
The p and n regions are at different intrinsic potentials, with an energy (voltage) gap preventing current flow. The charge carriers can't flow "uphill." When you apply a reverse bias, the gap gets bigger and again no current flows (except for a little leakage). When you apply a forward bias voltage, it narrows the gap. At room temperature in Silicon, 0.6 to 0.7V sufficiently flattens the gap that carriers can flood across.

The exponential behavior comes from the thermal Boltzmann distribution of carrier energies. At room temperature some carriers have thermal (kinetic) energy, but energetic ones are exponentially less numerous than slow or stationary ones. Carriers with more energy than the gap can flow across (jump the hill), carrying a current. As you increase the forward bias voltage, exponentially more carriers have enough energy. That's why the I-V curve is exponential.
 
  • #6
BTW, at reverse breakdown the material typically melts and develops shorts, and usually the device needs to be thrown out.
 

1. Why are diodes nonlinear?

Diodes are considered to be nonlinear because their current-voltage relationship is not a straight line, unlike that of a resistor. This is due to the way diodes are designed, with a p-n junction that allows for current to flow in only one direction.

2. How does the nonlinear behavior of diodes affect electronic circuits?

The nonlinear behavior of diodes is often used in electronic circuits to control the flow of current. Diodes are commonly used as switches and rectifiers, taking advantage of their ability to only allow current to flow in one direction.

3. Can diodes be made linear?

No, diodes cannot be made linear. The p-n junction design of diodes is inherent to their functionality and cannot be altered to make them behave linearly. However, external circuitry can be used to compensate for the nonlinearity of diodes.

4. What is the reverse saturation current of a diode?

The reverse saturation current, also known as the leakage current, is the small amount of current that can flow through a diode in the reverse direction when it is reverse biased. This current is typically very small and can be ignored in most circuit designs.

5. How do temperature changes affect the nonlinear behavior of diodes?

The nonlinear behavior of diodes is affected by temperature changes. As the temperature increases, the voltage drop across a diode decreases, causing the current to increase. This is due to the change in the energy levels of the semiconductor material used in the diode's p-n junction.

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