Depletion region- diode

In summary, the conversation discusses the behavior of a diode in both forward and reverse bias. In a forward bias, the complete diode model includes a 0.7V battery, a resistor, and a switch in series. This model is used because at 0.7V, the current becomes zero and increases linearly onward. However, this is not a physical phenomenon and the cut-in voltage of a diode has no relation to the built-in potential or electro-chemical potential. The equivalent circuit with a battery and other components does not exist inside the diode in reality, but is used to represent the behavior of the diode.
  • #1
azizlwl
1,066
10
At depletion layer of p region, there more negative ions thus negatively charged region.
Likewise at n region, it is positively charged.

Then why in equivalent forward bias the diode behave as a battery of .7v with positive at depletion region of the p region where it is negatively charged?
 
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  • #2
Diode never behaves like a battery.
 
  • #3
I'm reading Electronic Devices by Floyd 7edition page31- Diode Models.

In a forward bias, the complete diode model is depicted as a 0.7V battery with + polarity facing the + Vbias , a resistor and a switch all in series.

In reverse bias, only a switch which is connected parallel to a resistor.
 
  • #4
Its an approximate model of a diode. Even below 0.7V the diode current is not zero in reality. But that current is very low and can be ignored. The model has 0.7V battery so that at 0.7V the current becomes zero and increases linearly onward. This is not a physical phenomena.
 
  • #5
http://img829.imageshack.us/img829/9049/new2qm.jpg

My question is why is it that it has positive polarity even though the depletion layer of p region is negatively charged.
To my assumption it should be negative polarity.
 
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  • #6
http://ecee.colorado.edu/~bart/book/book/chapter4/ch4_3.htm
refer to fig 4.3.1 c , That is a plot of vacuum potential across the diode (at 0V bias). It is about 0.1V-0.3V for a normal pn junction and is called built-in potential. It is different from electro-chemical potential (which is what we call voltage/voltage drop for the sake of brevity). At 0V bias the voltage across the diode is always 0.

Cut-in voltage (0.7V) of a diode has no relation with built-in potential or electro-chemical potential. It is a model parameter (just like a transistor has a model parameter, beta). It just indicates the voltage below which we can very well ignore the current. Thus one can ask which equivalent circuit can follow this model? And we get the circuit with battery and all. They do not exist inside the diode in reality.
 

1. What is the depletion region in a diode?

The depletion region in a diode is the area between the p-type and n-type semiconductor materials. It is created when the two types of semiconductors are brought together and the majority carriers, such as electrons in the n-type material and holes in the p-type material, diffuse across the junction, leaving behind immobile ions. This creates a region with no free carriers, resulting in a potential barrier that prevents current from flowing in the reverse direction.

2. How does the depletion region affect the behavior of a diode?

The depletion region plays a crucial role in the functioning of a diode. It acts as a barrier for current flow in the reverse direction, allowing the diode to act as a one-way valve for electric current. When a forward bias is applied, it reduces the width of the depletion region, allowing current to flow through the diode. However, when a reverse bias is applied, the width of the depletion region increases, making it difficult for current to flow in the opposite direction, thus maintaining the diode's one-way behavior.

3. How is the depletion region related to the breakdown voltage of a diode?

The depletion region is directly related to the breakdown voltage of a diode. As the width of the depletion region increases, the electric field within it also increases. At a certain point, known as the breakdown voltage, the electric field becomes strong enough to break the covalent bonds within the depletion region, allowing current to flow in the reverse direction. The breakdown voltage is an important factor to consider when designing diodes for specific applications.

4. What is the significance of the depletion region's width in a diode?

The width of the depletion region has a significant impact on the behavior of a diode. A wider depletion region means a higher breakdown voltage and a lower leakage current, making the diode more suitable for high voltage applications. On the other hand, a narrower depletion region results in a lower breakdown voltage and higher leakage current, making the diode more suitable for low voltage applications. The width of the depletion region can be adjusted through the doping levels of the p-type and n-type materials, making it an important factor in diode design.

5. How does temperature affect the depletion region in a diode?

The width of the depletion region in a diode is affected by temperature. As the temperature increases, the thermal energy causes more free carriers to be generated, reducing the width of the depletion region and lowering the breakdown voltage. This phenomenon is known as the temperature coefficient of the breakdown voltage. It is essential to consider the effects of temperature on the depletion region when designing diodes for applications that operate in extreme temperature conditions.

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