Why do we need a doped substrate?

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In summary: I got it now. In summary, the doped substrate is used to assure that none of the isolation junctions will be forward biased.
  • #1
uney
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From my textbook, I know why we use the P well instead of using the p-doped substrate directly, but why do we need a doped substrate?
I think this is a stupid question, and that's why I can't find out the ans from my testbook but considered that I am a new comer in semiconductor, please help me!
 
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  • #2
It's used in order to assure that none of the isolation junctions will be forward biased.

This substrate is connected to the most negative potential to accomplish this.

Welcome to PF
 
  • #3
For an overview of the details on the process consult here:

http://en.wikipedia.org/wiki/Semiconductors
http://en.wikipedia.org/wiki/Doping_(semiconductor)

I think the problem you are having is the processes used to create components on a die. In general there are three distinctly different processes: 1) Removing substrate 2) Adding to the substrate 3) Altering the substrate. Think of the substrate like a sculpture; the sculptor begins with a block larger than the finished work. The sculpture emerges as the excess material is removed. This is the same basic process as semiconductor production. Parts of a silicon wafer are removed, doped or added to in a specific order in such a way as to leave a particular finished design with specific electrical properties.

If you have ever seen the process of PCB mfg, it is in some ways similar. In this case you start with a copper clad board. Using one of various methods you place an acid resistant layer where you want the copper to remain, then you submerge the entire board in copper-dissolving acid. When the process is complete, only the areas with acid resistance remain. You then remove the acid resist and you have a PCB.

With a silicon wafer, you choose the initial doping to best facilitate the construction of the rest of the process. If 60% of the silicone in the final die is doped in a particular way, then you might begin by doping the entire wafer to that level. In the remaining processes you mask, etch and re-dope or deposit material as required for the stage.

I hope this gives you a crude idea of the process, and the "why" of the initial doping. There is a lot of information about the various doping processes, silicon wafers and die production available on the net; some of it is fascinating reading.

Fish
 
  • #4
Thanks a lot
 

1. Why is doping necessary for substrates in electronic devices?

Doping is necessary for substrates in electronic devices because it introduces impurities into the material, altering its electrical properties. This allows for the creation of p-type and n-type materials, which are essential for the functioning of electronic devices such as diodes and transistors.

2. What is the purpose of using a doped substrate in semiconductors?

The purpose of using a doped substrate in semiconductors is to create a controllable level of electrical conductivity. This is achieved by adding impurities, or dopants, to the substrate material, which either donate or accept electrons, creating a desired level of conductivity.

3. How does doping affect the band gap of a substrate?

Doping can either increase or decrease the band gap of a substrate, depending on the type of dopant used. For example, adding a donor dopant, such as phosphorus, increases the number of free electrons, reducing the band gap and creating an n-type material. On the other hand, adding an acceptor dopant, such as boron, decreases the number of free electrons, increasing the band gap and creating a p-type material.

4. Can a substrate be doped with multiple types of dopants?

Yes, a substrate can be doped with multiple types of dopants. This is known as co-doping and is often used in the production of semiconductors to create more precise and controllable levels of conductivity. For example, a substrate may be doped with both a donor and acceptor dopant to create a material with a specific band gap and electrical properties.

5. What are some common dopants used in substrate doping?

Some common dopants used in substrate doping include boron, phosphorus, arsenic, and antimony. These elements are chosen because they have one less or one more valence electron than the substrate material, allowing them to easily donate or accept electrons and alter the material's electrical properties.

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