There is a similar process for p-type semiconductors - boron, for example, only has 3 valence electrons. The terms n- and p-type doped do only refer to the majority charge carriers. Each positive or negative charge carrier belongs to a fixed negative or positive charged dopant. An n-type material by itself has mainly negative charge carriers electrons which are able to move freely, but it is still neutral because the fixed donor atoms, having donated electrons, are positive.
Similarly p-type material by itself has mainly positive charge carrier holes which are able to move relatively freely, but it is still neutral because the fixed acceptor atoms, having accepted electrons, are negative. The semiconductor has both free charge electrons and holes and immobile charge lower band electrons, nuclear protons, and ionized donors and acceptors. When a donor for example is ionized, it creates a free electron, but also it creates a positively ionized donor atom.
The charge on the free electron and the ionized donor are equal and opposite. So as long as the electron doesn't go anywhere, the net charge remains zero.
An n-type semiconductor has an excess of 'free' electrons -- electrons that can move about freely in the semiconductor very similar to electrons in a metal.
These electrons are 'donated' by immobile donor impurities doped in to the semiconductor. If you imagine starting from that state, then the result is still neutral. However since the electrons can move, they have a tendency to diffuse away from regions of high concentration.
If you connect another material e. This creates a restoring electric field, and at some point this restoring field will balance the diffusion process and an equilibrium will be obtained. The specifics of this depend on the materials, the doping and temperature, as well as any external voltage applied between the 2 materials forming the p-n junction.
Since starting from neutral , electrons negative charge have left the n-type region, it will become net positively charged, and the p-type negatively charged.
In a similar way holes 'anti-electrons' from the p-type diffuse over to the n-type, further charging it positively. A similar behaviour would occur if you connected a heavily doped n-type to a lightly-doped in fact it occurs any time there is a concentration or temperature gradient.
Since holes will "accept" free electrons, a Group 3 impurity is also called an acceptor. A semiconductor doped with an acceptor. An excess hole is now present. Because an acceptor donates excess holes, which are considered to be positively charged, a semiconductor that has been doped with an acceptor is called a p-type semiconductor; "p" stands for positive.
Notice that the material as a whole remains electrically neutral. An atom contains not only the electrons but also the nucleus which consists of an equal number of protons. Hence an atom is neutral. The reason why your doped semiconductor carries a neutral charge is because it has equal number of electrons as there are protons, be it boron doped or phosphorous doped.
While the whole crystal remains neutral, by doping you are vastly increasing the conductivity of the semiconductor.
And hence, the specialty of semiconductors and doping. Overall, the p-n crystal is neutral. If it wasn't we would immediately feel it. In fact, it is a fun exercise to calculate how many electrons would be needed to generate a substantial force equivalent to, say, the weight of a car.
The answer is surprisingly not very many. This is because the electrostatic force is relatively strong. I am mentioning this to show that the substance would probably be not stable if it had even a small imbalance in the number of positive and negative carriers. Now, when people talk about P or N doping they mean the following.
Each atom of P or N type material is also neutral. However, when placed near each other they cause interesting things to happen. Namely, one of the outer electrons of the N atom "feels" that P atom has a "hole" available more precise terminology would be a "quantum state". Due to quantum mechanical effects, there is a non-zero possibility that the electron will transition to that hole.
Once it transitions, the N now has one fewer electron and P has one extra electron. Now we have a bit of imbalance: N - slightly positive and P - slightly negative. Related Study What is Ultra Sonography? Effective uses of instruments related to Information and Communication What is Energy?
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