Trying to sort out n-type vs p-type semiconductor material? The difference is the dopant: n-type carries current mainly with electrons, p-type mainly with holes. You can make either one from the same silicon.
This comparison is one part of the wider topic of semiconductor basics, which covers the ideas both materials build on.
| Item | Value |
|---|---|
| Silicon band gap | 1.14 eV |
| Phosphorus donor level in silicon (n-type) | 0.045 eV |
| Boron acceptor level in silicon (p-type) | 0.045 eV |
| Gallium acceptor level in silicon (p-type) | 0.074 eV |
The band gap comes from OpenStax University Physics Volume 3 and the dopant levels from NPTEL’s semiconductor physics notes. Figures can change between editions and sources, so check the source before you rely on them.
How doping creates n-type and p-type material
A pure silicon crystal has very few free charge carriers, because each atom shares its outer electrons in bonds with its neighbours. The explainer on what is a semiconductor covers that groundwork.
The fix is doping. Material pure to 1 part in 10 billion can have specific impurities added at about 1 part per 10 million to increase the number of carriers, according to the All About Circuits textbook. The process itself is explained in what is doping in semiconductors.
A doped crystal is called an extrinsic semiconductor. The Wikipedia article on extrinsic semiconductors notes that the doping agents are of two types, giving two types of material:
- Donor atoms release a mobile electron into the crystal, which gives n-type material.
- Acceptor atoms take an electron from the lattice and leave a hole, which gives p-type material.
N-type: extra electrons from donor atoms
Take silicon, which has four valence electrons, and swap in an arsenic atom, which has five. OpenStax explains that the extra electron has nowhere to sit in the valence band, so it goes into the conduction band (OpenStax).
That electron is only weakly bound. Its binding energy is about 0.02 eV, far below the 1.14 eV gap, so room temperature easily frees it (OpenStax).
Typical n-type dopants for silicon are group V elements. The All About Circuits textbook lists these for silicon:
- Phosphorus
- Arsenic
- Antimony
In n-type material, electrons are the majority carriers and holes are the minority carriers, as the Wikipedia article on extrinsic semiconductors puts it.
P-type: holes from acceptor atoms
P-type doping works the other way round. Aluminium has three valence electrons, so when it replaces a silicon atom it leaves a bond unfilled (OpenStax). That gap is a hole, and a neighbouring electron can move into it, which makes the hole appear to move.
Group III elements are the usual acceptors. The NPTEL notes give these acceptor energy levels in silicon:
- Boron: 0.045 eV
- Aluminium: 0.072 eV
- Gallium: 0.074 eV
- Indium: 0.157 eV
Boron is the p-type dopant for silicon, while indium is used with germanium, according to the All About Circuits textbook. In p-type material, holes are the majority carriers and electrons are the minority carriers (NPTEL).
N-type vs p-type semiconductor: side by side
| Feature | N-type | P-type |
|---|---|---|
| Dopant role | Donor | Acceptor |
| Dopant group (in silicon) | Group V | Group III |
| Example dopants | Phosphorus, arsenic, antimony | Boron, aluminium, gallium, indium |
| Majority carrier | Electrons | Holes |
| Minority carrier | Holes | Electrons |
| Name comes from | Negative charge of the electron | Positive charge of the hole |
The groups follow the host crystal. For group IV semiconductors such as silicon, group V atoms act as donors and group III atoms as acceptors (Wikipedia).
Watch the lettering. A capital P in “P-doped silicon” means phosphorus, which is a donor, so P-doped silicon is n-type, not p-type (University of Kiel).
Why do the two types matter in devices?
Neither type is better. Devices need both, because the useful behaviour happens where they meet. A p-n junction is a transition from p-type to n-type within one piece of material, and electrically it is a diode with rectifying properties (University of Kiel).
The common n-p-n bipolar transistor stacks two n-type regions around one p-type region, with metal contacts on each part (Wikipedia). Doping also lets conductivity be manipulated over many orders of magnitude, which is why one base material can serve so many roles.
Electrons and holes do not move equally easily. The All About Circuits textbook says mobility is not the same for electrons and holes, so n-type and p-type parts behave differently even at similar doping.
Doped crystals are the starting point for a long list of parts. The Wikipedia article on extrinsic semiconductors names these semiconductor electronic devices:
- Diodes
- Transistors
- Integrated circuits
- Semiconductor lasers
- LEDs
- Photovoltaic cells
Making them takes more than one uniformly doped crystal. Sophisticated fabrication processes like photolithography can implant different dopant elements in different regions of the same wafer, so n-type and p-type regions can sit side by side on one piece of silicon (Wikipedia).
The amount of dopant matters as much as the type. The concentration of doping atoms largely determines the density of charge carriers, and that density in turn determines electrical conductivity (Wikipedia). The Kiel glossary adds that conductivity can be expressed in terms of carrier density, charge and mobility, which ties back to the mobility point above (University of Kiel).
Temperature also works differently from a metal wire. Increasing temperature increases the number of electrons and holes and so decreases the resistance of a semiconductor. In metals the opposite happens, because resistance rises as electrons collide more with the crystal lattice (All About Circuits textbook).
Real devices are messier than textbook diagrams. The Kiel glossary calls the ideal abrupt p-n junction highly idealized, and says real junctions, especially in integrated circuits, do not even come close to its assumptions. Even so, the ideal results contain almost everything needed to tackle real junctions (University of Kiel).
OpenStax uses the idea of majority and minority carriers to explain how diodes and transistors operate. It also points to the Hall effect as the demonstration that holes in p-type material really exist (OpenStax).
It helps to remember where each type starts. In an intrinsic (undoped) semiconductor, the electron and hole densities are equal, according to the University of Kiel glossary. Donors tip that balance toward electrons and acceptors tip it toward holes, which is the whole difference between the two types in practical terms.
Frequently asked questions
Which is better, n-type or p-type?
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Neither. Each carries current differently, and most devices combine both, as in a p-n junction diode or an n-p-n transistor.
Is a hole a real particle?
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A hole is a state in the valence band not occupied by an electron. The University of Kiel glossary describes holes as quasiparticles that behave for practical purposes like free positively charged electrons (University of Kiel).
Do minority carriers matter?
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They exist in both types, but the number of majority carriers far exceeds the minority carriers in general (OpenStax).
Can one dopant make both types?
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In group III-V compound semiconductors, group IV atoms can act as both donors and acceptors, so they are known as amphoteric impurities. Which role they take depends on the lattice site they replace (Wikipedia).
