English
Menu

N-Type vs P-Type Semiconductor: Key Differences Explained

An n-type semiconductor is made by adding a group V impurity (donor) such as phosphorus or arsenic to silicon, so that the extra electrons become the majority carriers. A p-type semiconductor is made by adding a group III impurity (acceptor) such as boron, so that the holes left by missing electrons become the majority carriers. The Fermi level shifts toward the conduction band in n-type material and toward the valence band in p-type material. In silicon, electron mobility is about 2 to 3 times hole mobility, so at the same doping concentration n-type material has the lower resistivity.

Aspectn-typep-type
Dopants (silicon)Group V phosphorus (P), arsenic (As), antimony (Sb)Group III boron (B). Indium and others are also used
Name and role of the impurityDonor. Gives up one electronAcceptor. Accepts one electron, creating a hole in the valence band
Charge of the ionized impurityPositive. Fixed in the lattice and immobileNegative. Fixed in the lattice and immobile
Impurity level (silicon)About 0.045 eV (phosphorus) or about 0.054 eV (arsenic) below the conduction-band edgeAbout 0.045 eV (boron) above the valence-band edge
Majority / minority carriersElectrons / holesHoles / electrons
Carrier density (fully ionized)n ≈ ND, p = ni² / NDp ≈ NA, n = ni² / NA
Fermi levelAbove the intrinsic Fermi level, toward the conduction band. Moves closer to the conduction band as doping increasesBelow the intrinsic Fermi level, toward the valence band. Moves closer to the valence band as doping increases
Majority-carrier mobility (lightly doped silicon, typical)About 1400 cm²/V·s for electronsAbout 450 cm²/V·s for holes
Resistivity at the same dopingLowerAbout 2 to 3 times higher than n-type
Where it is used in CMOSnMOS source/drain, the n-well in which pMOS is builtpMOS source/drain, the p-well in which nMOS is built. Silicon wafers for CMOS are mostly p-type

Figures are typical orders of magnitude and vary by process generation and product.

When to use which

n-type
When you want electrons to carry current. Used for nMOS source/drain, the emitter and collector of npn transistors, and the n-well in which pMOS is built.
p-type
When you want holes to carry current. Used for pMOS source/drain, the base of npn transistors, and the p-well in which nMOS is built.
Combined
Placing n-type and p-type material in contact forms a PN junction, the basis of diodes, transistors, solar cells and LEDs. In manufacturing, adding a large amount of the opposite-type impurity to an existing layer to invert its type (counter-doping) is also used.

FAQ

Since n-type semiconductors have many electrons, are they negatively charged overall?

No, they are electrically neutral overall. When a donor gives up one electron, the donor itself remains in the lattice as a positive ion, which cancels the negative charge of the electron. The same holds for p-type: the positive charge of the holes balances the negative charge of the ionized acceptors.

Are there holes in n-type material too?

Yes. In thermal equilibrium the product of electron and hole densities equals the square of the intrinsic carrier density (n × p = ni²), so with a donor concentration of 1×10¹⁶ cm⁻³ the hole density at room temperature is about 1×10⁴ cm⁻³. They are few, but these minority carriers play an important role in the operation of PN junctions and bipolar transistors.

What happens if both donors and acceptors are added?

They cancel each other out (compensation), and the material takes the type of whichever is more abundant. The carrier density is roughly set by the difference in concentrations, but mobility falls because of scattering by both kinds of ionized impurities. This property is used to invert the type when forming source/drain regions of the opposite type inside a well.

Why is the Fermi level in a different position in n-type and p-type material?

The Fermi level is the energy at which the probability of occupation by an electron is 1/2, so it reflects the carrier distribution. It shifts toward the conduction band in n-type material, which has many conduction-band electrons, and toward the valence band in p-type material, where electrons have left the valence band and holes are plentiful. In silicon at room temperature, it moves about 60 mV closer to the band edge for every tenfold increase in doping concentration.

Check your understanding

Which statement is correct when phosphorus (P) is added to silicon as an impurity?

  1. AIt becomes a p-type semiconductor with holes as majority carriers
  2. BIt becomes an n-type semiconductor with electrons as majority carriers
  3. CCarriers do not increase, and it remains an intrinsic semiconductor
Show answer and explanation

Answer: B. It becomes an n-type semiconductor with electrons as majority carriers

Phosphorus is a group V element with five valence electrons, so one electron is left over after bonding in the silicon (group IV) lattice. It is only loosely bound at a shallow level about 0.045 eV below the conduction band, so at room temperature almost all of these electrons enter the conduction band. Such impurities are called donors and produce n-type material; arsenic (As) and antimony (Sb) are also donors. To make p-type, group III elements (acceptors) such as boron (B) are added.

Which statement is correct when boron (B) is added to silicon as an impurity?

  1. AIt is electrically inactive and does not change the conductivity type
  2. BIt acts as a donor and the silicon becomes n-type
  3. CIt acts as an acceptor and the silicon becomes p-type
Show answer and explanation

Answer: C. It acts as an acceptor and the silicon becomes p-type

Boron is a group III element with three valence electrons, so it is one electron short of completing the bonds and takes one from its surroundings. This leaves a hole in the valence band and makes silicon p-type. Boron is the standard acceptor in silicon, with a shallow level about 0.045 eV above the valence band, so it is almost fully ionized at room temperature. Because it is light and diffuses quickly, shallow junctions are made with low-energy implants or BF2 implantation.

What are the majority carriers in a p-type semiconductor?

  1. AIonized acceptors
  2. BHoles
  3. CElectrons
Show answer and explanation

Answer: B. Holes

In p-type material acceptors take electrons from the valence band, creating holes, so holes are the majority carriers and electrons the minority carriers. Ionized acceptors are negative charges fixed in the lattice and cannot move. In a depletion region, however, these fixed charges are what create the electric field and built-in potential. A MOSFET forms an n-channel by gathering minority-carrier electrons at the surface of a p-type substrate (inversion).

  1. Where is the Fermi level located in an n-type semiconductor?
  2. Where in the band gap is the donor level created by phosphorus in silicon?
  3. Which correctly pairs dopants implanted into silicon with the conductivity type they produce?

Practice Semiconductor physics questions

Key terms explained

Donor
An impurity that supplies electrons to a semiconductor. For silicon, group V elements such as phosphorus (P) and arsenic (As) act as donors and make n-type semiconductors.
Acceptor
An impurity that accepts electrons from a semiconductor and creates holes. For silicon, group III elements such as boron (B) act as acceptors and make p-type semiconductors.
Fermi level
The energy at which the probability of an electron occupying a state is exactly one half. It lies closer to the conduction band in n-type material and closer to the valence band in p-type.
Mobility
How easily carriers move when an electric field is applied. In silicon, electron mobility is higher than hole mobility.
Intrinsic carrier density
The density of thermally generated electrons and holes in an undoped semiconductor, written ni. For silicon it is about 1×10¹⁰ cm⁻³ at room temperature and rises steeply with temperature. In equilibrium, n × p = ni².

Related comparisons