A p-type semiconductor is silicon (Si) or germanium (Ge) doped with a trivalent impurity such as boron (B), aluminium (Al) or indium (In). The dopant has only 3 valence electrons, so one covalent bond is left incomplete, creating a hole. Holes become the majority carriers and electrons the minority carriers. Memory hook: p-type = "positive holes plenty" from trivalent (3-electron) dopants.
Left: a trivalent boron atom bonds with only 3 of the 4 neighbouring silicon atoms, leaving one bond incomplete, which is a mobile hole. Right: the energy band view shows the acceptor level EA sitting just above the valence band top Ev, so valence electrons easily jump up and leave holes behind, making holes the majority carriers.
Your doubts, answered
Is a p-type semiconductor positively charged overall?
No. A p-type semiconductor is electrically neutral. It has plenty of positive holes, but each trivalent dopant atom (called an acceptor) becomes a fixed negative ion after it accepts an electron. The mobile positive holes and the fixed negative ions cancel out, so the net charge is zero. 'p' stands for the positive holes that carry current, not for the overall charge.
Why are holes the majority carriers in a p-type semiconductor?
The trivalent dopant (like boron) has only 3 valence electrons. It bonds with 3 of the 4 neighbouring Si atoms, but the fourth bond has a vacancy, which is a hole. Each dopant atom adds one hole. Because we add many dopant atoms, the number of holes becomes much larger than the few thermally-generated electrons. So holes are the majority carriers and electrons are the minority carriers.
Which dopants make a p-type semiconductor?
Trivalent atoms (valency 3) from Group 13 of the periodic table: boron (B), aluminium (Al), indium (In). They have one valence electron less than Si or Ge. NEET tip: pentavalent atoms like arsenic (As), antimony (Sb) and phosphorus (P) give n-type, not p-type. Boron doped in germanium gives p-type (asked in NEET 2023).
Are there any electrons in a p-type semiconductor?
Yes. Electrons are still present as minority carriers. They are produced by thermal breaking of covalent bonds, exactly as in an intrinsic semiconductor. Their number is small compared to the holes. By the mass action law, ne x nh = ni squared, so when holes (nh) go up by doping, the electrons (ne) go down, but never become zero.
What is an acceptor atom and the acceptor energy level?
A trivalent dopant is called an acceptor because it accepts an electron from the valence band to complete its fourth bond. In the energy band picture, it creates an acceptor level EA slightly above the top of the valence band EV. With very small energy, an electron from the valence band jumps to EA (leaving a hole behind), so the acceptor becomes a negative ion and a hole is released into the valence band.
⚠️ The NEET trap ✗ p-type is doped with pentavalent atoms and its majority carriers are electrons. ✓ p-type is doped with TRIVALENT atoms (B, Al, In) and its majority carriers are HOLES. Pentavalent dopants and electron majority carriers describe n-type. 🧠 Remember: p-type = 3 valence electrons (trivalent) = Holes. Don't swap n and p. NEET 2019 option D used this exact trap.
Real NEET questions
NEET 2019
For a p-type semiconductor, which of the following statements is true?
A · Electrons are the majority carriers and trivalent atoms are the dopants
B · Holes are the majority carriers and trivalent atoms are the dopants ✓
C · Holes are the majority carriers and pentavalent atoms are the dopants
D · Electrons are the majority carriers and pentavalent atoms are the dopants
Solution: Step 1: p-type is made by doping Si or Ge with a trivalent (3 valence electron) impurity such as B, Al or In. So the dopants are trivalent. Step 2: Each trivalent atom leaves one bond incomplete, creating a hole. So holes are the majority carriers. Combining both facts gives: holes are majority carriers and trivalent atoms are the dopants. Answer: B.
NEET 2023 Phase 2
A p-type extrinsic semiconductor is obtained when Germanium is doped with:
A · Arsenic
B · Boron ✓
C · Antimony
D · Phosphorous
Solution: Step 1: A p-type semiconductor needs a trivalent (acceptor) dopant. Step 2: Check valency of each option. Arsenic, Antimony and Phosphorus are pentavalent (valency 5) - they give n-type. Boron is trivalent (valency 3). Step 3: Therefore germanium doped with boron gives a p-type semiconductor. Answer: B.
NEET 2021
The electron concentration in an n-type semiconductor is the same as the hole concentration in a p-type semiconductor. An external electric field is applied across each of them. Compare the currents in them.
A · Current in n-type > current in p-type ✓
B · No current will flow in p-type, current will only flow in n-type
C · Current in n-type = current in p-type
D · Current in p-type > current in n-type
Solution: Step 1: Current density J = n e v_drift = n e (mu) E. With equal carrier concentration n and equal field E, current is proportional to mobility mu. Step 2: In the n-type the carriers are electrons (mobility mu_e); in the p-type the carriers are holes (mobility mu_h). Step 3: Electron mobility is greater than hole mobility, mu_e > mu_h, because holes move by a slower bond-to-bond hopping. Step 4: So the n-type carries the larger current. Answer: A.
It is a semiconductor (Si or Ge) mixed with a small amount of trivalent atoms like boron. This adds extra holes. The holes carry the current, so it is called p-type, where p stands for positive holes.
Why is it called p-type?
Because the majority current carriers are positively charged holes. The letter p comes from 'positive'. It does not mean the crystal has a net positive charge; it stays electrically neutral.
What are the majority and minority carriers in a p-type semiconductor?
Holes are the majority carriers (from the trivalent dopant) and electrons are the minority carriers (from thermal generation).
Give three examples of trivalent dopants used for p-type.
Boron (B), aluminium (Al) and indium (In). All belong to Group 13 and have 3 valence electrons, one less than Si or Ge.
Does adding trivalent dopant increase or decrease conductivity?
It increases conductivity. Doping adds many extra holes, so more mobile carriers are available, and the resistivity of the semiconductor falls sharply compared to the pure (intrinsic) sample.
What is the acceptor energy level EA?
It is an energy level created just above the valence band top EV by the trivalent dopant. Electrons from the valence band easily jump to EA, leaving mobile holes in the valence band.
