Semiconductors & p–n Junctions — A/L Physics

What must I remember about Semiconductors & p–n Junctions?

• Intrinsic Semiconductors: Pure tetravalent crystals (Silicon, Germanium) where electrical conduction at room temperature occurs via equal concentrations of thermally generated electron-hole pairs (n_i = p_i).
• Extrinsic Semiconductors & Doping: Doping with pentavalent atoms (P, As, Sb) adds free donor electrons creating n-type semiconductor (majority carriers: electrons; minority carriers: holes); Doping with trivalent atoms (B, Al, Ga, In) creates acceptor holes yielding p-type semiconductor (majority carriers: holes; minority carriers: electrons).
• p-n Junction Formation & Depletion Layer: Majority carriers diffuse across junction (electrons to p-side, holes to n-side), leaving behind uncompensated immobile donor ions (positive) in n-region and acceptor ions (negative) in p-region, establishing a Depletion Region devoid of mobile charge carriers.
• Barrier Potential (Built-in Potential V0): The internal electrostatic field in depletion region opposes further majority carrier diffusion; Barrier potential V0 ≈ 0.7 V for Silicon and ≈ 0.3 V for Germanium at room temperature.

Test yourself (1 minute)

1. Biasing Effects on Depletion Layer

   Forward Bias (p connected to +, n connected to -): External field opposes internal barrier field, narrowing depletion layer, reducing barrier height, permitting heavy exponential majority carrier forward current; Reverse Bias (p connected to -, n connected to +): External field reinforces barrier field, widening depletion layer, blocking majority flow.

2. Reverse Saturation Current (I_s)

   In reverse bias, a minute leakage current (~nanoamperes in Si, microamperes in Ge) flows due to thermally generated minority carriers swept across junction; strongly temperature dependent.

3. Electrical Neutrality of Doped Semiconductors

   Despite being called n-type and p-type, the bulk materials remain electrically NEUTRAL overall because donor and acceptor atoms were originally neutral.

Practise Semiconductors & p–n Junctions questions today

Source: NIE G.C.E. (A/L) Physics Resource Book - Unit 9: Electronics

What comes next?

Next in the syllabus

Where does Semiconductors & p–n Junctions fit in the syllabus?

Unit 9.1 · Year 2 · Term 2