Why is silicon preferred over germanium for making semiconductor devices?

Silicon is preferred because: (1) Its band gap (1.1 eV) is higher than Ge (0.7 eV), making Si devices usable up to higher temperatures (~150°C vs ~75°C for Ge). (2) Si has a higher breakdown voltage. (3) Silicon dioxide (SiO₂) formed on Si surface acts as an excellent insulating layer, useful for IC fabrication. (4) Silicon is abundantly available (from sand) and cheaper.

What is the function of the depletion region in a P-N junction?

The depletion region is a thin layer at the P-N junction where free carriers (electrons and holes) have recombined, leaving behind fixed ionised donor and acceptor atoms. It creates a built-in electric field that: (1) prevents further diffusion of majority carriers, (2) aids the drift of minority carriers, (3) acts as a potential barrier (~0.7V for Si). In forward bias this barrier is reduced; in reverse bias it is widened.

P-N Junction Diode, Rectifiers, and Transistors

Semiconductor Electronics • Class 12 Physics • NCERT • CBSE

P-N junction: depletion layer forms at junction. Forward bias reduces barrier → current flows. Reverse bias widens barrier → no current (except small reverse saturation current). Zener diode used as voltage regulator.

Key Formulas

IE = IB + IC
β = IC/IB (current gain)
α = IC/IE = β/(1+β)
R_series = (Vin − VZ)/IZ (Zener regulator)

Frequently Asked Questions

Why is silicon preferred over germanium for making semiconductor devices?: Silicon is preferred because: (1) Its band gap (1.1 eV) is higher than Ge (0.7 eV), making Si devices usable up to higher temperatures (~150°C vs ~75°C for Ge). (2) Si has a higher breakdown voltage. (3) Silicon dioxide (SiO₂) formed on Si surface acts as an excellent insulating layer, useful for IC fabrication. (4) Silicon is abundantly available (from sand) and cheaper.
What is the function of the depletion region in a P-N junction?: The depletion region is a thin layer at the P-N junction where free carriers (electrons and holes) have recombined, leaving behind fixed ionised donor and acceptor atoms. It creates a built-in electric field that: (1) prevents further diffusion of majority carriers, (2) aids the drift of minority carriers, (3) acts as a potential barrier (~0.7V for Si). In forward bias this barrier is reduced; in reverse bias it is widened.

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