Chapter 14 Solutions — Semiconductor Electronics: Materials, Devices and Simple Circuits

In p-type silicon, a trivalent impurity (such as In, Al, or B) is added to pure Si.

Each trivalent dopant atom has 3 valence electrons; it forms covalent bonds with only 3 of its 4 neighbouring Si atoms, leaving one bond incomplete — a hole.

This hole is available for conduction, making holes the majority carriers.

Electrons are produced only by thermal (intrinsic) generation, so ne << nh: electrons are the minority carriers.

The dopant atoms are trivalent (acceptors), not pentavalent.

Checking the options from Exercise 14.1 applied to p-type:

(a) 'Electrons are majority carriers and trivalent atoms are the dopants' — incorrect (holes are the majority carriers).

(b) 'Electrons are minority carriers and pentavalent atoms are the dopants' — incorrect (dopants are trivalent in p-type).

(c) 'Holes are minority carriers and pentavalent atoms are the dopants' — incorrect (holes are majority carriers).

(d) 'Holes are majority carriers and trivalent atoms are the dopants' — CORRECT.

Given: Input ac frequency f = 50 Hz

Half-wave rectifier:

A half-wave rectifier allows current to pass only during one half-cycle (say the positive half-cycle) of the input ac.

For every complete input cycle, there is exactly one output pulse.

Therefore, the output frequency equals the input frequency.

Output frequency (half-wave) = 50 Hz

Full-wave rectifier:

A full-wave rectifier (centre-tap or bridge type) allows current to flow in the same direction during BOTH half-cycles of the input ac.

For every complete input cycle (period T), the output has TWO pulses (one per half-cycle).

The time period of output = T/2, so the output frequency = 2 × input frequency.

Output frequency (full-wave) = 2 × 50 = 100 Hz