Solid State Physics Chapter on Silicon and Germanium

Questions and Answers

In N-type semiconductors, the majority charge carriers are ______.

electrons

P-type semiconductors are created by doping with ______ elements which create holes.

acceptor

Dopant elements increase the conductivity of semiconductors by providing additional ______.

charge carriers

As temperature increases, more thermal energy allows for the creation of free ______.

electrons Signup and view all the answers

In intrinsic semiconductors, the number of free electrons, ne, is equal to the number of ______, nh.

holes Signup and view all the answers

In p-type semiconductors, the majority charge carriers are called ______.

holes Signup and view all the answers

Dopants in semiconductors create additional energy states, which can be classified as donor levels for n-type and ______ levels for p-type.

acceptor Signup and view all the answers

The abundance of majority carriers in extrinsic semiconductors helps to reduce the intrinsic concentration of ______.

minority carriers Signup and view all the answers

In n-type semiconductors, electrons come from the donor impurities, which are typically found just below the conduction band at the energy level ______.

ED Signup and view all the answers

The overall charge neutrality in a semiconductor is maintained because the additional charge carriers are equal in charge and opposite to the ionised ______.

cores Signup and view all the answers

Study Notes

Semiconductor Fundamentals

Silicon (Si) and Germanium (Ge) exhibit a diamond-like crystal structure characterized by intact covalent bonds, particularly at low temperatures.
Increasing temperature supplies thermal energy, allowing some electrons to break free from their bonds, contributing to electrical conduction.
Free electrons are accompanied by vacancies, termed holes, which carry an effective positive charge, behaving as mobile positive carriers.

Intrinsic and Extrinsic Semiconductors

In intrinsic semiconductors, the number of free electrons (ne) equals the number of holes (nh), denoted by the intrinsic carrier concentration (ni).
For p-type semiconductors, the relation shows a predominance of holes over electrons: nh >> ne.
Charge neutrality is maintained in crystals; total charge from additional carriers equals the charge of ionized lattice cores.

Doping and Its Effects

Doping introduces additional majority carriers, reducing the intrinsic concentration of minority carriers.
In n-type semiconductors, donor energy levels (ED) lie just below the conduction band (EC), allowing electrons to transition to EC easily upon ionization.
Majority carriers are generated from the dopants—pentavalent atoms produce electrons, while trivalent atoms create holes.

Energy Band Gaps

Carbon, silicon, and germanium have four valence electrons characterized by distinct energy band gaps:
- (Eg)C > (Eg)Si > (Eg)Ge.
This order indicates the variability in conductivity and energy requirements for excitation in these materials.

p-n Junction Dynamics

In unbiased p-n junctions, holes diffuse from the p-region to the n-region due to higher hole concentration in the p-region.
Factors contributing to hole diffusion include attraction from free electrons in the n-region and potential differences across the junction.
When forward bias is applied to a p-n junction, it lowers the potential barrier, facilitating current flow.

Rectification and Frequency Output

In half-wave rectification, the output frequency is equal to the input frequency; thus, a 50 Hz input results in a 50 Hz output.
Full-wave rectification doubles the output frequency compared to the input, achieving an output of 100 Hz for a 50 Hz input.

Description

This quiz focuses on the 2D and 3D representations of the diamond-like crystal structures of Silicon and Germanium, as described in the figures. It emphasizes the nature of covalent bonds and how temperature affects the crystal structure integrity. Test your understanding of these semiconductor materials and their properties.