1. Why study the electrical properties of materials?
- We need to study the Electrical Properties of Materials because the Electrical properties of a material are those which determine ability of material to be suitable for a particular Electrical Engineering Application. Without studying that it may cause trouble because you might use a different material that is not suitable for a specific application in Electrical Engineering.
2. Why do metals possess good electrical conductivity?
- Metals are good conductors of electricity because of their free-moving delocalized electrons. When an electrical voltage is applied to a metal, an electrical field triggers the motion of electron charges. Because the electrons are delocalized, they move very easily under the influence of an electron field.
3. In terms of electron energy band structure, discuss reasons for the difference in electrical conductivity between metals, semiconductors, and insulators.
- The conductivity is based upon the number of electrons in the valence shell. Metals have an empty spot in their valence shell. This enables electrons to easily be excited to move from one band to the next. For semiconductors and insulators there are not spots available in the outer shell for an electron. This requires and electron to have enough energy to jump over into a new band. Therefore it must cover a larger gap, which requires more energy. Insulators have a larger band gap then semiconductors. The size of the band gap is therefore directly proportional to the conductivity of a material.
4. What is the distinction between electronic and ionic conduction?
- The key difference between electronic and ionic conduction is that electronic conduction is the movement of electrons from one place to another, whereas ionic conduction is the movement of ions from one place to another.
5. Briefly describe electron excitation events that produce free electrons/holes in (a) metals, (b) semiconductors (intrinsic and extrinsic), and (c) insulators.
- An electron becomes free by being excited (e.g. temperature) from a filled state to an available empty state at a higher energy (than the Fermi energy Ef). These are the e- that participate in the conduction process and are called free e-. Holes have a energy lower than Ef and are found in semicond. and insulators Small energies are required for e- excitations in metals giving rise to a large numbers of free e-greater energies are required in semiconductors and insulators, which accounts for their lower free e- concentration and thus smaller conductivity values
6. Differentiate intrinsic and extrinsic semiconducting materials. Give at least 2 examples of both intrinsic and extrinsic semiconducting materials.
- The difference between intrinsic and extrinsic semiconductor is that Intrinsic semiconductors are the pure form of semiconductor materials. Like silicon and germanium. Whereas extrinsic semiconductors are impure semiconductor formed by adding an impurity to a pure semiconductor, for example Boron and Aluminium.
7. Briefly describe the phenomena of ferroelectricity and piezoelectricity. Give at least one example for each of these phenomena.
- Piezoelectricity is electric charge that accumulates in response to applied mechanical stress in materials that have non-centrosymmetric crystal structures. For example, lithium niobate. Ferroelectric materials exhibit interesting semiconductor properties that are analogous to the properties found in stressed piezoelectric materials. For example, barium titanate