1. Electronics 1

2. The Bohr atom The nucleus is positively charged and has the protons and neutrons. The atomic number is the number of protons and determines the particular element. In the neutral atom, the number of electrons is equal to the number of protons. Electrons are negatively charged and in discrete shells. The Bohr atom is useful for visualizing atomic structure.

3. A neutral Si atom is shown. There are 4 electrons in the valence shell. Is Si a conductor, insulator, or semiconductor? Semiconductor The valence shell The outer shell is called the valence shell. Electrons in this shell are involved in chemical reactions and they account for electrical and thermal conductivity in metals.

4. Sodium is highly reactive, and easily gives up its single valence electron. For this reason, it is not used in electrical work. The valence shell Metals have one, two or three electrons in the valence shell. The atom illustrated here is a sodium atom (Na), with only one electron in its outer shell. Sodium atom Non-metals have either complete or nearly compete outer shells, so they make poor electrical conductors.

5. Semiconductors, Insulators, Conductors 2

6. Semiconductor Materials Materials commonly used in the development of semiconductor devices: Silicon (Si) Germanium (Ge) Gallium Arsenide (GaAs)

7. Semiconductor Materials

9. Conduction in Semiconductors

13. Doping The electrical characteristics of silicon and germanium are improved by adding materials in a process called doping. n-type p-type

14. Majority and Minority Carriers Majority Carriers –The majority carriers in n-type materials are electrons. –The majority carriers in p-type materials are holes. Minority Carriers –The minority carriers in n-type materials are holes. –The minority carriers in p-type materials are electrons.

15. p-n Junctions One end of a silicon or germanium crystal can be doped as a p-type material and the other end as an n-type material. The result is a p-n junction.

16. p-n Junction The result is the formation of a depletion region around the junction.

17. p-n Junction