45 Have you ever heard of Silicon Valley ? What is it? Can you explain why these types of semiconductors are called N-type and P-type? SEMICONDUCTORS ONLINE RESOURCES Tha Silicon Valley bond: legame to coat: rivestire doping: drogaggio layer: strato silicon: silicio Donor impurity contributes free electrons Semiconductors can be defined as materials which conduct electricity better than insulators but worse than conductors. For these characteristics, semiconductors can be used to control the flow of electric current and are widely used in electronics. Structure A typical example of a semiconductor is silicon, which is largely employed in the manufacturing of electronic components such as integrated circuits and microchips. Silicon is a pure element with low conductivity, as its four electrons in the outer orbit have strong bonds that make it difficult for them to move. However, to change the conductivity of pure silicon when needed, some substances can be added to it to change the structure of the material and its electrical properties. The process of adding other substances to pure silicon is called doping; according to the substance added, it is possible to obtain two different types of semiconductors: an N-type semiconductor is obtained by using small quantities of phosphorus or arsenic, which are substances containing five valence electrons per each atom. Four of these electrons create bonds with the silicon electrons while the extra one is free to move, allowing electric current to flow; Silicon SEMICONDUCTORS a P-type semiconductor is obtained by doping silicon with substances like boron or gallium. These elements have three valence electrons per atom, forming bonds with three of the four electrons of silicon, while the missing electron forms a hole . As electric charges naturally tend towards balance, electrons normally go to fill the holes in the atom structure; these holes are then transferred to other atoms, producing a movement of electric charges. Electrons moving from one atom to another in this way allow electric current to flow. 112 ELEcTRONIcS AND ELEcTROTEcHNOLOGY n-type Acceptor impurity creates a hole p-type Applications Semiconductors are of vital importance in many different fields of activity, from industry to healthcare, from security to household management. For example, they can be found in: electronic devices and circuits: integrated circuits components such as transistors and diodes are made of both N- and P-type semiconductors joined together; LED and OLED bulbs, which are normally coated in a thin layer of a semiconducting material to produce light; solar cells, which are made of alternating layers of N and P-type semiconductors and are used to produce photovoltaic energy.