What are Semiconductors ?

Materials such as paper, wood, resin, etc. that block electricity are called "insulators", by contraries, those materials that conduct electricity such as copper wires/steel are called "conductors". "Semiconductors" are neither of the two and can be insulators or conductors depending on the given conditions.

The main semiconductor materials are silicon (Si) and germanium (Ge). In the periodical table of the elements they fall under the column of carbon (C). Silicon is found in sand as SiO2 and, therefore, abundantly available throughout the globe. However, silicon cannot be used as semiconductors as is. It is necessary to transform it into single-crystal carbon like that of diamonds. It looks like the process of manufacturing is not easy.
1 H
hydrogen
  2 He
helium
3 Li
lithium
4 Be
beryllium
  5 B
boron
6 C
carbon
7 N
nitrogen
8 O
oxygen
9 F
fluorine
10 Ne
neon
11 Na
sodium
12 Mg
magnesium
  13 Al
aluminium
14 Si
silicon
15 P
phosphorus
16 S
sulphur
17 Cl
chlorine
18 Ar
argon
19 K
potassium
20 Ca
calcium
21 Sc
scandium
22 Ti
titanium
23 V
vanadium
24 Cr
chromium
25 Mn
manganese
26 Fe
iron
27 Co
cabalt
28 Ni
nickel
29 Cu
copper
30 Zn
zinc
31 Ga
gallimu
32 Ge
germanium
33 As
arsenic
34 Se
selenium
35 Br
bromine
36 Kr
krypton



The atomic structure of silicon consists of a central nucleus surrounded by 2 electrons in the first orbit (K-shell), 8 electrons in the second orbit (L-shell), and 4 electrons in the third orbit (M-shell).

The 4 electrons in the outermost shell are called the valence electrons.

In a high-purity silicon crystal, each atom shares its 4 electrons with the neighboring atoms, and this sharing is called covalent bonding. Silicon is not electrically conductive because all of its electrons are bound and do not move freely.


N-type semiconductor
If a trace amount of an element with 5 electrons in the outermost shell (such as phosphorous) is added to the crystal, the excess valence electrons gained can move freely through the crystal, making it electrically conductive.


P-type semiconductor
If a trace amount of an element with 3 electrons in the outermost shell (such as boron) is added to the crystal, we obtain an electron deficiency called a hole. These holes behave like electrons, and the crystal becomes electrically conductive.



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