Lecture on Introduction of Semiconductor at North South University as the undergraduate course (ETE411) ======================= Dr. Mashiur Rahman Assistant Professor Dept. of Electrical Engineering and Computer Science North South University, Dhaka, Bangladesh http://mashiur.biggani.org

1. Lecture 4
ETE411 :: Semiconductor

2. ATOMIC BONDING
 Ionic bond
 Covalent bond
 Metallic bond
 Van der Waals bond

3. Ionic bond
An ionic bond is a type of chemical bond that involves a metal
and a non-metal ion through electrostatic attraction. It is a bond
formed by the attraction between two oppositely charged ions.
The metal donates one or more electrons, forming a positively
charged ion or cation with a stable electron configuration. These
electrons then enter the non metal, causing it to form a
negatively charged ion or anion which also has a stable electron
configuration. The electrostatic attraction between the
oppositely charged ions causes them to come together and form
a bond.

5. Covalent bond
 Covalent chemical bonds
involve the sharing of a
pair of valence electrons
by two atoms, in contrast
to the transfer of electrons
in ionic bonds. Such bonds
lead to stable molecules if
they share electrons in
such a way as to create a
noble gas configuration for
each atom.

6. Metallic bond
 In the metallic bond, an atom achieves a
more stable configuration by sharing the
electrons in its outer shell with many other
atoms. Metallic bonds prevail in elements in
which the valence electrons are not tightly
bound with the nucleus, namely metals, thus
the name metallic bonding. In this type of
bond, each atom in a metal crystal contributes
all the electrons in its valence shell to all other
atoms in the crystal

8. Van der Waals bond
 These forces occur between the molecules of nonpolar
covalent substances such as H , Cl , and He. These
forces are generally believed to be caused by a
temporary dipole, or unequal charge distribution, as
electrons constantly move about in an atom, ion, or
molecule.
 At a given instant, more electrons may be in one
region than in another region, as illustrated in Figure.
The temporary dipole induces a similar temporary
dipole on a nearby atom, ion, or molecule. Every
instant, billions of these temporary dipoles form, break
apart, and reform to act as a weak electrostatic force
of attraction known as van der Waals forces.

10. Imperfections in Solids

12. Summery of chapter 1