• In this Chapter will learn about
• SEMICONDUCTOR MATERIALS: Ge, Si, AND GaAs
• COVALENT BONDING AND INTRINSIC MATERIALS
• ENERGY LEVELS
• n -TYPE AND p -TYPE MATERIALS
• SEMICONDUCTOR DIODE
• IDEAL VERSUS PRACTICAL
3. What are SemiConductors
• Semiconductors are a special class of elements
having a conductivity between that of a good
conductor and that of an insulator.
• There are two types of semiconductors:
Single Crystal Semiconductor:
• Examples : Germanium (Ge) and Silicon (Si)
have a repetitive crystal structure
• Examlpes : Gallium Arsenide(GaAs),Cadmium
Sulfide (CdS),are constructed of two or more
semiconductor materials of different atomic structures.
4. Uses of Semiconductor
• The three semiconductors used most frequently in
the construction of electronic devices are Ge, Si, and
5. COVALENT BONDING
• A covalent bond, also called a molecular bond, is a
chemical bond that involves the sharing of electron pairs
• Semiconductors also form Covalent bonds
• An intrinsic semiconductor is an undoped semiconductor.The
term intrinsic is applied to any semiconductor material that has
been carefully refined to reduce the number of impurities to a
very low level—essentially as pure as can be made available
through modern technology.
7. ENERGY LEVELS
• Electrons are found in areas called shells. A shell is
sometimes called an energy level.
• The farther an electron is from the nucleus, the
higher is the energy state, and any electron that has
left its parent atom has a higher energy state than
any electron in the atomic structure.
• An electron in the valence band of silicon must absorb more energy
than one in the valence band of germanium to become a free carrier.
Similarly, an electron in the valence band of gallium arsenide must
gain more energy than one in silicon or germanium to enter the
9. n -TYPE AND p -TYPE
• A semiconductor material that has been subjected to
the doping process is called an extrinsic material.
• There are two types of Extrinsic material in
• n -TYPE AND p -TYPE
10. n -TYPE AND p -TYPE
n -TYPE p -TYPE
• An n -type material is created by
introducing impurity elements that
have five valence electrons
(pentavalent) such as antimony ,
arsenic , and phosphorus.
• The p -type material is formed by
doping a pure germanium or
silicon crystal with impurity atoms
having three valence electrons.
The elements most frequently
used for this purpose are boron , g
allium , and indium
• A semiconductor diode is a device typically made from
a single p–n junction. At the junction of a p-type and an
n-type semiconductor there forms a depletion region
where current conduction is inhibited by the lack of
mobile charge carriers.
• This region of uncovered positive and negative ions is called the
depletion region due to the “depletion” of free carriers in the region.
13. Types of Semiconductor
Forward Biased Reverse Biased
• A forward-bias or “on” condition is
established by applying the positive
potential to the p -type material and
the negative potential to the n -type
material as shown in Fig
• If an external potential of V volts is
applied across the p – n junction such
that the positive terminal is connected
to the n -type material and the
negative terminal is connected to the p
-type material as shown in Fig
14. IDEAL VERSUS
Ideal Diode Practical Diode
• An ideal diode is a diode that acts like
a perfect conductor when voltage is
applied forward biased and like a
perfect insulator when voltage is
applied reverse biased.
In a practical diode there is very little
forward current until the barrier
voltage is reached. When reverse bias
only a small amount of current flows
as long as the reverse voltage is less
than the breakdown voltage of the