The P-N Junction Diode, Diode Applications, Bipolar
Junction Transistors (BJT), DC Biasing of the BJT Amplifier,
Transistor Modelling, Cascade Amplifier, Small-Signal BJT
Amplifier, Metal-Oxide-Semiconductor FET (MOSFET),
MOSFET Amplifier, Frequency Response of BJT and FET
Amplifiers.
Assessment
Distribution
Quiz
10%
Assignment
5%
Mid Term
20%
Lab Test
10%
Lab (Activity)
15%
Final Exam
40%
Total
100%
An atom is the smallest particle of an element that retains the characteristics of
that element.
Bohr model, atoms have a planetary type of structure that consists of a central
nucleus surrounded by orbiting electrons, as illustrated in Figure. The nucleus
consists of positively charged particles called protons and uncharged particles
called neutrons. The basic particles of negative charge are called electrons.
The atomic number equals the number of protons in the nucleus, which is the
same as the number of electrons in an electrically balanced (neutral) atom.
Atomic weight is the number of protons and neutrons in the atom’s nucleus.
For example: H-Atomic no. is 1. Atomic weight is 1.
He-Atomic no. is 2. Atomic weight is 4.
Energy Levels: Electrons orbit the nucleus of an
atom at certain distances from the nucleus.
Electrons near the nucleus have less energy than
those in more distant orbits. Only discrete
(separate and distinct) values of electron energies
exist within atomic structures. Therefore, electrons
must orbit only at discrete distances from the
nucleus. Each discrete distance (orbit) from the
nucleus corresponds to a certain energy level.
In an atom, the orbits are grouped into energy
levels known as shells. A given atom has a fixed
number of shells. Each shell has a fixed maximum
number of electrons. The shells (energy levels) are
designated 1, 2, 3, and so on, with 1 being closest to
the nucleus. The Bohr model of the silicon atom is
shown in Figure. Notice that there are 14 electrons
and 14 each of protons and neutrons in the nucleus.
.
Atomic structure: (a) germanium (b) silicon. Electrons moving around the nucleus
in orbits. Nucleus contains protons and neutrons.
Two semiconductor materials used to fabricate most diodes and transistors
are germanium (Ge) and silicon (Si).
• Similarity - each Ge and Si has 4 electrons in its outermost shell.
• Difference – Si has 14 protons but Ge has 32.
• Si is more popular as the devices that are made of Si have better
performance at higher temperature.
Valence electrons of Ge are in the 4 shell. Valence electrons of Si are in the
3 shell. Hence, Ge valence electrons are of higher energy and require smaller
amount of additional energy to escape from the atom. This property makes
Ge more unstable at high temperatures.