1. Electronics the First and Second Lectures
Second week
/ 5/ 1438 هـ
أ / سمر السلمي

2. Outline for today Office Hours Curriculum Syllabus References
Grades
Office Hours
Curriculum
Syllabus
References
Chapter One
Electronics Concepts
Atomic Structure
Explain Energy Band Theory
Composition , Structure and Lattices , Chemical Bonds of Semiconductors
Charge Carriers and Conduction Mechanisms in Semiconductors

3. Grades 5% Attendance and participation 20% Lab 15%
40% %
Attendance and participation
Lab
Homework ( from 5 to 6)
Periodic Exam ( 2 exams )
Final Exam:

4. Office Hours Time of Periodic Exams
Sunday, Tuesday and Thursday from 11 to 12 p.m.
you can put any paper or homework in my mailbox in Faculty of Physics Department
I will put any announcement or apology in my website ( , so please check it
my is for any question.
Time of Periodic Exams
The first periodic exam in / 6 / 1438 هـ 27
The second periodic exam in 4/ 8 / 1438 هـ

5. Syllabus Conduction Mechanisms in Semiconductors
Junction Diode Physical Electronics
Bipolar Junction Transistors
Field Effect Transistors
Operational Amplifiers
Digital Electronics

6. References
Electronic Principles Physics , Models and Circuits by Geray and Searle
Textbook Of Electronic Devices By Floyd (4th Edition)
Electronic devices and circuits theory by Boylestad and Nashelstky.
Microelectronics by millman and Grabel,
Electronic devices, Discrete and integrated by Fleeman
المبادئ الالكترونية فيزياء ونماذج ودوائر ترجمة د/ عبدالله شاووش
الأجهزة الإلكترونية تأليف توماس فلويد وترجمة د يسرى مصطفى و د جمال الفردغ
الالكترونيات المعـــاصرة – الجزء الأول : ياسين أحمــد الشبــول
أشباه الموصلات : مؤيــد قواسمة.
مبادئ الالكترونيات : معن عبد المجيد ابراهيم

7. Conduction Mechanisms in Semiconductors Electronics Concepts
Electronics is the science of how to control electric energy, energy in which the electrons have a fundamental role. Electronics deals with electrical circuits that involve active electrical components such as vacuum tubes, transistors, diodes and integrated circuits.
In the first Chapter, we will study conduction mechanisms in semiconductors, which is one of the main material types as division in terms of different conduction

8. Atomic Structure
An atom is the smallest particle of an element that retains the characteristics of that element. Each of the known 109 elements has atoms that are different from the atoms of all other elements. This gives each element a unique atomic structure. According to classical Bohr model, atoms have a planetary type of structure that consists of a central nucleus
surrounded by orbiting electrons, as in figure.
The electrons has negative charge. The nucleus
consists of positively charged called protons
and uncharged particles called neutrons.
Every atom has atomic number, which is the same
number of electrons and protons. The atomic
number for any element is different from other elements .

9. Atomic Structure
Each discrete distance (orbit) from the nucleus correspond to a certain energy level. These orbits are grouped into energy bands known as shells. Each sell has maximum number of electrons at permissible energy levels(orbits), as shown in the left column of table. The differences in energy levels within a shell are much smaller than the difference in energy between shells. The shells are designated 1, 2, 3 and so on, as its distance from the nucleus. In addition, some references designate shells by the letters K, L , M, as shown in the table and figure.

10. Atomic Structure
Valence electrons are electrons that are in orbits farther from the nucleus have higher energy and less tightly bound to the atom. Their shell is not complete their electrons (expect 8th group in Periodic Table) as shown in figure for Si atom, which consists 4 valence electrons
and its electron configuration
so electrons and shells divided in to
inter and outer (or valence).These valence
electrons contribute to chemical reactions
and bonding within the structure of
a material and determine its electrical
properties. As in the Periodic Table

11. Conduction Mechanisms in Semiconductors Energy Band Theory
when we study material types, we know that the main material as division in terms of different conduction are three types which are: Conductors, Insulators, and Semiconductors.
how we compare between those materials? What are their properties ?
of course, you study some of those properties over the previous years in different courses as: Electricity physics, Modern physics, and Solid State Physics 1
in Solid State Physics 1, you study Energy Band Theory. We will begin from this theory as a review.

12. The electron configuration for Oxygen atom O8 then to two atoms
Source: Dr. Abdul Aziz  Kutub

13. What about the electron configuration for N atoms ( thus, according to the number of atoms, the number of energy levels is consisted )
Source: Dr. Abdul Aziz  Kutub

14. The electron configuration for N atoms (those energy levels consists energy band)
Source: Dr. Abdul Aziz  Kutub

15. Explain Energy Band Theory
At crystal solid state consists energy levels (as of the case of isolated atoms ) . But when there are N atoms consists energy bands( which are infinitesimal numbers of energy levels that are near from each others , so it is difficult to designated between them.
every level represents energy level occupied with electrons.
in the next example in next slide, we will focus at outer shell or valence levels. Here the bonding orbital band is consisted in down part of valence levels and the bonding antiorbital band is consisted in upper part of its. Between those two bands is the energy gap, which consists Fermi level.
also we can notice that valence band is the top band from the bonding orbital band ( which is filled with electrons) and conduction band is the bottom band from the antibonding orbital band ( which is different according to material types which either empty of or partially filled with electrons).

16. Another example Si, its electron configuration is
We will focus at valence shells only (from here materials classifies conductors, insulators, and semiconductors according to Energy Band Theory)

17. bonding antiorbital band
Energy levels at outer orbitals :
The red box in the last slide
bonding orbital band
bonding antiorbital band

18. Conduction and valence bands in solid:

19. Comparison of three materials
From last slide, we notes in terms of energy band theory and electrical conductivity that :
Conductors
Insulators
Semiconductors
the energy gap is overlap that means the part of conduction band inside valence band . Because of that, we find conduction electrons in conduction band. Thus, it is a good electronic conductor. There are some conductors have very narrow energy gap and we find conduction electron in conduction band.
There is a wide gap between the conduction band and valence band . This gap is forbidden area for the existence of electrons. Thus, the conduction band is empty of electrons. This is what makes it insulated on the electrical conduction
the gap between the conduction band and valence band is narrower; but at small degrees of heat, electrons move across the gap to the conduction band and become conductive material but at a temperature of absolute zero, its behave as insulator

20. Comparison of three materials
Semiconductors
Insulators
Conductors
Example
Germanium . Silicon. Lead sulfide PdS. Cadmium sulfide CdS
Glass. Quartz. Porcelain. Alaunit. Amber. Ceramic
Metals (silver. Copper. Iron. Lead ..
bonds
Covalent or mixed bonds
Ionic bond
Metal bond
Resistivity
Medium at normal temperature in the range of from 10-5 Ω.m to 106 Ω.m
very large at room temperature in the range of 106 Ω.m to 1016 Ω.m
From 10-5 Ω.m to Ω.m
Valence band
Filled with electrons
Connection band
Completely empty of electrons in the degree of absolute zero, but it contains a number of electrons in the normal temperature or greater than absolute zero
Empty of free electrons at
normal temperatures
Partially filled with electrons at normal temperatures
Energy gap
Medium from 0.7 eV to 2 eV
very large 5 eV
Very small 0.01 eV
The effect of raising the temperature on the resistivity and conductivity
Resistance decreases dramatically. it has a moderate connectivity between metals and insulators. conductivity increases with raising the temperature
Resistance decreases but remains so large that the material fused before it becomes conductive
Increasing resistance and conductivity decreases with increasing temperature

21. Composition of Semiconductors
From those three materials, we will focus at studying about semiconductor because it is the main elementary in making vacuum tubes, transistors, ..etc. Thus, semiconductor is the main forming in electronic science.
Composition of Semiconductors
elements: from the 4th group in Periodic Table (IV) as Si and Ge
binary compounds : from the 3th and 5th group (III- V) as GaAs
:also from the 2th and 6th group (II- VI) as ZnS , 2th column here is Zn and Cd.

22. Structure and Lattices of Semiconductors
in this course, we will focus at most important structures for semiconductors.
diamond structure : it has a cube shape. in which has eight atoms at corners (eighth ), six atoms at center face of the cube (half), and four atoms inside the cube (complete). It almost as two face-centered lattices (fcc) direction (111). The elements semiconductors from the 4th group take this structure
Zincblende structure : it is similar to diamond lattice. The different is arranged of atoms, in a why one element in one of fcc lattice and the other element in the other fcc lattice) . Compounds semiconductors from the III-V , IV-IV , and some of II-VI take this structure.
diamond structure
zinc blende structure

23. Chemical Bonds of Semiconductors
As we mention at the comparison that semiconductors consist covalent or mixed bonds
Covalent bond : its for elements the 4th group as Si and Ge . it is exhibited by the diamond structure. In these crystal, each atom shares its valence electrons with its four neighbors.
Mixed bond : its for compounds as III-V and II-VI such as GaAs and ZnS. it is exhibited by the Zincblende structure. The mixed bond consist of covalent bond and ionic bond). In which the ionic bond is between the two ions in compounds , however covalent bond is between one compound and the others.
Covalent bond in Si
mixed bond in GaAs

24. Charge Carriers and Conduction Mechanisms in Semiconductors
In conductors : to understand the conduction mechanism in conductors, we can image that metal atoms immersed in sea of electrons. This electrons can move as group under the effect of electric energy.
For insulators: there is no conduction electrons in insulators because of the lack of electrons. So there are no swimming electrons in model of ionic compound ( as NaCl) ; also, because of strong of ionic bond in insulators.
negative Ion
Positive Ion

25. Charge Carriers and Conduction Mechanisms in Semiconductors
there is no conduction electrons in semiconductor at normal condition at absolute zero temperature similar to insulators because there are no swimming electrons in model . As in covalent bond for Silicon, all atoms share with four valence electrons to form the bond.
however, this situation changes ,and there
will be conduction electrons in semiconductor
according to two main factors:
rising temperature higher than absolute zero
adding impurity to intrinsic semiconductors

26. Charge Carriers and Conduction Mechanisms in Semiconductors
At rising temperature higher than absolute zero in semiconductors
We know that covalent bond is a weak bond. Thus, when the temperature raised, the bond breaks. As a result, a electron generates. This electron is the charge carrier in semiconductors similar to conductors . However, this electron leaves behind a hole .This hole has a positive charge, and it moves opposite direction than electron. Thus, by increasing rising temperatures, more electron – hole pair generate. This process happens only in semiconductors, not in conductors.

27. At rising temperature higher than absolute zero in semiconductors:
The last explanation was about the models and chemical bonds . We can also explain by energy bands. Thus, when the temperature raised, a electron receive enough thermal, energy to excited from filled valence band to empty conduction band leaving behind a hole (another charge carrier). Thus, we will notice electron – hole pair (EHP) appearance as we explain in last slide. Those charge carriers are effect factors to conduction electron in semiconductors.

28. The different between electron and hole
We study about electrons but what about holes?
Electrons flow from minus to plus, however, holes flow
from plus to minus. Therefore, they are equal in
magnitude and opposite in the direction. Because of that, electron has negative charge and hole has positive charge . Mobile hole has the same direction of current and electric field
Note (hole movement is virtual but electron movement is real)
holes
electrons
positive charge
negative charge
Energy increases going down
Energy increases going up
The same direction of electric field
The opposite direction of electric field

29. At adding impurity to intrinsic semiconductors
Another method to get charges carriers in semiconductors instead of giving excitation energy (thermal energy) is by adding impurity or doping. (what is the different between them?)
impurity is adding different atoms from the original atoms , and happened automatically in natural. However, doping is similar but we add intentional impurities in order to change its electronic properties as in increasing electron or hole numbers.
in the case of elemental semiconductors as Si, impurities either be from 3ed group (such as B) which called acceptor meaning it gives extra hole and accept extra electron, or from 5th group (such as P) which called donor meaning it gives extra electron

30. At adding impurity to intrinsic semiconductors
Also, acceptor is called extrinsic semiconductor p-type
which has higher holes concentration than electrons
concentration , and Fermi level is near valence band.
Donor is called extrinsic semiconductor n-type which
has higher electrons concentration than holes concentration
, and Fermi level is near conduction band.
The extra electron or hole
associates with positive or
negative ion by a weak bond.
Thus, it can swim freely in
crystal in case presence
thermal energy.

31. At adding impurity to intrinsic semiconductors
In case of no presence thermal energy in both n-type and p-type, the presence of impurities contribute in moving Fermi level near to two bands. As a result, possibility of electron or hole existence in it.
In the presence of a small thermal energy in extrinsic semiconductor p-type or n-type has effect in transport electron from valence band to connection band
Therefore, the presence of both impurities and thermal energy together effect more conduction mechanisms in semiconductors than the presence of one of them.

32. At adding impurity to intrinsic semiconductors
the figure below illustrates in details the role of acceptor and donor levels in case of no presence thermal energy both n-type (above) and p-type (below), and the case of presence of small thermal energy. In room temperature , we obtains complete ionization acceptor and donor atoms.

33. At adding impurity to intrinsic semiconductors
We studied in the case of elemental semiconductors such as Si and Ge impurities either
be from 3ed group which called acceptor and extrinsic semiconductor p-type
or from 5th group which called donor and extrinsic semiconductor n-type
As in the case of binary compound semiconductors such as GaAs and ZnS which consist mixed bond (ionic bond association between two elements of one compound and the covalent bond between compounds)
in the case of (III- V) compound such as GaAs impurities either
be from 2nd group (such as Mg) which called acceptor and extrinsic semiconductor p-type if it substitutes for column III (Ga) of GaAs.
or from 6th group (such as S) which called donor and extrinsic semiconductor
n-type if it substitutes for column V (As) of GaAs.

34. At adding impurity to intrinsic semiconductors
in the case of (III- V) compound such as GaAs impurities either
be from 2nd group (such as Mg) which called acceptor and extrinsic semiconductor p-type if it substitutes for column III (Ga) of GaAs.
or from 5th group (such as S) which called donor and extrinsic semiconductor
n-type if it substitutes for column V (As) of GaAs. Mg S

35. Next class review
Charge conservation law in intrinsic and extrinsic semiconductors
Drift, diffusion, recombination and generation in semiconductors