Research ,how to make blue light emitting diode ?

1. Mansoura University
Faculty of Science
Physics Department
Research
Blue Light Emitting Diode
Prepared by
Mohamed Hasanin Farg
Premaster degree

2. Introduction
Energy, when we hear that word must offer thanks and respect to their
importance, It has also become a part of modern life and one cannot
think of a world without it. The most important types of energy are
electricity. Electricity has many uses in our day to day life. It is used for
lighting rooms, Modern means of transportation and communication,
battery cars are quick means of travel, radio, television and cinema.
For that important, we must be preserved, in this research will talk about
the best inventions that has earned a well-deserved Nobel Prize for
Physics, Because it helped keep the energy used in lighting by ten times
less than last use . It is Blue Light Emitting Diode.
Difference between materials
We all know the important roles of electrons in our life , but I will talk in
this research about special role of electrons in solid state material , not all
electrons but some special of them that can do that role
Talk about electrons of the most outer shell in atoms
These electrons have the stick of magic that can change any material from
type to another, how????
Solid materials divided into three types in ability of conduct electricity to
(conductors, insulator and semiconductor)
Let’s discuss about the Fermi level first. Fermi level is the energy level
taken up by an electron at the temperature range of zero Kelvin. So, at the
temperature of zero Kelvin the energy levels which are lower than i.e.
below the Fermi level are filled completely by electrons. Where below
Fermi level is valence band and above it conduction band.
Materials to be able conduct electricity, when it has some electrons in
conduction band.
In conductor (metal)
When there is in outer shell from (1 to 3) electrons material is conductors,
binding energy that bonded these electrons by nucleus is small and

3. electrons can be free by small energy in solids material (small or there is
no energy is energy gab between valence band and conduction band) and
do the role of electrical conduction. But in the insulator materials have (5
to 8) so there is high binding energy between these electrons and nucleus
and can not to be free (high energy gab between valence and conduction
band ) and can not conduct electricity ,but in semiconductors have 4
electrons that inter between conductors and insulator in ability of electric
conduction.
Types of Semiconductors
Semiconductors are mainly classified into two types: Intrinsic and
Extrinsic.
Intrinsic Semiconductor
An intrinsic semiconductor material is chemically very pure and
possesses poor conductivity. It has equal numbers of negative carriers
(electrons) and positive carriers (holes). A silicon crystal is different from
an insulator because at any temperature above absolute zero temperature,
there is a finite probability that an electron in the lattice will be knocked

4. loose from its position, leaving behind an electron deficiency called a
"hole".
If a voltage is applied, then both the electron and the hole can contribute to a
small current flow.
The conductivity of a semiconductor can be modeled in terms of the band
theory of solids. The band model of a semiconductor suggests that at ordinary
temperatures there is a finite possibility that electrons can reach the
conduction band and contribute to electrical conduction.
The term intrinsic here distinguishes between the properties of pure
"intrinsic" silicon and the dramatically different properties of doped n-type or
p-type semiconductors.
Extrinsic Semiconductor
Where as an extrinsic semiconductor is an improved intrinsic
semiconductor with a small amount of impurities added by a process,
known as doping, which alters the electrical properties of the
semiconductor and improves its conductivity. Introducing impurities into
the semiconductor materials (doping process) can control their
conductivity.
Doping process produces two groups of semiconductors: the negative
charge conductor (n-type) and the positive charge conductor (p-type).
Semiconductors are available as either elements or compounds. Silicon
and Germanium are the most common elemental semiconductors.
Compound Semiconductors include InSb, InAs, GaP, GaSb, GaAs, SiC,
GaN. Si and Ge both have a crystalline structure called the diamond
lattice. That is, each atom has its four nearest neighbors at the corners of a

5. regular tetrahedron with the atom itself being at the center. In addition to
the pure element semiconductors, many alloys and compounds are
semiconductors. The advantage of compound semiconductor is that they
provide the device engineer with a wide range of energy gaps and
mobilities, so that materials are available with properties that meet
specific requirements. Some of these semiconductors are therefore called
wide band gap semiconductors.
The Doping of Semiconductors
The addition of a small percentage of foreign atoms in the regular crystal
lattice of silicon or germanium produces dramatic changes in their
electrical properties, producing n-type and p-type semiconductors.
Pentathlon impurities
(5 valence electrons) produce n-type semiconductors
by contributing extra electrons.
Trivalent impurities
(3 valence electrons) produce p-type semiconductors
by producing a "hole" or electron deficiency
N-Type Semiconductor
The addition of Pentathlon (5) impurities such as antimony, arsenic or

6. phosphorous contributes free electrons, greatly increasing the
conductivity of the intrinsic semiconductor. Phosphorous may be added
by diffusion of phosphine gas (PH3).
P-Type Semiconductor
The addition of trivalent impurities such as boron, aluminum or
gallium to an intrinsic semiconductor creates deficiencies of
diborane6H2valence electrons,called "holes". It is typical to use B
gas to diffuse boron into the silicon material.
is a boundary or interface between two types ofn junction–pA
inside a single crystaltype-nandtype-psemiconductor material,
n junctions are–, pdoping. It is created bysemiconductorof
ductor electronicsemiconelementary "building blocks" of most

7. .LEDssuchdevices
are ableelectronsis applied to the leads,voltageWhen a suitable
within the device, releasingelectron holesto recombine with
. This effect isphotonsenergy in the form of
, and the color of the light iselectroluminescencecalled
of the semiconductor.band gapdetermined by the energy
Idea of creating Light emitting diode
optical) is anEL(Electroluminescence
in which a material emitselectrical phenomenonandphenomenon
or to aelectric currentin response to the passage of anlight
.electric fieldstrong
Electroluminescence is the result of radiative
recombination of electrons and holes in a material, usually
a semiconductor. The excited electrons release their energy
as photons - light. Prior to recombination, electrons and holes may
be separated either by doping the material to form a p-n
junction or through excitation by impact of high-energy electrons
accelerated by a strong electric field.

8. Using Gallium nitride (GaN), which is the material used to create blue
LEDs .GaN material has a direct band gap, i.e. the optical transitions
across the band gap are “allowed” and therefore much stronger than in the
case of indirect band gaps. GaN is hard to grow.
In order to make an LED you need to make a P-N junction, meaning a
layer of p-type material (positively doped) on top of n-type material
(negatively-doped). "Doping" a material is the process of changing the
carrier concentration (number of electrons or holes) and this can be done
by adding other elements with a different charge state, such as silicon
(adds an electron) or magnesium (takes an electron). Unfortunately,
adding these "dopants" introduces defects into the host material. Defects
are bad and GaN is very sensitive to certain types of defect.
Method of growth crystal of LED
ctures/layers.
Epitaxial growth results in monocrystalline layers differing from
deposition which gives rise to polycrystalline and bulk structures.
Epitaxy types:
Homoepitaxy: Substrate & material are of same kind.
(Si-Si)
Heteroepitaxy: Substrate & material are of different kinds. (Ga-
As)

9. Epitaxy Techniques
 Vapor-Phase Epitaxy (VPE)
 Modified method of chemical vapor deposition (CVD).
 Undesired polycrystalline layers
 Growth rate: ~2 µm/min.
 Liquid-Phase Epitaxy (LPE)
 Crystal layers are from the melt existent on the substrate.
 Hard to make thin films
 Growth rate: 0.1-1 µm/min.

10.  Molecular Beam Epitaxy (MBE)
 Relies on the sublimation of ultrapure elements, then
condensation of them on wafer
 In a vacuum chamber (pressure: ~10-11
Torr).
 “Beam”: molecules do not collide to either chamber walls or
existent gas atoms.
 Growth rate: 1µm/hr.
Start to made GaN crystals by HVPE
At the end of the 1960s, GaN crystals were more efficiently produced by
growing GaN on a substrate using the HVPE technique (Hydride Vapour
Phase Epitaxy). There are some problems in this method. The surface
roughness was not controlled, the HVPE-grown material was
contaminated with transition metal impurities and p-doping was
passivated due to the presence of hydrogen, forming complexes with
acceptor dopants. The role of hydrogen was not understood at that time.
The major goals in the technology of GaN should be: (1) the synthesis of
strain free Single crystals, (2) the incorporation of a shallow acceptor in
high concentrations" (to provide effective p-doping).
New growth techniques
In the 1970s, new crystal growth techniques, MBE (Molecular Beam
Epitaxy) and MOVPE (Metalorganic Vapour Phase Epitaxy) were
developed. Efforts were made to adapt these techniques for growing GaN.
MBE: Working Principle
 Epitaxial growth: Due to the interaction of molecular or atomic
beams on a surface of a heated crystalline substrate.
 The solid source materials sublimate
 They provide an angular distribution of atoms or molecules
in a beam.
 The substrate is heated to the necessary temperature.
 The gaseous elements then condense on the wafer where
they may react with each other.
 Atoms on a clean surface are free to move until finding correct
position in the crystal lattice to bond.

11.  Growth occurs at the step edges formed: More binding forces at an
edge.
Isamu Akasaki began studying GaN as
a) Growth of GaN on sapphire using an AlN layer.
b) Resistivity of Mg doped GaN as a function of annealing temperature.
The breakthrough was the result of a long series of experiments and
observations. A thin layer (30 nm) of polycrystalline AlN was first
nucleated on a substrate of sapphire at low temperature (500 °C) and then
heated up to the growth temperature of GaN (1000 °C) . During the
heating process, the layer develops a texture of small crystallites with a
preferred orientation on which GaN can be grown. The density of
dislocations of the growing GaN crystal is first high
, but decreases rapidly after a few nm growths. A high quality surface
could be obtained, which was very important to grow thin multilayer
structures in the following steps of the LED development. In this way,

12. high quality device-grade GaN was obtained for the first time. GaN could
also be produced with significantly lower background n-doping.
Main applications of blue GaN LEDs
Traffic signals
Automotive head lamps
Backlighting for liquid crystal displays (LCD)
Mobile phones
Laptop computers
Desktop computers
TVs
General lighting
Industrial
Street lighting

13. References
.Article of Nobel Prize 2014 in physics
. Shuji Nakamura, Gerhard Fasol, Stephen J Pearton “The Blue Laser
Diode: The Complete Story” ISBN 3540665056, Springer-Verlag,
(Second Edition, September 2000)
.http://iramis.cea.fr/en/Phocea/Vie_des_labos/Ast/ast_sstechnique.php?id
_ast=494