Semiconductors ch. 1

SEMICONDUCTORSUNIVERSITY OF ANBAR – COLLEGE OF SCIENCE

DEPT. OF PHYSICS

MAZIN A. AL- ALOUSI

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:The date of the lecture : We. Every week 8:00 PM

10 marks quizzes

10 marks H.W.s

30 marks Monthly exams

Calculated scores

Semiconductors - Ch. 1 ........By : M. Al-Alousi

3 Semiconductors - Ch. 1 ........By : M. Al-Alousi


…………….. : General introduction Chapter 1 : The Crystal Structure of Solids Chapter 2 : Introduction to Quantum MechanicsChapter 3 : Introduction to the Quantum Theory of Solids Chapter 4 : The Semiconductor in Equilibrium Carrier Transport Phenomena Chapter 5 : Nonequilibrium Excess Carriers in Semiconductors Chapter 6 : The pn Junction Chapter 7 : The pn Junction Diode Chapter 8 : Metal-Semiconductor and SemiconductorChapter9 : HeterojunctionsChapter 10 : The Bipolar TransistorChapter 11 : Fundamentals of the Metal-Oxide-Semiconductor and Field-Effect Transistor Chapter 13 : Metal-Oxide-Semiconductor Field-Effect Transistor , Additional ConceptsChapter 12 : The Junction Field-Effect Transistor Chapter 14 : Optical Devices Chapter 15 : Semiconductor Power Devices

The Syllabus Of Semiconductor Subject


General Introduction

• The electrical resistance (R) of an electric conductor is a measure of the difficulty to pass an electric current through that conductor. ( It is measured by ohm unit Ω).

• The electrical resistivity (ρ)(also known as resistivity, specific electrical resistance, or volume resistivity) is a quantity of strongly a given material opposes the flow of electric current. The SI unit of electrical resistivity is the ohm metre (Ω m)⋅ ⋅

• Important concepts

• The electrical conductance (G) is the ease with which an electric current passes. The electrical conductance is measured in Siemens (S).

• The Electrical conductivity (σ) or specific conductance is the reciprocal of electrical resistivity, and measures a material's ability to conduct an electric current. Its SI unit is Siemens per meter (S/m) and CGSE unit is reciprocal second (s−1).

𝑅=𝑉𝐼 →Ω=

𝑣𝑜𝑙𝑡𝑎𝑚𝑝𝑒𝑟 ,𝐺=

𝐼𝑉 →𝑆=

𝑎𝑚𝑝𝑒𝑣𝑜𝑙𝑡𝑟 , 𝜌=𝑅 𝐴

𝑙 → 𝛺 .m

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What Are The Semiconductor Materials ?

Metals

Semiconductors

Semimetals

CuNa

K

As

Sb

Graphite

Bi

Ge (pure)1013

1014

1015

1016

1017

1018

1019

1020

1021

1022

1023

Metals: s > 105 (W.m)-1 or S Semiconductors: 10-6 < s < 105 (W.m )-1

Insulators: s < 10-6 (W.m )-1

Then ……..The Semiconductors are materials which have an Electrical Conductivity between the conductors, and the insulators

Electrical Conductivity of materials

The conduction electrons concentrations


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The Crystal Structure of

Solids

C H A P T E R 1


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1.1 : Semiconductor Materials 1.2 : Types of Solids

1.3 : Space Lattices 1.3.1 : Primitive and Unit Cell 1.3.2 : Basic Crystal Structures

1.3.3 : Crystal Planes and Miller Indices 1.3.4 : The Diamond Structure

1.4 : Atomic Bonding 1.5 : Imperfections and Impurities in Solids

1.5.1 : Impegections in Solids 1.5.2 : Impuritler m Solids

1.6 : Growth of Semiconductor Materials 1.6.1 : Growth from a Melt

1.6.2 : Eptaxtul Growth

C H A P T E R 1

The Crystal Structure of Solids


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A semiconductor may be as an elements or compounds

• IV-VI (PbSe, SnTe)• III-V (GaAs, InP, InSb)

• II-VI (CdS, HgTe, ZnTe, ZnO).

1.1 : Semiconductor Materials


10Semiconductors - Ch. 1 ........By : M. Al-Alousi

Why Silicon:

The semiconductors have been used before 1949 a s a diodes in the rectifier and photodiode applications.

In the firsts of 50s of last century, the germanium has been widely used as a semiconductor materials, but it wasn’t efficient with many applications , because of its leakage current at not significantly high temperatures. Then, it was been replaced by Silicon.

Advantages of Silicon:

1. Infinitesimal of leakage current is the Si devices.2. The easily configure of the high quality silicon by the thermal growth method.3. Si is the cheapest in the present time

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1.2 : Types of Solids

Completely ordered In segments

Entire solid is up of atoms in an orderly array

No recognizable Long – range order


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1.3 : Space Lattices

The lattice is the periodic arrangement of atoms in the crystal

1.3.1 : Primitive and Unit Cell

a1

b1

Two-dimensional representation of a single-crystal lattice

a1

b1

A

a2

b2

B

a3

b3

C

a4

b4

D

Two-dimensional representation of a single-crystal lattice showing various possible unit cells.

A primitive cell is the smallest unit cell that can be repeated to form the lattice

A generalized primitive unit cell

𝒓 =𝒑𝒂+𝒒𝒃+𝑺𝒄……….(𝟏)

Where p, q, and s are integers

Every equivalent lattice point in the three- dimensional crystal can be found using the vector ( r ):


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1.3.2 : Crystal Structures

1 -The simple Cubic Lattice :

This lattice consist on one atom

a b

c

a = b = c𝛼=𝛽=𝛾=90 𝑜

𝟏𝟖

𝒕𝒉𝒆 𝒗𝒍𝒖𝒎𝒆𝒐𝒇 𝒍𝒂𝒕𝒕𝒊𝒄𝒆𝒊𝒔𝑽=𝒂𝟑

: is the radius of atom

a = 2r

2r

2r

A

B

C

𝑨𝑨𝑭=𝟒𝝅𝒓𝟑𝟑 (𝟐𝒓)𝟑

𝑨𝑨𝑭=𝝅𝟔


Polonium is the only element has this system

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2 -The body-centered cubic Lattice :

This lattice consist on two atoms

a = b = c𝛼=𝛽=𝛾=90 𝑜



A

B

C

4ra

(𝐴𝐵)2=(𝐵𝐶)2+(𝐶𝐴)2

(4𝑟 )2=(√2𝑎)2+𝑎2(4𝑟 )2=3𝑎2(4𝑟 )2=3𝑎216𝑟 2=3𝑎2

or

(𝑯 .𝑾 ) 𝒇𝒊𝒏𝒅 𝑨𝑨𝑭 𝒐𝒇 𝑩𝑪𝑪 𝒍𝒂𝒕𝒕𝒊𝒄𝒆

√𝟐𝒂

Semiconductors - Ch. 1 …………………………………………………………………………………………………………………………………......By : M.azin Al-Alousi

As the sodium (Na) and the tungsten (W)

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3 -The face-centered cubic Lattice :

This lattice consist on four atoms

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a = b = c𝛼=𝛽=𝛾=90 𝑜



( prove that: )


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The fourteen space lattices (Bravais lattices) :

Find the volume density of atoms in a body-centered cubic crystal, if a = 5 x 10-8cm

Example:

Solution :

𝐷𝑒𝑛𝑠𝑖𝑡𝑦=𝑁𝑜 .𝑜𝑓 𝐴𝑡𝑜𝑚𝑠

𝑉𝑜𝑙𝑢𝑚𝑒𝑜𝑓 𝑙𝑎𝑡𝑡𝑖𝑐𝑒

𝐷𝑒𝑛𝑠𝑖𝑡𝑦=2

(5 x 10−8 )3

¿1 .6×1022𝑎𝑡𝑜𝑚 /𝑐𝑚3

(): (1.2, 1.3, 1.12 and 1.14) in Semiconductor Physics and Devices(Donald A. Neamen) p.p.(21-22)


1.3.3 : The lattice’s planes :

The lattice’s planes are explained by Miller’s indices (hkl) . We can determine Miller’s indices by a few steps as the following:

1. Choose the original point.

0

𝒙

𝒚

𝒛

2. Assume a plane crosses these axis at on , on and on .

𝒑𝒂

𝒒𝒃𝒓𝒄

3. Take the reciprocal of the numbers( and )

3. Reduce to the integers having the same ratio, usually the smallest three integers. The result, enclosed in parentheses (), is called the index of the plane.


𝒙𝒚

𝒛Example:

1

1

1𝑥𝑦𝑧𝑖𝑛𝑡 .∞1∞𝑟𝑒𝑝 . 10 11 10h𝑘𝑙010

010

In same method, we can find the other face planes

0

001

100

(): explain how you can find the hkl of the specified planes (a=1) in below figures.

𝑥

𝑦

𝑧

𝑥

𝑦

𝑧

𝑥

𝑦

𝑧

𝑥

𝑦

𝑧

𝑥

𝑦

𝑧12

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One important characteristic in semiconductor crystals is the surface concentration of atoms on the surface , number per square centimeter (atom/cm2), that are cut by a particular plane. This characteristic is called “ The surface density of atoms “ .Again, a single-crystal semiconductor is not infinitely large and must terminate at some surface.

To calculate the surface density of atoms on a particular plane in a crystal.

Consider the body-centered cubic structure and the (110) plane . Assume the atoms can be represented as hard spheres with the closest atoms touching each other. Assume the lattice constant is a = 5 Å 𝒂

𝒃

𝒄 110

a

a

5 Å

5 Å

A

B

C

𝐴𝐵=√𝐵𝐶2+𝐶𝐴2

¿√𝑎2+𝑎2¿√2𝑎2

Å

𝑻𝒉𝒆 𝒔𝒖𝒓𝒇𝒂𝒄𝒆𝒅𝒆𝒏𝒔𝒊𝒕𝒚=𝑵𝒐 .𝒐𝒇 𝑨𝒕𝒐𝒎𝑨𝒓𝒆𝒂𝒐𝒇 𝒑𝒍𝒂𝒏𝒆

¿𝟐(𝒂𝒕𝒐𝒎)

𝟓×𝟓√𝟐 ( Å )¿

𝟐(𝒂𝒕𝒐𝒎)(𝟓×𝟏𝟎−𝟖)𝟐 .√𝟐 (𝑐𝑚)2

5.66 Atoms /

(): E1.4 in Semiconductor Physics and Devices(Donald A. Neamen) p.9


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13.4 :The Diamond Structure

Silicon is the most common semiconductor material. Silicon is referred to as a group IV element and has a diamond crystal structure. Germanium is also a group IV element and has the same diamond structure.

A unit cell of the diamond structure.

The diamond structure refers to the particular lattice in which all atoms are of the same species, such as silicon or germanium. The zincblende (sphalerite) structure differs from the diamond structure only in that there are two different types of atoms in the lattice

A unit cell of the zincblende structure. (): E1.5 in Semiconductor Physics and Devices(Donald A. Neamen) p.11


http://upload.wikimedia.org/wikipedia/commons/2/22/Diamond_Cubic-F_lattice_animation.gif

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1.4 :ATOMIC BONDING

Atomic Bonding Types : 1. Ionic bonding .2. Covalent bonding .3. Co-ordinate ( dative covalent ) bonding.4. Electronegativity.5. Shaes of simple molecules and ions .6. Metallic bonding .7. Van der waals forces.8. Hydrogen bonding 9. Bonding in organic compounds .

Covalent bonding

If we’ve two atoms , that are IV valency

Si SiSi

Si SiSi

Si SiSi

Si SiSi

Si SiSi

Si SiSi


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1.5 : GROWTH OF SEMICONDUCTOR MATERIALS

• Czochralski’s method . جوكرلسكي طريقة In this technique, a small piece of single-crystal material, known as a seed , is brought into contact with the surface of the same material in liquid phase, and then slowly pulled from the melt. As the seed is slowly pulled, solidification occurs along the plane between the solid-liquid interface.


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Epitaxial Growth

The word epitaxy is derived from the Greek “epi”— upon, and “taxis”— to arrange.Thus, epitaxial silicon deposition requires the ability to add and arrange silicon atoms upon a single crystal surface. Epitaxy is the regularly oriented growth of one crystalline substance upon another.

Two different kinds of epitaxy are recognized:• Homoepitaxy growth in which the epitaxial

layer is of the same material as the substrate.• Heteroepitaxy growth in which the epitaxial

layer is a different material from the substrate.


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CVD (Chemical Vaporation deposition is a heterogeneous reaction involving at least the following steps:

1. Bulk transport of reactants into the process volume2. Gaseous diffusion of reactants to the surface3. Absorption of reactants onto the surface

Removal of reactant by-products1. Reaction by-product desorption ( المج , تزازاالم ) 2. Gaseous transport of by - products3. Bulk transport of by-products out of process volume

Surface reaction1. Surface reaction (reaction can also take place in the gas volume immediately above the surface)2. Surface diffusion3. Crystal lattice incorporation


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Semiconductors ch. 1