ByShadia M.S.Elayyat

Objective Review Type of materials Type of semiconductor P-N junction Thin film DefinitionType Thin film deposition ApplicationReferences

ObjectivesThe main objectives of this research are-:

Study the characteristics of the materialsStudy P-N junction Discus and study the thin film depositionStudy the application and uses of thin film

Materials

Conductor

Semiconducto

r

Insulator

plastics, paper, glass 

 gold, silver, nickel, iron .

Silicon , Germanium

Conductor mostly metalshave the highest conductivities

The conductivity decrease

as the temperature increase

Insulator • have high resistivity• does not conduct an electric current under the influence of an electric field

•Example :PlasticsPaper glass 

semiconductor

Semiconductors are materials whose electrical properties lie between Conductors and Insulators.

Some common semiconductorselemental Si - Silicon (most common) Ge - Germaniumcompound GaAs - Gallium arsenide GaP - Gallium phosphide AlAs - Aluminum arsenide AlP - Aluminum phosphide InP - Indium Phosphide

The resistivity of the semiconductor materials decrease as the temperature increase as shown if the figure

Valance BandThe outermost orbital of an atom, where electrons are so tightly bounded that, they can not be removed as free electron

Conduction BandThis is the highest energy level or orbital in outer most shell, in which electrons arefree enough to move.Band GapThere is one energy gap separates these two bands, - the valance band and conduction band. This gap is called forbidden energy gap

Metal very small energy gab

Semiconductor moderate E.GInsulator Large energy gab

The electrical conductivity at room temperature is quite different for each of these three kinds of materials Metals have the highest conductivities followed by semiconductorsand then by insulators

insulators

Two type of semiconductor

Intrinsic( undoped ) semiconductor: the number of excited electrons and the number of holes are equal: n = p

Type of semicondu

ctor

Extrinsic semiconductor : is a semiconductor that has been doped.

Doping involves adding dopant atoms to an intrinsic semiconductor, which changes the electron and hole carrier concentrations of the semiconductor at thermal equilibrium.

an extrinsic semiconductor classify it as either an n-type or p-type semiconductor

(Ge)

+3 +4 +5

Group III Group IV Group V

Boron (B) Carbon (C) Nitrogen (N)

Aluminium (Al) Silicon (Si) Phosphorus (P)

Gallium (Ga) Germanium Arsenic (As)

Indium (In) Tin (Sn) Antimony (Sb)

Semiconductor Elements in the Periodic Table

P-type semiconductor is an intrinsic semiconductor in which an impurity acting as an acceptor(number of holes grater than number of electrons )N-type semiconductor is an intrinsic semiconductor in which a donor impurity has been intentionally introduced(number of electrons much grater than holes).

Lattice structure of p-type semiconductor

• The impurity could be indium or gallium, both of which have only three valence electrons.•Majority carriers are holes •Minority carriers areelectrons

Lattice structure of N-type semiconductor

•The impurity could be arsenic ,which have only five valence electrons.•Majority carriers are electrons •Minority carriers areholes

P-N Junction A p–n junction is a boundary or interface between two types of semiconductor material, P-type and N-type .

p–n junctions are building blocks of most semiconductor electronic devices such as diodes, transistors, solar cells, LEDs.

When the p-type and n-type semiconductors are join , electrons from the n region near the p–n interface diffuse to the p-type region. As electrons diffuse, they leave positively charged ions ,in the n region. The holes from the p-type region near the p–n interface diffuse to the n-type region, leaving fixed ions with negative charge. The regions nearby the p–n interfaces lose their neutrality , forming the depletion zone.

Forward bias the p-type is connected with the

positive terminal and the n-type is connected with the negative terminal

 the holes in the P-type region and the electrons in the N-type region are pushed toward the junction. This reduces the width of the depletion zone.

Reverse biasthe p-type is connected with

the negative terminal and the n-type is connected with the positive terminal

the voltage at the cathode is higher than that at the anode. So, no current will flow 

the holes in the P-type material are pulled away from the junction, causing the width of the depletion zone to increase. Likewise, the electrons in the n-type material will also be pulled away from the junction.

The reverse

saturation current

Threshold voltage

Break down voltag

e

What is a "thin film? "

thin = less than about one micron ( 10,000 Angstroms, 1000 nm)

film = crystalline or amorphous layer of material on a substrate

Thin films are crystalline or amorphous layers, typically 1 nm – 10 µm thick, deposited on a substrate.

Classification of Thin Films

single crystalsPolycrystallineamorphous

Properties of Thin Films

not fully denseunder stressquasi - two dimensional (very thin films)

glass

Substrate(transparent conducting oxide )

Thin film

thin film deposition

Chemical Vapor DepositionPhysical Vapor DepositionElectrodepositionLangmuir-Blodgett

Chemical Vapor Deposition

• process used to produce high-purity, high-performance solid materials

• Reactive gases interact with substrate

• Used to deposit Si and dielectrics

Type of CVD• Atmospheric pressure – APCVD• Low pressure – LPCVD• Plasma enhanced – PECVD• High density plasma - HDPCVD

Chemical Vapor Deposition

Involves one or more gas phase species which react on a solid surface (substrate) to deposit a solid film.

the reaction is initiated by heating the substrate. Other mechanisms of supplying the activation energy necessary to initiate reactions include: laser CVD, photo CVD, and plasma enhanced CVD.

Physical Vapor Deposition

There are two type of PVD :-evaporation Sputtering• Very few chemical reactions• deposits almost any material• Always performed in vacuum.• Vacuum increases mean free path of

ions or atoms• Vacuum is typically less than 10–4 Torr

A thermal evaporator uses an electric resistance heater to melt the material and raise its vapor pressure to a useful range. This is done in a high vacuum, both to allow the vapor to reach the substrate without reacting with or scattering against other gas-phase atoms in the chamber, and reduce the incorporation of impurities from the residual gas in the vacuum chamber.

Sputtering (sputtering mean a process which atoms are ejected from a solid target material due to bombardment of the target by energetic particles).This way is one of the most flexible deposition techniques. It is especially useful for compounds or mixtures, where different components would otherwise tend to evaporate at different rates. Uses a plasma (usually a noble gas, such as argon) to knock material from a "target" a few atoms at a time. The target can be kept at a relatively low temperature, since the process is not one of evaporation. Sputtering widely used in the optical media. The manufacturing of all formats of CD, DVD, and BD are basically done with the help of this technique. It is a fast technique and also it provides a good thickness control

Applicationsmicroelectronics - electrical

conductors, electrical barriers, diffusion barriers .

magnetic sensors -gas sensorsoptics - anti-reflection coatingssolar cell fabricationphotodiodesswitching devices

Uses microelectronic devicestelecommunication deviceswear resistant coatingsoptical coatings (windows,solar cells)Sensorscatalysts

Reference

Karl W. Böer, “Survey of Semiconductor Physics Volume II: Barriers, Junctions, Surfaces, and Devices”, Springer,617-619 (1992).

Always Learning, “Electronic Devices and Circuits”, Pearson Education India,26-27 (2008).

Preeti Maheshwari, “Electronic Components and Processes”, New Age International,25( 2006).

R.S.Sedha, “A Textbook of Electronic Circuits”, S. Chand, 32-45(2008).

S. Mani Naidu, Naidu S. Mani,” Applied Physics”, Pearson Education India,38-45( 2009).

Simone Raoux, Matthias Wuttig, “Phase Change Materials: Science and Applications”, Springer, 102(2010).

Masanori Okuyama, Yoshihiro Ishibashi, “Ferroelectric Thin Films: Basic Properties and Device Physics for Memory Applications”, Springer, (2005).

Y.Paulean,“Chemical Physics of Thin Film Deposition Processes for Micro- And Nano-Technologies”, Springer,vii-4( 2002).

any solid object in which an orderly three-dimensional arrangement of the atoms, ions, or molecules is repeated throughout the entire volume

Single crystal

materials are solids that are composed of many crystallites of varying size and orientation. The variation in direction can be random (called random texture) or directed.all common metals and many ceramics are polycrystalline

Polycrystalline

 non-crystalline solid is a solid that lacks the long-range order characteristic of a crystal.

amorphous