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Our main interest is Si, Ge , GaAs and other compound semiconductors used in Photonics. The portion of Periodic Table related to Solid State Technology including Photonics is shown in Table(1.23).

Table.1.23. Portion of the Periodic Table related to Semiconductors&Photonics.

Period Column II Column III Column IV Column V Column VI
2 B C N
3 Mg Al Si P S
4 Zn Ga Ge As Se
5 Cd In Sn Sb Te
6 Hg Pb

1.11.3. POLYCRYSTAL&AMORPHOUS.(Refer Figure 1.39, Chapter1_Part 10_Electron in single crystal and band theory of solid)

Single Crystals exhibit long range periodicity. Single Crystal Silicon Atoms are 4-fold coordinated in exactly the same manner as Diamond crystal. This 4-fold coordination exists throughout the 3D crystalline lattice except at the surface. At the surface there are incomplete bonds which are known as dangling bonds and which give rise to surface states. These surface states introduce traps or recombination centers. These surface states reduce lifetime and reduce mobility of the carriers. The random capture-release of carriers from the conducting channel of MOS devices by these surface states give rise to flicker noise. By Silicon Dioxide passivation layer, these surface states can be inactivated and the adverse effects are minimized.

Silicon Polycrystals exhibit short range periodicity of the order of micrometers. These are grain sizes. These grains or crystal domains are divided by domain/grain boundaries. Grain boundaries are 2D surfaces where 2D defects are present. Defects are present due to broken bonds or due to incomplete bonds. Each domain has its own direction of periodicity and the direction of the periodicity changes from domain to domain. The basic unit cell remains the same in all domains.

Amorphous silicon has a still shorter range of periodicity or no periodicity. This is an irregular structure and has ill defined energy band gap. Because of irregularities there are a large number of dangling bonds within the bulk of the crystal as shown in Figure (1.35). These dangling bonds introduce traps within the bulk of a-Si (amorphous silicon) and hence severely reduce the lifetime as well as mobility of the mobile carriers. While depositing a-Si if hydrogen (or fluorine) introduced then H-atoms “tie –up” the dangling bonds and these improves the electrical properties of a-Si. Hydrogenated a-Si is denoted as a-Si:H.

The technology of growing amorphous silicon is much cheaper than the technology of growing single crystal silicon therefore amorphous silicon solar voltaic cells are emerging as a more economically viable option as renewable energy resource.

Poly-crystal silicon has an unique position in MOS fabrication. MOS stands for Metal-Oxide-Semiconductor. The use of heavily doped poly-silicon layer in place of aluminum as the metal electrode in MOS has proved to be far superior. This is especially true for thinner gate oxides of the order of 100 to 200 A°.

Doped poly-silicon is also used as diffusion source for creating shallow junctions.

Heavily doped Poly-silicon layer on N-Type silicon crystal gives an ohmic contact. By the conventional route of metallization, if we deposit aluminum layer on N Type crystal we obtain a rectifying contact. To ensure an ohmic contact to N type silicon crystal, we have to go for N + contact deposition in N type silicon and then depositing an aluminum contact layer. This ensures ohmic contact but it entails an extra deposition. Deposition of heavily doped poly-silicon directly on N type silicon crystal gives ohmic contact. This simplifies the fabrication steps.

Using doped poly-silicon, interconnections can be made. Variously doped poly-silicon can be used to fabricate high value IC resistors.

The range of orderliness in single crystal, poly-crystal and amorphous is depicted in Figure (1.39).

Table (1.24) tabulates the properties of crystalline and amorphous silicon.

Table 1.24. Crystalline and amorphous silicon.

[From Principles of Electronic Materials and Devices, Second Edition, S. O. Kasap(© McGraw- Hill, 2002)]

Crystalline Sic-Si Amorphous Sia-Si Hydrogenated a-Sia- Si:H
Stucture Diamond cubic Short range order only.Contains micro-voids and dangling bonds. Short range order only.Structure contains typically 10% H.Hydrogen atoms passivate dangling bonds and relieve strain from bonds.
Preparation method Czochralski technique/Float zone technique/epitaxial growth(CVD or Liquid Phase Epitaxy) Electron beam evaporation of Si. Chemical vapor deposition(CVD) of silane gas by RF induction heating.
Density (gm/cm 3 ) 2.33 3 to 10% less dense 1 to 3% less dense.
Electronic applications Discrete and integrated electronic devices. None Solar cells,Thin Film Transistor Arrays in Flat Panel Displays.Photoconductor drums used in photocopying.

Questions & Answers

how can chip be made from sand
Eke Reply
are nano particles real
Missy Reply
Hello, if I study Physics teacher in bachelor, can I study Nanotechnology in master?
Lale Reply
no can't
where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
has a lot of application modern world
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
Nasa has use it in the 60's, copper as water purification in the moon travel.
nanocopper obvius
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
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Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
analytical skills graphene is prepared to kill any type viruses .
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
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Source:  OpenStax, Solid state physics and devices-the harbinger of third wave of civilization. OpenStax CNX. Sep 15, 2014 Download for free at http://legacy.cnx.org/content/col11170/1.89
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