<< Chapter < Page Chapter >> Page >

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 we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
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
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
How can I make nanorobot?
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
how can I make nanorobot?
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!

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
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Solid state physics and devices-the harbinger of third wave of civilization' conversation and receive update notifications?