Silicon

From SiO_2,silicon is obtained via a chemical process (carboreduction) that takes place at T > 1925 K (Si melting T)

SiO₂ + 2C—› Si + 2CO

Silicon so obtained is not pure and HCl is added to“wash” it; then, introducing H₂, a catalytic deposition is performed passing through a trichlorosilane intermediate. The physical process of silicon purification is called zone melting or zone refining; this process is based on the fact that impurities contained in silicon have a melting point temperature that is lower than Si, and in this way, it is easy to remove them.

The main feature of silicon is its semiconductor behavior, i.e. its resistivity is between that of metals and dielectrics. Differently from metals, Si (and similarly the other semiconductors) has an energy bandgap between the highest occupied electronic level (also VB, Valence Band) and the lowest unoccupied one (CB, Conduction Band). The reported experimental value is Eg ~ 1.1 eV at 298 K.

Adding small amounts of different atoms can improve the conductive properties of silicon. Indeed the presence of trivalent (B, Al, Ga) or pentavalent (P, As) atoms (p and n doping, respectively), formally corresponds to have an extra positive charge or an extra negative charge. The increased number of carriers thus improves the conductivity of silicon.

Interface of silicon with its own oxide, Si-SiO₂, plays an important role in electronic devices and it can be engineered with a very high precision. The figure below shows the chemical bonding at the Si-SiO₂ interface with the different orientation of crystalline silicon surface, (100), (110) and (111).

The relatively low cost and these unique properties make Silicon the main component of modern technological devices, such as transistors, and integrated circuits, in particular, CMOS

Even primarily employed in electronics, Silicon plays a fundamental role as constituent of other classes of compounds:

Silicone (polymerized siloxanes with the common formula [R2SiO]n; R = CH3, C2H5 or C6H5) and Polysilsesquioxanes are both hybrids of organic/inorganic materials that have wide applications. The organic group is bound to Si via a Si-C bond, and the size and the properties of this organic group highly influence the overall properties of these polymeric materials in terms of porosity, thermal stability and other properties.

Silicon not Silicone	Polysilsesquioxanes

More information on Silicon and its properties is available at the following web sites:

History
The history of Silicon
The history of silicon Valley
http://periodic.lanl.gov/elements/14.html
http://nautilus.fis.uc.pt/st2.5/scenes-e/elem/e01400.html
The history of the integrated circuit

Crystal Lattice–Structures
Silicon crystal structure
http://cst-www.nrl.navy.mil/lattice/
http://database.iem.ac.ru/mincryst/

Si–SiO₂ Interface
From Semiconductor Glossary
Phys. Rev. B 24, 4593 – 4603 (1981)
Amorphous silicon–SiO₂ interface
Thermal oxidation of silicon
Computational design of Si/SiO₂ interfaces: Stress and strain on the atomic scale
Oxygen Diffusion through the Disordered Oxide Network during Silicon Oxidation
Microscopic structure of the SiO₂/Si interface

Integrated circuits & Electronic Devices
The transistor in a century of electronics
MOS Capacitors
Integrated circuit
How is an integrated circuit made?
Nobel prize in physics 2000
First transparent integrated circuit

CMOS
The future of CMOS technology
CMOS technology platform
Advanced CMOS
CMOS, the ideal logic family
CMOS processing technology
Integrated CMOS technology
CMOS Sensor Technologies

Zeolites
Database of zeolite structures
The zeolite group of minerals
What are zeolites?
Determination of crystal structures by Monte Carlo methods
From Abey newsletter
The MCS zeolite page
You can thank NASA astronauts

Polysilsesquioxanes
Hybrid organic–inorganic materials
Hybrid organic–inorganic membranes
Bridged polysilsesquioxanes

This web page is prepared by Dr. Giacomo Giorgi from the University of Perugia, Italy. Photos by Natalie and Dwight Hanson