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Figure (1.55) in SSPD_Chapter 1_Part 11_Soild state of Matter_Crystalline Nature of Solid depicts the three cubic crystal systems: simple, bcc and fcc.

Silicon and Germanium are Diamond lattice structures. Diamond structure has been described in SSPD_Chapter 1_Part 11_Soild state of Matter_Crystalline Nature of Solid in Figure 56.

  • Diamond lattice structure belongs to cubic- crystal family.
  • Diamond structure is two interpenetrating fcc sub-lattices with one sub-lattice displaced with respect to the other along the diagonal of the cube by one quarter of the diagonal length i.e. by a√3/4 as shown in Figure(1.56.A).
  • We can better visualize the diamond structure by dividing one major cube (a×a×a) into 8 sub- cubes (a/2×a/2×a/2) by the name A,B,C,D in the upper half of the major cell and E,F,G,H in the lower half of the major cell as shown in Figure(1.56.B). Subcell E is hidden from sight.
  • The perspective view of the major cell is shown in Figure (1.56.B)
  • The plan view is shown in Figure (1.56.C) .
  • Each major cell has 4 subcells A,C,F,H containing tetrahedral structures of silicon or germanium atoms.
  • A tetrahedral structure is shown in Figure(1.56.D). A tetrahedral structure lies in a subcube.
  • There is one atom at the center of the subcube.
  • This body center atom time-shares its 4 valence electrons with 4 valence electrons of the corner atoms of the subcube.
  • The 4 corner atoms forming the covalent bonds with the body centered atom are the two diagonally opposite corner atoms on the upper plane and two diagonally opposite corner atoms on the lower plane but this time it is the other diagonal.
  • That is the two sets of diagonally opposite corner atoms comprise two orthogonal diagonals.
  • Thus in plan view we see, as in Figure (1.56.C), each Si(or Ge) time sharing its 4 valence electrons with 4 valence electrons of the four corner neighboring atoms and in the process each central atom is fulfilling its octave condition.
  • This is 100% covalent bond as the center of positive charge and the center of negative charge are coincident.
  • Each atom in the bulk is sharing the 4 valence electrons with 4 neighboring corner atoms hence octave condition and thereby covalent bond is fulfilled every where except at the surface of the crystal.
  • Hence at the surface we have unfulfilled covalent bonds or dangling bonds.

These dangling bonds are responsible for the surface states which if not properly controlled and passivated will lead to serious flicker noise problem as well as to the failure of the devices. At the initial stages of MOS fabrication there was serious Na impurity problem coupled with surface states problem which was leading to very low yields. Andy Grove, who was the cofounder of INTEL along with Gordon Moore and Robert Noyce , came into grip of this problem and gave a permanent solution of the low yields which enabled MOS Technology to take off. MOS Technology is the key to the fabrication of microprocessors.

GaAs has zincblende lattice which is identical to diamond lattice except that one fcc sublattice consists of Ga and the other fcc sublattice consists of As. So in Plan View we see Ga atom surounded by four As atoms and similarly As atom is surrounded by four Ga atoms thereby each atom is fulfilling the octave condition by time sharing the electrons from the 4 neighboring atoms. The plan view of GaAs tetrahedral structure is shown in Figure(1.61).

Figure 1.61. Zincblende structure of GaAs.

1.11.7. CRYSTAL ORIENTATION.

Crystals are anisotropic because of different pattern of arrangement of atoms in different directions. Hence etching rate of the crystal is different in different directions. This property is utilized in Integrated Circuit Technology. Therefore crystal orientation is important in device fabrication and hence needs to be clearly defined.

The basis in which we define the planes and directions of a crystalline lattice is made possible by Miller Indices. This is derived from the Cartesian Coordinates in the following manner:

  1. Any atom in the crystalline lattice is taken as the origin;
  2. Reference coordinate axes are set up in the direction of basis vectors;
  3. Consider a system of parallel planes. Find the intercepts made by one of the planes. Express them as multiples of unit basis vectors;
  4. Take their reciprocals and reduce them to the smallest triad of integers h,k and l having the same ratio.(hkl) is the Miller Index of that system of parallel planes and<hkl>is the direction normal to the plane;
  5. Suppose a plane has intercepts 2a, 3b and 4c where a, b and c are unit basis vectors along X, Y and Z axes. Then reciprocal is (1/2,1/3,1/4). These reciprocals are reduced to the smallest triad having the same ratio. The Miller index is (6,4,3). This has been obtained by multiplying the reciprocals with lowest common multiple of the denominator terms. The denominator terms are 2,3,4. The LCM is 12. Miller Index has been obtained by multiplying the reciprocals by 12.
  6. (6,4,3) is the Miller Index of the given plane and<6,4,3>is the orientation vector of the plane.

The normal to the plane along which the crystals cleave is the crystal cleavage plane.. Generally they cleave along<1,1,1>plane. The cleavage plane is the plane of highest atomic density. If the surface of the Si wafer, known as major flat, is parallel to<111>plane then the crystal orientation is<111>. Different planes of a crystal structure is shown in Figure (1.62).

If the surface of the wafer is parallel to YZ plane then the crystal orientation is<100>. For MOS fabrication crystals with orientation<100>is utilized. For other applications<111>crystal orientations are preferred.

Figure. 1.62. Different Planes of a crystal.

Questions & Answers

How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
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
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
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.
Bharti
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
Daniel
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
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
How can I make nanorobot?
Lily
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
NANO
how can I make nanorobot?
Lily
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
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.
Tarell
what is the actual application of fullerenes nowadays?
Damian
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.
Tarell
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.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
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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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