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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

what is math number
Tric Reply
x-2y+3z=-3 2x-y+z=7 -x+3y-z=6
Sidiki Reply
Need help solving this problem (2/7)^-2
Simone Reply
x+2y-z=7
Sidiki
what is the coefficient of -4×
Mehri Reply
-1
Shedrak
the operation * is x * y =x + y/ 1+(x × y) show if the operation is commutative if x × y is not equal to -1
Alfred Reply
An investment account was opened with an initial deposit of $9,600 and earns 7.4% interest, compounded continuously. How much will the account be worth after 15 years?
Kala Reply
lim x to infinity e^1-e^-1/log(1+x)
given eccentricity and a point find the equiation
Moses Reply
12, 17, 22.... 25th term
Alexandra Reply
12, 17, 22.... 25th term
Akash
College algebra is really hard?
Shirleen Reply
Absolutely, for me. My problems with math started in First grade...involving a nun Sister Anastasia, bad vision, talking & getting expelled from Catholic school. When it comes to math I just can't focus and all I can hear is our family silverware banging and clanging on the pink Formica table.
Carole
I'm 13 and I understand it great
AJ
I am 1 year old but I can do it! 1+1=2 proof very hard for me though.
Atone
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Adu
Not really they are just easy concepts which can be understood if you have great basics. I am 14 I understood them easily.
Vedant
find the 15th term of the geometric sequince whose first is 18 and last term of 387
Jerwin Reply
I know this work
salma
The given of f(x=x-2. then what is the value of this f(3) 5f(x+1)
virgelyn Reply
hmm well what is the answer
Abhi
If f(x) = x-2 then, f(3) when 5f(x+1) 5((3-2)+1) 5(1+1) 5(2) 10
Augustine
how do they get the third part x = (32)5/4
kinnecy Reply
make 5/4 into a mixed number, make that a decimal, and then multiply 32 by the decimal 5/4 turns out to be
AJ
how
Sheref
can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
ninjadapaul
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
ninjadapaul
I don't understand what the A with approx sign and the boxed x mean
ninjadapaul
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
ninjadapaul
oops. ignore that.
ninjadapaul
so you not have an equal sign anywhere in the original equation?
ninjadapaul
hmm
Abhi
is it a question of log
Abhi
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salma
Commplementary angles
Idrissa Reply
hello
Sherica
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Sherica
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Tamia
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Uday
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salma
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opoku
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greetings from Iran
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Nharnhar
A soccer field is a rectangle 130 meters wide and 110 meters long. The coach asks players to run from one corner to the other corner diagonally across. What is that distance, to the nearest tenths place.
Kimberly Reply
Jeannette has $5 and $10 bills in her wallet. The number of fives is three more than six times the number of tens. Let t represent the number of tens. Write an expression for the number of fives.
August Reply
What is the expressiin for seven less than four times the number of nickels
Leonardo Reply
How do i figure this problem out.
how do you translate this in Algebraic Expressions
linda Reply
why surface tension is zero at critical temperature
Shanjida
I think if critical temperature denote high temperature then a liquid stats boils that time the water stats to evaporate so some moles of h2o to up and due to high temp the bonding break they have low density so it can be a reason
s.
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
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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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