Chapter 1. The Crystal Structure of Solids

1
Chapter 1. The Crystal Structure of Solids
Semiconductor Materials Type of Solids Space
Lattices Atomic Bonding Imperfections and
Impurities in Solids Growth of Semiconductor
Materials
Young-Hwan Lee http//cafe.daum.net/lyh201circuit
E-mail lyh201_at_hanyang.ac.kr Mobile
010-7178-1884
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1.1 Semiconductor Materials

• Bell Telephone Lab.(U.S.A)? Shockley, Bardeen,
  Brattain? ??(1956? Nobel ???? ????) 1948? ??? Ge
  single crystal? ??? point contact Transistor?
  ??.
• semiconductor material ? ?? ? ????? ???? ??? ???
  semiconductor devices? ???? ??? ??? ??.

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1.1 Semiconductor Materials

• Semiconductors are a group of materials having
  conductivities between those of conductors and
  insulators.
• General classification
• - elemental semiconductor group IV of the
  periodic table
• (A semiconductor composed of a single
  species of atom)
• - compound semiconductor special
  combination of group III and group V elements
  (binary compound, ternary compound)

III IV V
B C
Al Si P
Ga Ge As
In Sb
Compound semiconductors Compound semiconductors
AlP Aluminum phosphide
AlAs Aluminum arsenide
GaP Gallium phosphide
GaAs Gallium arsenide
InP Indium phosphide
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1.1 Semiconductor Materials

• semiconductor materials? ??
• (1) electrical resistivity ?? 10-6 106 ?
  m ? ??
• ??? ????
  ??? ??.
• (2) energy band structure?? energy gap(Eg)? 1
  eV??.
• (3) electrical resistivity? temp. coefficient
  negative
• ? semiconductor insulator ()
  conductor ()
• electrical resistivity? temp. ??? ?? ??.
  ? electrical conductivity? temp.??? ?? ??? ????
  ??? ??.
• (4) semiconductor? ???? impurity? ??? ?? ??
  conductivity? ??? ??.
• (5) ambipolar conduction
• ? carriers electron hole
• (6) rectifying action, photoelectric effect,
  Hall effect, thermo-electric effect etc. ??? ??

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1.1 Semiconductor Materials

• semiconductor materials
• (1) elemental semiconductor
• (2) compound semiconductor
• (a) intermetallic compound semiconductor
• (b) oxide semiconductor
• (3) organic semiconductor
• (4) amorphous semiconductor

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1.1 Semiconductor Materials

• 1. elemental semiconductor (group IV elements)
• (1) Ge diamond structure (atomic number
  32)
• 
  at 300 K
• 
  at 300 K
• ? 70? ???? intrinsic conduction? ????
  device? ???? ??? ??(melting point 960?).
• (2) Si diamond structure (atomic number
  14)
• 
  at 300K
• 
  at 300K
• ? O2 ???? ???? ?? ???? ???? ??? ??? ???
  ???? ?? (melting point 1,410?).

2. compound semiconductor 2????? ??? ???? ??
inorganic semiconductor? ???. ????? (1) ???
??? ??? ??? (2) single
crystal ??? ?? ??? ???? ??.
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1.1 Semiconductor Materials

• (1) intermatallic compound semiconductor
• A. binary compound semi.
• III? elements(B, Al, Ga, In)? V?
  elements(N, P, As, Sb) ? mole?? ???? ??
  zincblende structure? compound.
• IV? elemental semiconductor? ?? higher
  electron mobility ? high frequency transistor
• GaAs
  at 300K
• Si
  at 300K
• larger energy gap ? high temp. devices
• GaAs (Eg 1.43 eV) at
  300 K
• Si (Eg 1.12 eV)
  at 300 K

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1.1 Semiconductor Materials

• B. ternary compounds GaAs-AlAs AlxGa1-xAs
• GaP-InP
  GaxIn1-xP
• 
  GaAs-InAs GaxIn1-xAs
• 
  AlAs-InAs AlxIn1-xAs etc.
• ? mixed crystal? ???? ?? energy gap? ????
  ????? ???? ? ???? optoelectronics materials? ??.
• ? GaAs (Eg 1.43 eV) AlAs(Eg 2.13 eV)?
  mixed crystal? AlxGa1-xAs(x? Al???)?? x? ??(01)?
  ??
• a) Eg? ???? ??
• b) ??? GaAs??? AlAs? ???? ??
• c) GaAs(5.6533Å at 300K)? AlAs(5.6605Å at
  300K)? lattice const.? ?? ???? GaAs?? ?? AlAs?
  ???? hetero structure? ??? ????? ?? ??.
• ? HBT(heterojunction bipolar transistor,
  cf. BJT),
• MODFET(modulation-doped field effect
  transistor multilayer modulation-doped
  heterostructure) ?? ?? .

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1.1 Semiconductor Materials

• (2) oxide semiconductor
• ????? metal? oxide? Eg? ?? insulator? ????
• ???? ??? ?? ???? ?? ??? ??.
• p-type semiconductor Cu2O, NiO, CoO, FeO,
  Cr2O3,
• 
  Bi2O3, MoO3, Ti2O3
• n-type semiconductor ZnO, CdO, TiO2,
  Al2O3, ThO2, SnO2 etc.
• Cu2O ? metal?? ???? ???? ?? ???? ???? ??.
  ??? Si???? ???? ?? ??? ??.
• ZnO ? varistor material
• SnO2 ? thin film?? ??? ????, ???? ???? ????
  ?? ?? ??? ????, EL?? ??, ??????? ?? ?? ?? ??? ??
  ??? ?? ?????? ??.

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1.1 Semiconductor Materials
(3) organic semiconductor

• ???? ???? ???? ?? ???, ????? ?? ????? C-H ???
  semiconductor
• ????? organic compound? ???? ?? ??? ?? ?? ?????
  large potential barrier? ????? electron? ????? ??
  ?? ??? ?? ??? ??, ???? ??? ? ?? electron(p
  electron in anthracene C14H10)? ?? ?? ?? ??
  ???? ??? ???? organic compound? ??, ??? ?? ??
  ???? ??? ?? ??? ??? ????.
• ? p electron ? ???? ??? ?? free electron? ???
  ??? ??? ???? ?? ?? ????? ??.

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1.1 Semiconductor Materials

• (4) amorphous semiconductor
• ????? ???? ?? ??? long range order? ???
  ??? ??? ??? ??? ????? ?? ???? ??(short range
  order) ??? ??? semiconductor
• a. elctron? ?????? s p??? 8?? ??? ?? ????
• b. a-Ge, a -Si??? ??? ????? sp????? ?? ????
  ??? ??.
• c. ????? ???? ???? ???? forbidden band?? ????
  localized energy level? ??
• ? low carrier mobility ( for a-Ge a-Si)
• d. a-Si? solar cell, TFT(thin film tr.) ?? ??.
• ??? ? memory device??? ???.
• e. Se, Te etc.(chalcogen element) ? amorphous
  semiconductor (chalcogenide glass)
• ? ?????? ????? ??.

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1.2 Types of Solids

• SOLDIS ? ???? ?????? atoms? ??? ????? ?? three
  different types? ??.

(1) single crystal (crystalline) atom or atom
group? regular arrangement ltatomic
arrangement? regular geometric periodicity? ??.
(atom? long-range order? ??)gt

• semiconductor devices? ????? single crystal
  materials? ??.
• single-crystal materials? growth? semiconductor
  technology?? ??.
• electrical properties? nonsingle-crystal
  material? ?? ??.

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1.2 Types of Solids
(2) polycrystalline atom or atom group? ????
regular arrangement ltgrain boundary? ?? ????
many small crystals? ??gt ?poly-Si? MOS
devices?? gate materials? ??.
(3) amorphous atom or atom group? irregular
arrangement ltshort-range ordergt ?solar cell,
TFT ??? a-Si? ???.
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1.3 Space Lattices

• single-crystal?? ????? regular geometric
  periodicity.
• ? ??? atom or atom group? 3??? ? ???? ??? ????
  ??.
• lattice The periodic arrangement of atom in a
  crystal.
• lattice point a particular atomic array by a
  dot.
• 1.3.1 Primitive and unit cell
• ?? ???? ????? atom? ????? ??? atom? ??.
• " translational symmetry,
  ???? "
• ? ???? three fundamental vectors? ??? ? ??.
• 
  (1-1)
• where p, q, s are arbitrary
  integers
• ?? ? eq.(1-1)? ?? ???? points
  lattice point
• eq.(1-1)? ?? ???? lattice points? ?? space
  lattice
• vector a, b, c? ?? ???? ??6?? primitive
  cell or unit cell
• ? primitive cell ?? 6??? eight corners??
  lattice points? ??.
• unit cell ?? 6??? eight corners?? ???
  face-center or volume center?? lattice point ??.

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1.3 Space Lattices

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1.3 Space Lattices

• 1.3.2 Basic Crystal Structures
• single-crystal atom? 3-dimensional periodical
  array.
• ? this periodical array? lattice sites? ????
  three independent shortest vectors? primitive
  basis vectors (a, b, c)? ?? define?.
• where p, q, s are
  arbitrary integers
• primitive vectors(a, b, c)? ? vector?? ? a, ß,
  ?? ?? ???? ??6??. " primitive cell
• ? a, b, c, a, ß, ? lattice constants

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1.3 Space Lattices
FCC (face-centered cubic) 8 corner atoms6 f-c
atoms of atoms/unit cell 8 (1/8) 61/2
4 Ag, Al, Au, Ca, Cu, Ni, Pd, Pt, Rh
SC (simple cubic) 8 corner atoms of
atoms/unit cell 8 (1/8) 1
BCC (body-centeredcubic) 8 corner atoms 1 b-c
atom of atoms/unit cell 8 (1/8) 1 2
Cr, Mo, W, a-Fe
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1.3 Space Lattices

• Example 1.1
• Find the volume density of atoms in a crystal
  (BCC).
• Lattice constant a 5Å

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1.3 Space Lattices
The seven crystal systems
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1.3 Space Lattices

• 1.3.3 Crystal Planes and Miller Indices
• real crystals? infinitely large?? ?? ? ????
  ???? ???, ?? semi. devices? ??? surface
  properties? ? ??? ???? lattice? ???? surface?
  ???? ?? ??.
• Miller indices
• The set of integers used to describe a
  crystal plane.
• crystallographic direction and crystal
  plane? ???? ?? (h, k, l) lt????gt
• (1) ???? lattice constant(a, b, c)? ?? ???
  ?? ??.
• (2) ???? ????? ???? lattice constants? ??
  ??? ?? ??.
• (3) ???? ??? ??? ??? ??? 3??? ??
• ? Miller indices (h, k, l).

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1.3 Space Lattices
Three lattice planes
(a) (100)plane, (b) (110) plane, (c) (111)
plane

• Example 1.3
• Calculate the surface density of atoms on a
  particular plane(110) in a crystal (BCC).
  Lattice constant a 5Å

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1.3 Space Lattices
Three lattice directions and planes
(a) (100)plane and 100 directions, (b) (110)
plane and 110 directions, (c) (111) plane and
111 directions

• The hkl direction is perpendicular to the
  (hkl) plane.

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1.3 Space Lattices

• 1.3.4 The Diamond Structure
• Si, Ge diamond crystal structure, tetrahedral
  configuration
• ??? 2?? face-centered cubic sublattice? ????,
  ? lattice? ??lattice? ?? unit cell? ??????? ????
  1/4?? ????? ??? ??.
• ???? ? ??? ?? ?? 4?? valence electrons? ??
  tetrahedral bond? ??? ?? ??.

isolated atom???? ?? ??? valence electrons? 2??
s electron? 2?? p electron? ?? ???? ???, ??????
??? ?? ? ? ? ?? s electron? energy? ?? ?? p???
???? 3p3 ????(hybrid orbit)? ???? ??.
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1.3 Space Lattices

• GaAs(AIIIBV) zincblende structure
• diamond??? ????, 1?? face-centered cubic
  sublattice? Ga atom??? ???? ??, ? 1? As atom???
  ???? ??? ?? ???.

AlAs, GaP, GaSb, InAs, InP, InSb, ZnS, ZnTe
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1.4 Atomic Bonding

• ?? ??? electron configurations?
  outer(valence) shell? s p subshells? ??? ???
  ??.
• ? for example inert gases Ne(10)
  1s22s22p6
• 
  Ar(18) 1s22s22p63s23p6
• 
  Kr(36) core 4s24p6
• 
  Xe(54) core 5s25p6
• 
  Rn(86) core 6s26p6
• (1) ionic bond oppositely charged ions?
  Coulomb attraction? ?? ??.
• (2) covalent bond valence shell? s p
  subshells? ??? ??? ?? ??? atoms? their valence
  electrons? ???? bonds? ??.
• ? for example Si(14) core 3s23p2
• Ge(32) core
  4s24p2
• Ga(31, core 4s24p1)? As(33, core
  4s24p3)? ??? GaAs compound? each atom? ????? two
  s electrons two p electrons? ??.
• (3) metallic bond ????? ??? ??
• (4) Van der Waals bond the weakest of the
  chemical bonds

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1.5 Imperfection Impurities in Solids

• ?????(structure sensitive properties)
• - crystal defects? ??? ?? ??? ?? ??.
• (1) diffusion
• (2) mechanical property
• (3) thermal conduction
• (4) dielectric breakdown
• (5) electrical conduction of semiconductor
• ?????(structure non-sensitive properties)
• - crystal defects? ??? ? ??? ?? ?? ??.
• (1) ??
• (2) ????, ???
• (3) ??, ??, ??, ???
• (4) ???
• (5) ???, ??(tan d)

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1.5 Imperfection Impurities in Solids

• 1.5.1 Imperfection in Solids
• (1) point defects
• a. vacancy defect
• b. interstitial defect
• c. Frenkel defect
• d. Schottky defect

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1.5 Imperfection Impurities in Solids

• (2) line defect dislocation(??)
• ????? ??? ??? ???? ??? ?.
• a. edge dislocation
• b. screw dislocation

A screw dislocation
(3) surface defect grain boundary ????
??? ???? ??? ???? ??
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1.5 Imperfection Impurities in Solids
1.5.2 Impurities in Solids
A substitutional impurity
an interstitial impurity

• substitutional impurity impurity atoms located
  at normal lattice sites

• interstitial impurity impurity atoms located
  between normal lattice sites

• doping The technique of adding impurity atoms
  to a semiconductor material in order to change
  its conductivity.
• diffusion, ion implantation

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1.6 Growth of Semiconductor Materials

• Technology of Semiconductor Devices
• ltSemiconductor Devices? ??????gt
• Semiconductor Material??? Thin Film
  Process? ??.
• wafer? ????, ???, ??? ??.
• ??? ???? ??? ??.
• ?????? ??
• ?. ????
• 1. ?????? ????
• 2. Single Crystal ????
• Czochralski method
• 3. Wafer ????
• ?. ????
• ?. Mask ????
• ?. Wafer ????
• ?. ????
• ?. ?? ? ????

Czochralski method
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?????? ??

• I. ????
• II. Wafer ????
• A. Epitaxial growth method
• (homoepitaxy, heteroepitaxy)
• 1. Vapor Phase Epitaxy(VPE)
• 2. Liquid Phase Epitaxy(LPE)
• 3. Chemical Vapor Deposition(CVD)
• 4. Molecular Beam Epitaxy(MBE)
• 5. MOCVD (Metalorganic chemical vapor
  deposition )
• B. Thermal Oxidation of Si
• C. Diffusion and Ion Implantation
• D. Film Deposition
• 1. Vacuum Evaporation
• 2. Sputtering
• E. Lithography and Etching
• F. Metallization