An Introduction to Semiconductor Devices Donald Neamen Images and illustrations from supplements of An Introduction to Semiconductor Devices, 4 th Ed., Mc Graw Hill were used for this lecture materials. 1-1
Semiconductor Materials Elemental SC - Group 4 elements : C, Si, Ge -Sn, Pb? Compound SC - Intermetallic compound - IV-IV(Si-Ge, Si-C) - III-V(Al-P,As,Sb; Ga-N,P,As,Sb; In-N,P,As,Sb), BN - II-VI(Zn-S,Se,Te; Cd-S,Se,Te; Hg-Se,Te), MgO Alloys - Binary : Si-Ge - Ternary : (Al,Ga)As, (Al,In)As, (Cd,Mn)Te,Ga(As,P), (Ga,In)As, (Ga,In)P, (Hg,Cd)Te - Quaternary : (Al,Ga)(As,Sb), (Ga,In)(As,P) I II III IV V VI VII VIII H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca/Zn Ga Ge As Se Br Kr Cd In Sn Sb Te Hg Ti Pb Bi 1-2
Semiconductor History 1833; Fist semiconducting property of Ag 2 S by Faraday 1873; Discovery of photoconductivity of Se by Smith 1874; Observation of rectification by Braun 1879; Discovery of Hall effect (electron not yet discovered) d) 1911; The term semiconductor introduced by Konigsberg & Weiss 1927; copper oxide rectifier by Grondahl & Geiger 1931; photocell by Bergmann 1939; Development of microwave (Si) 1940s; IR detectors of sulphide, selenide, telluride 1949; Discovery of transistor action by Bardeen & Brattain 1950; Invention of transistor by Shockley, First amorphous semiconductor (α-se) ~ present; IC (electronic industry), solid state laser, organic semiconductors, artificial compound semiconductors 1-3
Physical Constants and units Avogadro's number: N A 6.02. 10 23 Boltzmann's constant k 23 1.38. 10. joule K Electronic charge (magnitude): e 1.60. 10 19.( coul ) Free electron rest mass m e 9.1094. 10 31.( kg ) Permeability of free space: μ 0 ( 4. π ). 10 7. m Permittivity of free space ε 0 14 8.854. 10. farad cm Planck's constant: h 6.625. 10 34.( joule. sec ) Proton rest mass m p 1.67. 10 27.( kg ) Speed of light in vacuum: c 2.998. 10. 10 cm sec ev 1.60. 10 19. joule (electron-volt) mev 10 3. ev μsec 10 6. sec na 10 9. amp pa 10 12. amp V volt μm. 10 6 m nm. 10 9 m Angstrom. 10 10 m Å. 10 10 m 1-4
Amorphous materials (for instance, glass and rubber) have order within a few atomic or molecular dimensions. Polycrystalline materials have a high degree of order over many atomic or molecular dimensions. These ordered regions, or single-crystal regions, vary in size and orientation with respect to one another. The single-crystal regions are called grains and are separated from one another by grain boundaries. Single-crystal materials ( for example, silicon, copper, and table salt) have a very high degree of order, or regular geometric periodicity, throughout their entire volume. The advantage of a single-crystal material is that, in general, its electrical properties are superior to those of a nonsingle-crystal material, since grain boundaries tend to degrade the electrical characteristics. Types of Solids 1-5
SiO 2 2/Si HRXTEM view of Si/SiO 2 1-6
Defects in Material Point defect (0-D) Surface defect (2-D) Vacancy Grain boundary Interstitial ex) Impurities Substitutional impurity Bulk defect (3-D) Interstitial impurity Precipitate Line defect (1-D) Edge dislocationline 1-7
Point Defects A vacancy in the crystal. A substitutional impurity in the crystal. The impurity atom is larger than the host atom. A substitutional impurity in the crystal. The impurity atom is smaller than the host atom. An interstitial impurity in the crystal. It occupies an empty space between host atoms. 1-8
Line Defects Compression Tension A Dislocation line D C Ascrew dislocation in a crystal. A edge dislocation in a crystal is a line defect which is accompanied by lattice distortion and hence a lattice strain around it. Dislocation A B line Atoms in the lower portion. Atoms in the upper portion. D C The screw dislocation in as viewed from above. 1-9
Line Defects InGaAs/AlGaAs QWs dislocations 1-10
Surface Defects Nuclei Crystallite Liquid (a) (b) Grain Grain boundary Foreign impurity Self-interstitial type atom Void, vacancy Strained bond Grain boundary Broken bond (dangling bond) (c) Solidification of a polycrystalline solid from the melt. (a) Nucleation. (b) Growth. (c) The solidified polycrystalline solid. For simplicity, cubes represent atoms. 1-11
Primitive and Unit cells Lattice Unit cell : Periodic arrangement of atoms in the crystal Dots can be used for representing the atomic arrays : Lattice Primitive unit cell 3-D unit cell Two dimensional lattice - Unit cell : A small of the crystal that can be used to reproduce the entire crystal r = p a + q b + s c (p, q, s = integers) 1-12
Basic Crystal Structures Cubic Lattices Simple Cubic (SC) Body-Centered Cubic (BCC) Face-Centered Cubic (FCC) (000) (000) 111 222 (000) 11 0 22 1 1 0 2 2 11 0 22 Q1: How many atoms are included in each unit cell? Q2: What are the packing densities? 1-13
Miller index Lattice direction c z UnitCell Geometry z Unit cell c β O α b y γ a a b x A parallelepiped is chosen to describe geometry of a unit cell. We line the x, y and z axes with the edges of the parallelepiped taking lower-left rear corner as the origin [001] x c x o z o P [121] b a y o Identification of a direction in a crystal [111] y [010] [010] -y -a a [100] [110] x [110] [111] [111] [111] [111] Directions in cubic crystal system y [111] [111] [111] [111] Family of <111> directions 1-14
Crystal plane and Miller index Index of Plane Plane 1 1 1 =,, p q s 1-15
Crystal plane and Miller index z (010) (010) z (010) (010) z intercept at x intercept at a / 2 x b c Miller Indices (hk ): 1 1 1 1 (210) 1 2 y a Unit cell y intercept at b (100) x (010) y y x (001) (110) z Identification of a plane in a crystal z (110) (111) (111) - y y x y x Various planes in cubic lattices -z 1-16
The Structure of Solids and Surfaces Bulk termination : FCC FCC (110) FCC (100) FCC (111) 1-17
The Structure of Solids and Surfaces Bulk termination : BCC BCC (110) BCC (100) BCC (111) 1-18
Crystal plane and Miller index ex) Calculate the surface density of (110) plane in fcc. a o = 4.5 Å. 2 atoms 2 atoms Surface density = = Q1: Surface density of (111) plane in fcc 8 ( a )( ) ( ) 2 0 2a0 2 4.5 10 Q2: a o = 4.75 Å. Calculate the surface densities = 6.98 10 atoms/cm 14 2 of (100) and (110) planes in bcc. 1-19
Semiconductor Structure Diamond Cubic Structure 1 [ ] fcc + 4 111 fcc Q1: How many atoms in unit cell? Q2: Coordinates of atoms in unit cell? Q3: What are the packing densities? 1-20
Semiconductor Structure Diamond cubic structure has - 8 atoms/unit cell - atomic packing factor = ~34 % - covalent bonding, tetragonal unit, 4 nearest neighbors a 0 0 1/2 0 a 0 /2 3/4 1/2 0 1/4 0 1/2 1/4 3/4 1/2 0 1 [ ] fcc + 4 111 fcc 1-21
Semiconductor Structure Zincblende structure - GaAs crystal structure Differs from the diamond structure only in that there are two types of atoms in the lattice 1 4 fcc 4 Ga atoms [ 111] ] fcc 4 4 As atoms, or vice vera. 1-22
Semiconductor Growth Purity & Doping - Purity : unintentionally doped (undesired) impurities Si : 1 per 10 9 Si atoms - Dopants : intentionally added impurities Practical functioning of devices Crystal Growth - Electronic grade poly-si Silica Impure silicon SiCl4 Ultrapure SiCl4 Poly-Si Reduction Chlorination Distilation H-Reduction - Single crystal growing Czochralski method Single crystal seed Crystal pulling and rotation 1-23
Semiconductor Growth (Mitsubishi website at http://www.egg.or.jp/msil/english/index-e.html) 1-24
Semiconductor Growth 1-25
Homework Ch.1 4 (d), 7, 10, 14, 16, 19, 25 Due date: 1-26