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Berkeley ELENG 130 - Semiconductor Fundamentals

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Semiconductor FundamentalsWhat is a Semiconductor?Semiconductor MaterialsFrom Hydrogen to SiliconThe Silicon AtomThe Si CrystalHow Many Silicon Atoms per cm-3?Compound SemiconductorsCrystallographic NotationCrystallographic Planes and Si WafersCrystallographic Planes in SiSummarySemiconductor FundamentalsOUTLINE• General material properties• Crystal structure• Crystallographic notationRead: Chapter 1EE130 Lecture 1, Slide 2Spring 2007What is a Semiconductor?•Low resistivity => “conductor”•High resistivity => “insulator”•Intermediate resistivity => “semiconductor”–conductivity lies between that of conductors and insulators–generally crystalline in structure for IC devices•In recent years, however, non-crystalline semiconductors have become commercially very importantpolycrystalline amorphous crystallineEE130 Lecture 1, Slide 3Spring 2007Semiconductor MaterialsElemental: Compound:Alloy:EE130 Lecture 1, Slide 4Spring 2007From Hydrogen to Silicon11s 2s 2p 3s 3p 3d1 H 11s12 He 21s23 Li 2 11s2 2s14 Be 2 21s2 2s25 B 2 2 11s2 2s2 2p16 C 2 2 21s2 2s2 2p27 N 2 2 31s2 2s2 2p38 O 2 2 41s2 2s2 2p49 F 2 2 51s2 2s2 2p510 Ne 2 2 61s2 2s2 2p611 Na 2 2 6 11s2 2s2 2p6 3s112 Mg 2 2 6 21s2 2s2 2p6 3s213 Al 2 2 6 2 11s2 2s2 2p6 3s2 3p114 Si 2 2 6 2 21s2 2s2 2p6 3s2 3p215 P 2 2 6 2 31s2 2s2 2p6 3s2 3p316 S 2 2 6 2 41s2 2s2 2p6 3s2 3p417 Cl 2 2 6 2 51s2 2s2 2p6 3s2 3p518 Ar 2 2 6 2 61s2 2s2 2p6 3s2 3p6ZNameNotation23# of ElectronsEE130 Lecture 1, Slide 5Spring 2007The Silicon Atom•14 electrons occupying the 1st 3 energy levels:–1s, 2s, 2p orbitals filled by 10 electrons–3s, 3p orbitals filled by 4 electrons To minimize the overall energy, the 3s and 3p orbitals hybridize to form 4 tetrahedral 3sp orbitalsEach has one electron and is capable of forming a bond with a neighboring atomEE130 Lecture 1, Slide 6Spring 2007“diamond cubic” latticeThe Si Crystal•Each Si atom has 4 nearest neighbors•lattice constant = 5.431ÅEE130 Lecture 1, Slide 7Spring 2007How Many Silicon Atoms per cm-3?• Number of atoms in a unit cell:• 4 atoms completely inside cell• Each of the 8 atoms on corners are shared among cells  count as 1 atom inside cell• Each of the 6 atoms on the faces are shared among 2 cells  count as 3 atoms inside cell Total number inside the cell = 4 + 1 + 3 = 8• Cell volume:(.543 nm)3 = 1.6 x 10-22 cm3• Density of silicon atoms = (8 atoms) / (cell volume) = 5 x 1022 atoms/cm3EE130 Lecture 1, Slide 8Spring 2007Compound SemiconductorsG aA s• “zincblende” structure• III-V compound semiconductors: GaAs, GaP, GaN, etc. important for optoelectronics and high-speed ICsEE130 Lecture 1, Slide 9Spring 2007Crystallographic NotationNotation Interpretation( h k l )crystal plane{ h k l }equivalent planes[ h k l ]crystal direction< h k l >equivalent directionsh: inverse x-intercept of planek: inverse y-intercept of planel: inverse z-intercept of plane(Intercept values are in multiples of the lattice constant;h, k and l are reduced to 3 integers having the same ratio.)Miller Indices:EE130 Lecture 1, Slide 10Spring 2007Crystallographic Planes and Si WafersSilicon wafers are usually cut along a {100} plane with a flat or notch to orient the wafer during IC fabrication:EE130 Lecture 1, Slide 11Spring 2007Unit cell:View in <100> directionCrystallographic Planes in SiView in <110> directionView in <111> directionEE130 Lecture 1, Slide 12Spring 2007Summary•Crystalline Si:–4 valence electrons per atom–diamond lattice•each atom has 4 nearest neighbors–5 x 1022 atoms/cm3•Crystallographic notation–Miller indices are used to designate planes and directions within a crystalline


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Berkeley ELENG 130 - Semiconductor Fundamentals

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