The Ancient “Periodic Table”

1. The Ancient “Periodic Table”

2. Survey of the Periodic TableSemiconductor MaterialsFormed from Atoms in Various Columns

3. Group IVCrystalline MaterialsElemental Semiconductors formed from atoms in Column IV • C (carbon):Different Crystal Phases Diamond Structure: Diamond!Insulator or semiconductor Graphite: A metal.The most common carbon solid. Fullerenes:Based on Buckminsterfullerene.“Bucky Balls”, Nanotubes, Insulator, Semiconductor or Metal depending on preparation. Clathrates: Possible new forms of C solids? Semiconductor or semimetal, compounds,… Recent Research!! • Si (silicon):Different Crystal Phases Diamond Structure: A Semiconductor.The most common Si solid.Clathrates: “New” forms of Si solids.Semiconductor, Semimetal, Compounds,…. Recent Research

4. Group IVCrystalline Materials • Ge (germanium):Different Crystal Phases Diamond Structure: A Semiconductor.The most common Ge solid. Clathrates: “New” forms of Ge solids. Semiconductor, Semimetal, Compounds,….Recent Research • Sn (tin):Different Crystal Phases Diamond Structure:Gray tin or α-Sn.A Semimetal Body Centered Tetragonal Structure: White tin or β-Sn. A Metal, The most common Sn solid. Clathrates: “New” forms of Sn solids. Semiconductor, Semimetal, Compounds,….Recent Research • Pb (lead):Face Centered Cubic Structure:A Metal.

5. Group IVMaterialsBandgaps & Near-Neighbor Distances for Solids in Lattices with the Diamond Structure Decreasing BandgapEgcorrelates with Increasing Nearest Neighbor Bond Lengthd Atom Eg (eV) d (Å) C 6.0 2.07 Si 1.1 2.35 Ge 0.7 2.44 Sn(a semimetal) 0.0 2.80 Pb(a metal) 0.0 1.63 Not diamond structure!

6. Elemental Semiconductors • Mainly, these are from Column IV elements • C (diamond), Si, Ge, Sn (gray tin or α-Sn) Tetrahedrally bonded in the diamond crystal structure. Each atom has 4 nearest-neighbors. Bonding:sp3covalent bonds. • Also! Some Column V & Column VI elements are semiconductors! P, A 3-fold coordinated lattice. S, Se, Te 5-fold coordinated lattices.

7. III-V CompoundsPeriodic Table Columns III & V Column III Column V B N Al P Ga As In Sb Tl  not used Bi  BN, BP, BAs; AlN, AlP, AlAs, AlSb GaN, GaP, GaAs, GaSb; InP, InAs, InSb,….

8. III-V Compounds • Applications:IR detectors, LED’s, switches • BN, BP, BAs; AlN, AlP, AlAs, AlSb GaN, GaP, GaAs, GaSb; InP, InAs, InSb,…. The bandgap decreases & the interatomic distance increases as you go down the periodic table Tetrahedral coordination!Mosthave the zincblende crystal structure. Some (B compounds & N compounds): have the wurtzite crystal structure. Bonding:Is not purely covalent! The charge separation due to the valence differences leads to Partially ionic bonds.

9. II-VI CompoundsPeriodic Table Columns II & VI Column II Column VI Zn O Cd S Hg Se Mn  sometimes Te not used  Po  ZnO, ZnS, ZnSe, ZnTe; CdS, CdSe, CdTe HgS, HgSe, HgTe,some compounds withMn….

10. II-VI Compounds • Applications:IR detectors, LED’s, switches ZnO, ZnS, ZnSe, ZnTe; CdS, CdSe, CdTe HgS, HgSe, HgTe(semimetals); compounds withMn The bandgap decreases & the interatomic distance increases as you go down the periodic table Large bandgaps!Except for Hg compounds, which are semimetals with zero gaps. Tetrahedral coordination!Some zincblende & some wurtzite crystal structures. Bonding:Charge separation due to valence difference is large.  More ionic than covalent!

11. IV- IV CompoundsPeriodic Table Column IV Column IV C Si Ge Sn  SiC Other compounds:GeC, SnC, SiGe, SiSn, GeSncannot be made or cannot be made without species segregation or are not semiconductors. SiC:zincblende (semiconductor), & hexagonal close packed (large gap insulator). AlsoMANY other crystal structures!

12. IV- VI CompoundsPeriodic Table Columns IV & VI Column IV Column VI C O Si S Ge Se Sn Te Pb PbS, PbTe, PbSe, SnS Others: SnTe, GeSe, … can’t be made, can’t be made without segregation, aren’t binary compounds, or aren’t semiconductors.

13. IV-VI Compounds • Applications: IR detectors, switches • PbS, PbTehave the zincblende crystal structure • Others: 6-fold coordination ~ 100% ionic bonding Small bandgaps (IR detectors)

14. I-VII CompoundsPeriodic Table Columns I & VII • Mostly insulators:NaCl, CsCl, … • Notetrahedral coordination! 6 or 8 fold coordination. ~ 100% ionic bonding • Have the NaCl or CsCl crystal structures Large bandgaps

15. Oxide CompoundsA category all their own • Most are good insulators(large bandgaps) • A few are semiconductors: CuO, Cu2O, ZnO Not well understood Very few applications • Except for ZnO (ultrasonic transducer) • At low T, some oxides are superconductors Many “high” Tcsuperconductors are based onLa2CuO4 (Tc~ 135K)

16. Some OtherSemiconductor Materials • “Alloy” mixturesof elemental materials (binary alloys): SixGe1-x ,... (0 ≤ x ≤ 1) • “Alloy” mixturesof binary compounds (ternary alloys): Ga1-xAlxAs, GaAs1-xPx,… (0 ≤ x ≤ 1) • “Alloy” mixturesof binary compounds with mixtures on both sublattices (quaternary alloys): Ga1-xAlxAs1-yPy, .., (0 ≤ x ≤ 1, 0 ≤ y ≤ 1) • Vary x & y  varies the bandgap & other properties. “BANDGAP ENGINEERING!”

17. “Exotic” Semiconductors • Layered compounds:PbI2, MoS2, PbCl2, … • Strong Covalent bonding within layers weak Van Der Waals bonding between layers • Effectively “2 dimensional solids” Electronic & vibrational properties have ~ 2 dimensional character. • Organic semiconductors • Polyacetyline:(CH2)n: “Great promise for future applications” (I’ve heard this for  30 years!) • Not well understood

18. Other Semiconductors • Magnetic semiconductors • Compounds withMn & / or Eu(& other magnetic ions) • Simultaneously semiconducting & magnetic EuS, CdxMn1-xTe, Optical modulators,… • Others(see YC, p 4) I-II-(VI)2 & II-IV-(V)2 compounds • AgGaS2, ZnSiP2, …., Tetrahedral bonding V2-(VI)3 compounds • As2Se3….