1. The Ancient “Periodic Table”

2. Survey of the Periodic Table Semiconductor Materials Formed from Atoms in Various Columns

3. Group IV Crystalline Materials Elemental 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. 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. Group IV Crystalline Materials

5. Group IV Materials Bandgaps & Near-Neighbor Distances for Solids in Lattices with the Diamond Structure Decreasing Bandgap E g correlates with Increasing Nearest Neighbor Bond Length d Atom E g (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: sp 3 covalent 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 Compounds Periodic 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! Most have 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 Compounds Periodic 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 with Mn….

10. Applications: IR detectors, LED’s, switches ZnO, ZnS, ZnSe, ZnTe; CdS, CdSe, CdTe HgS, HgSe, HgTe (semimetals) ; compounds with Mn 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! II-VI Compounds

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

12. 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. IV- VI Compounds Periodic Table Columns IV & VI

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

14. Mostly insulators: NaCl, CsCl, … No tetrahedral coordination! 6 or 8 fold coordination. ~ 100% ionic bonding Have the NaCl or CsCl crystal structures Large bandgaps I-VII Compounds Periodic Table Columns I & VII

15. Oxide Compounds A category all their own Most are good insulators (large bandgaps) A few are semiconductors: CuO, Cu 2 O, ZnO Not well understood Very few applications –Except for ZnO (ultrasonic transducer) At low T, some oxides are superconductors Many “high” T c superconductors are based on La 2 CuO 4 (T c ~ 135K)

16. Some Other Semiconductor Materials “Alloy” mixtures of elemental materials (binary alloys): Si x Ge 1-x,... (0 ≤ x ≤ 1) “Alloy” mixtures of binary compounds (ternary alloys): Ga 1-x Al x As, GaAs 1-x P x,… (0 ≤ x ≤ 1 ) “Alloy” mixtures of binary compounds with mixtures on both sublattices (quaternary alloys): Ga 1-x Al x As 1-y P y,.., (0 ≤ x ≤ 1, 0 ≤ y ≤ 1) Vary x & y  varies the bandgap & other properties. “BANDGAP ENGINEERING!”

17. “Exotic” Semiconductors Layered compounds: PbI 2, MoS 2, PbCl 2, … –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: (CH 2 ) n : “Great promise for future applications” (I’ve heard this for  30 years!) –Not well understood

18. Magnetic semiconductors –Compounds with Mn & / or Eu (& other magnetic ions) –Simultaneously semiconducting & magnetic EuS, Cd x Mn 1-x Te, Optical modulators,… Others (see YC, p 4) I-II-(VI) 2 & II-IV-(V) 2 compounds AgGaS 2, ZnSiP 2, …., Tetrahedral bonding V 2 -(VI) 3 compounds As 2 Se 3 …. Other Semiconductors