The Ancient “Periodic Table”

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

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

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

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 Si Ge Sn (a semimetal) Pb (a metal) Not diamond structure!

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.

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,….

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.

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….

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

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!

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

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)

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

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)

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!”

“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

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