Semiconductor Physics. Introduction to Semiconductors Information from Kittel’s book (Ch. 8) + many outside sources!! Most lectures on semiconductors will be based on those prepared for Physics 5335 Semiconductor Physics. That course was taught last in Fall, 2016. It is scheduled to be taught next in the Fall of 2018!!

As discussed at the start of the semester, Phys. 5335, Semiconductor Physics, has overlap with this Solid State course. But they are complementary & are NOT the same. I encourage you grad students to take Phys. 5335! More information (last update, Dec., 2014!!) about Phys. 5335 is on the course webpages: 5335 Homepage: http://www.phys.ttu.edu/~cmyles/Phys5335/5335.html 5335 Lecture Page: http://www.phys.ttu.edu/~cmyles/Phys5335/lectures.html!

An Alternate Semiconductor Definition!

What is a Semiconductor? Kittel Ch. 8 & many other sources Classification of Solids by their Conductivity/Resistivity: (σ = conductivity, ρ = resistivity)

What is a Semiconductor? Kittel Ch. 8 & many other sources Classification of Solids by their Conductivity/Resistivity: (σ = conductivity, ρ = resistivity) Metals: Good Conductors! : 103 ≤ σ ≤ 108 (Ω-cm)-1 ; 10-8 ≤ ρ ≤ 10-3 Ω-cm

What is a Semiconductor? Kittel Ch. 8 & many other sources Classification of Solids by their Conductivity/Resistivity: (σ = conductivity, ρ = resistivity) Metals: Good Conductors! : 103 ≤ σ ≤ 108 (Ω-cm)-1 ; 10-8 ≤ ρ ≤ 10-3 Ω-cm Insulators: Poor Conductors! σ ≤ 10-8 (Ω-cm)-1 ; ρ ≥ 108 Ω-cm

What is a Semiconductor? Kittel Ch. 8 & many other sources Classification of Solids by their Conductivity/Resistivity: (σ = conductivity, ρ = resistivity) Metals: Good Conductors! : 103 ≤ σ ≤ 108 (Ω-cm)-1 ; 10-8 ≤ ρ ≤ 10-3 Ω-cm Insulators: Poor Conductors! σ ≤ 10-8 (Ω-cm)-1 ; ρ ≥ 108 Ω-cm Semiconductors/Semimetals: 10-8 ≤ σ ≤ 103 (Ω-cm)-1; 10-3 ≤ ρ ≤ 108 Ω-cm

What is a Semiconductor? Kittel Ch. 8 & many other sources Classification of Solids by their Conductivity/Resistivity: (σ = conductivity, ρ = resistivity) Metals: Good Conductors! : 103 ≤ σ ≤ 108 (Ω-cm)-1 ; 10-8 ≤ ρ ≤ 10-3 Ω-cm Insulators: Poor Conductors! σ ≤ 10-8 (Ω-cm)-1 ; ρ ≥ 108 Ω-cm Semiconductors/Semimetals: 10-8 ≤ σ ≤ 103 (Ω-cm)-1; 10-3 ≤ ρ ≤ 108 Ω-cm Note the HUGE range! Note also that there are no rigid boundaries!

Metals & Insulators: Measured resistivities range over more than 30 orders of magnitude! Material Resistivity (Ωm) (295K) Resistivity (Ωm) (4K) “Pure” Metals   Semi- conductors Ge (pure) 5  102 1012 Insulators Potassium 10-5 10-12 Copper 2  10-6 10-10 Diamond 1014 1014 P.T.F.E 1020 1020 (Polytetrafluoroethylene)

Metals, Insulators & Semiconductors At low temperatures, all materials are insulators or metals. 1020- Diamond 1010- Resistivity (Ωm) Germanium Pure Metals: Resistivity increases rapidly with increasing temperature. 100 - Copper 10-10- 100 200 300 Temperature (K) Semiconductors: Resistivity decreases rapidly with increasing temperature. Semiconductors have resistivities intermediate between metals and insulators at room temperature.

Semiconductors Conductivity/Resistivity Definition  Metals   Semimetals 

Semiconductors Conductivity/Resistivity Definition Note the wide range of conductivity!  Metals   Semimetals 

Conductivity/Resistivity of Some Materials Semiconductors!

Conductivity of Some Materials

One Way to Classify “Electronic Materials”

Semiconductors: Bandgap Definition a semiconductor must also be Semiconductors are ~ Small Bandgap Insulators (we defined bandgap Eg earlier). Strictly speaking, a semiconductor must also be capable of being doped (we’ll define doping later).

Semiconductors: Bandgap Definition a semiconductor must also be Semiconductors are ~ Small Bandgap Insulators (we defined bandgap Eg earlier). Strictly speaking, a semiconductor must also be capable of being doped (we’ll define doping later). Typical Bandgaps Semiconductors: 0 ~ ≤ Eg ≤ ~ 3 eV

Semiconductors: Bandgap Definition a semiconductor must also be Semiconductors are ~ Small Bandgap Insulators (we defined bandgap Eg earlier). Strictly speaking, a semiconductor must also be capable of being doped (we’ll define doping later). Typical Bandgaps Semiconductors: 0 ~ ≤ Eg ≤ ~ 3 eV Metals & Semimetals: Eg = 0 eV

Semiconductors: Bandgap Definition a semiconductor must also be Semiconductors are ~ Small Bandgap Insulators (we defined bandgap Eg earlier). Strictly speaking, a semiconductor must also be capable of being doped (we’ll define doping later). Typical Bandgaps Semiconductors: 0 ~ ≤ Eg ≤ ~ 3 eV Metals & Semimetals: Eg = 0 eV Insulators: Eg ≥ 3 eV

An Exception is Diamond Eg = ~ 6 eV. Diamond is usually considered an insulator, but it can be doped & used as a semiconductor! Also, sometimes there is confusing terminology like: GaAs: Eg = 1.5 eV is sometimes called semi-insulating!

More Semiconductor Characteristics In pure materials (very rare): The electrical conductivity σ  exp(cT) T = Kelvin Temperature, c = constant

More Semiconductor Characteristics In pure materials (very rare): The electrical conductivity σ  exp(cT) T = Kelvin Temperature, c = constant In Impure materials (most of them!): The electrical conductivity σ depends strongly on impurity concentrations. “Doping” means to add impurities to change σ

More Semiconductor Characteristics In pure materials (very rare): The electrical conductivity σ  exp(cT) T = Kelvin Temperature, c = constant In Impure materials (most): The electrical conductivity σ depends strongly on impurity concentrations. “Doping” means to add impurities to change σ The electrical conductivity σ can be changed by light or electron radiation & by injection of electrons at contacts.

More Semiconductor Characteristics In pure materials (very rare): The electrical conductivity σ  exp(cT) T = Kelvin Temperature, c = constant In Impure materials (most): The electrical conductivity σ depends strongly on impurity concentrations. “Doping” means to add impurities to change σ The electrical conductivity σ can be changed by light or electron radiation & by injection of electrons at contacts Transport of charge can occur by the motion of electrons or holes (defined later).

The Best Known Semiconductor is, of course, Silicon (Si)

The Best Known Semiconductor is, of course, Silicon (Si) However, there are HUNDREDS (THOUSANDS?) of others!

The Best Known Semiconductor is, of course, Silicon (Si) However, there are HUNDREDS (THOUSANDS?) of others! Elemental: Si, Ge, C (diamond)

The Best Known Semiconductor is, of course, Silicon (Si) However, there are HUNDREDS (THOUSANDS?) of others! Elemental: Si, Ge, C (diamond) Binary Compounds: GaAs, InP, .

The Best Known Semiconductor is, of course, Silicon (Si) However, there are HUNDREDS (THOUSANDS?) of others! Elemental: Si, Ge, C (diamond) Binary Compounds: GaAs, InP, . Organic Compounds: (CH)n (polyacetyline)

The Best Known Semiconductor is, of course, Silicon (Si) However, there are HUNDREDS (THOUSANDS?) of others! Elemental: Si, Ge, C (diamond) Binary Compounds: GaAs, InP, . Organic Compounds: (CH)n (polyacetyline) Magnetic Semiconductors: CdxMn1-xTe,…

The Best Known Semiconductor is, of course, Silicon (Si) However, there are HUNDREDS (THOUSANDS?) of others! Elemental: Si, Ge, C (diamond) Binary Compounds: GaAs, InP, . Organic Compounds: (CH)n (polyacetyline) Magnetic Semiconductors: CdxMn1-xTe,… Ferroelectric Semiconductors: SbI, …

The Best Known Semiconductor is, of course, Silicon (Si) However, there are HUNDREDS (THOUSANDS?) of others! Elemental: Si, Ge, C (diamond) Binary Compounds: GaAs, InP, . Organic Compounds: (CH)n (polyacetyline) Magnetic Semiconductors: CdxMn1-xTe,… Ferroelectric Semiconductors: SbI, … Superconducting Compounds: GeTe, SrTiO3, ..(“High Tc materials”)

Group IV Materials & III-V & II-VI Compounds The Periodic Table: The Relevant Parts for Elemental & Binary Semiconductors III IV V VI II II Group IV Materials & III-V & II-VI Compounds

Some Elements & Compounds which can be Semiconductors (Purple!)

Semiconductors (Main Constituents)

The Periodic Table Cloth!

Group IV Elements & III-V & II-VI Compounds

Group IV Elements & Compounds: Trends Diamond Diamond Lattices (α-Sn or gray tin) The band gap (mostly) decreases & n-n distance (mostly) increases going down a column or going within a row from IV elements to III-V compounds to II-VI compounds.

III-V & II-VI Compounds Trends Zincblende or Wurtzite Lattices The band gap (mostly) decreases & n-n distance (mostly) increases going down a column or going within a row from IV elements to III-V compounds to II-VI compounds.

Many Materials of Interest: Have crystal lattice structures = Diamond or Zincblende (discussed in detail earlier!): Each atom is tetrahedrally coordinated with four (4) nearest-neighbors. The bonding is (mostly) sp3 hybrid bonding (strongly covalent). Two atoms/unit cell (repeated to form an infinite solid).

Zincblende (ZnS) Lattice Zincblende Lattice The Cubic Unit Cell. If all atoms are the same, it becomes the Diamond Lattice! Zincblende Lattice A Tetrahedral Bonding Configuration

Zincblende/Diamond Lattices Cubic Unit Cell Zincblende Lattice Cubic Unit Cell Semiconductor Physicists & Engineers need to know these structures!

Semiconductor Physicists & Engineers need to know these structures! Diamond Lattice Diamond Lattice The Cubic Unit C`ell. Semiconductor Physicists & Engineers need to know these structures!

Zincblende (ZnS) Lattice Zincblende Lattice The Cubic Unit Cell.

Some Materials of Interest: Have crystal lattice structures = Wurtzite Structure (discussed earlier!): Similar to Zincblende, but has hexagonal symmetry instead of a cubic. Each atom is tetrahedrally coordinated with four (4) nearest-neighbors. The bonding is (mostly) sp3 hybrid bonding (strongly covalent). Two atoms/unit cell (repeated to form an infinite solid).

Semiconductor Physicists & Engineers need to know these structures! Wurtzite Lattice Semiconductor Physicists & Engineers need to know these structures!

Room Temperature Properties of Some Semiconductor Materials

Room Temperature Properties of Some Semiconductors

Lattice Constants of Some Semiconductors

Room Temperature Properties of Si, Ge, & GaAs