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Lesson 4:
The physics of low-dimensional
semiconductors
A) Basic properties of 2D semiconductor nanostructures
Quantum well for electrons
Heterostructure
Thin film of a pure or
composed material
Common physics
Heterostructure (MBE)
AlGaAs GaAs AlGaAs
- Interband processes
- Intraband processes
E(z) engineering
(modulation)
a) Band Engineering
b) Thickness Engineering
Superlattice
Electronic transport???
Electric Field Applied
Or
Magnetic Field Applied
V
Electronic transport occurs determined by:
A) A new band diagram (modified by the electric or magnetic field)
B) Electronic density of states
C) Tunnelling phenomena
D) Temperature
E) Electroniuc coupling
F) Scattering phenomena
kT
a<<le
kT<<ΔE
Interband Transitions
Density of electronic states in a quantum well
3D
2D
A1) Parabolic and triangular quantum wells
- Parabolic well
- Triangular well
V
V=0
V0
A.2) Superlattices
- Kronig-Penney model of a superlattices
Minigaps
Minibands
A3) Modulation-doped heterojunctions
A4) MOSFET structures
2D Electron Gas
B) Quantum wires (1D semiconductor nanostructures)
C Nanotubes
Si, Ge nanowires
V
Electronic transport occurs determined by:
A) A new band diagram (modified by the electric or magnetic field)
B) Electronic density of states
C) Tunnelling phenomena
D) Temperature
E) Electroniuc coupling
F) Scattering phenomena
Density of electronic states in a quantum wire
C) Quantum dots (0D semiconductor nanostructures)
Current???
Charging energy (ionization energy)
EC (e2/C) and single electron effects
ΔE
EC
kT
3D: ΔE>>EC
2D: ΔE>>EC
1D: ΔE>>EC
0D: ΔE~EC
3D, 2D, 1D
ΔE
EC kT
0D
EC
ΔE
kT
Density of electronic states in a quantum dots