Lesson 4:
The physics of low-dimensional
semiconductors
A) Basic properties of 2D semiconductor nanostructures
Quantum well for electrons
Thin film of a pure or composed material
Heterostructure
Common physics
a) Band Engineering
b) Thickness Engineering
Heterostructure (MBE) AlGaAs GaAs AlGaAs
- Interband processes - Intraband processes
E(z) engineering (modulation)
Superlattice
Electronic transport???
V
Electric Field Applied Or
Magnetic Field Applied
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<<l
ekT<<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
V0
A.2) Superlattices
- Kronig-Penney model of a superlattices
Minibands Minigaps
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)
E C (e 2 /C) and single electron effects
ΔE E C kT
3D: ΔE>>E C 2D: ΔE>>E C 1D: ΔE>>E C 0D: ΔE~E C
3D, 2D, 1D 0D
ΔE EC kT
ΔE kT
EC
Density of electronic states in a quantum dots
