QUANTUM TRANSPORT IN SEMICONDUCTOR NANOSTRUCTURES

Conductor(Cu, Ag..)

Semiconductor(Si, GaAs..)

Insulator(SiO2,..)

Resistivity(Ohm.cm) 26 10~10 92 10~10 2214 10~10

insSCmetal

SEMICONDUCTORA SEMICONDUCTOR IS A MATERIAL WHICH HAS ELECTRICAL CONDUCTIVITY

BETWEEN THAT OF CONDUCTOR AND THAT OF AN INSULATOR.

TABLE NO.1

insSCmetal RRR

Conduction Band (CB)

Valence Band (VB)

METAL INSULATOR SEMICONDUCTOR

Energy gap (Eg)Energy gap (Eg)

FIG NO.1---ENERGY BANDS FOR METALS, INSULATORS AND SEMICONDUCTORS

TYPES OF SEMICONDUCTORS

Intrinsic SC----purest form, no doping.

Extrinsic SC----mixture of 2 or more elements, has been doped.

Extrinsic are further divided into:P type----majority charge carriers are holes.N type----majority charge carriers are electrons.

A10101 9 mnm

Is Nanometer small or large?

Lattice constant: nm01 10~10

lF of bulk: nm21 10~10

Effective Bohr Radius: nm110~

Length scales in semiconductors (SC’s)

Coherent length:

Mean free path:

0.1nm

1m

100nm

10nm

1nm

100m

10m

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Nanostructures constructed from inorganic solids like semiconductors have new electronic and optical properties due to their size and quantization effects . The quantization effects reflect the fundamental characteristics of structures as soon as their size falls below a certain limit. An example of the simplest nanostructure is the quantum dot formed from the energy well of certain semiconductor materials with 5-10nm thickness sandwiched between other semiconductors with normal properties.

SC NANOSTRUCTURES

Scanning Electron Microscope (SEM)

FIG NO.2—SELF ASSEMBLED QUANTUM DOTS AND SPACING BETWEEN THEM.

NANO TECHNOLOGY

Semiconductor nano-technology,Material engineering.etc…

Quantum-dot lasersPhoto-detectorsSingle electron devicesSingle photon devicesQuantum computingetc….

Advanced Applications

QUANTUM TRANSPORT

Diffusive Transport-----The process by which particles of liquids or gases move from an area of higher concentration to an area of lower concentration.

Ballistic Transport----- Motion of electrons in ultra-small regions in semiconductor structures at very high electric field with velocities much higher than their equilibrium thermal velocity. Ballistic electrons are not subjected to scattering

BALLISTIC TRANSPORTATION

• Ballistic Transportation is observed when the mean free path of the electron is (much) longer than the dimension of the medium through which the electron travels.

• The electron alters its motion only upon collision with the walls

• The mean free path can be increased by reducing the number of impurities in a crystal or by lowering its temperature.

DIFFUSIVE TRANSPORTATION

• Transport of electric charge is a time-dependent process.

• In semiconductor nanostructures both classical and quantum size effects appear.

FIG NO.3

DRUDE MODEL

• The is an application of kinetic theory.• Assumes that the microscopic behavior of

electrons in a solid may be treated classically and looks much like a pinball machine, with a sea of constantly jittering electrons bouncing and re-bouncing off heavier, relatively immobile positive ions.

Two most significant results of the Drude model are an electronic equation of motion

And a linear relationship between current density and electric field

 

 

 

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