Physics for Electrical Engineering: Unit V: Nano Devices
Density of states in quantum well, quantum wire and quantum dot structure
Nano Devices
In quantum well structure, the electrons can move freely in two directions (2D) and confined in only one direction. The density of state of the quantum well structure
DENSITY OF STATES IN QUANTUM WELL, QUANTUM WIRE AND QUANTUM DOT
STRUCTURE
Bulk
Structure
The
density of state of a bulk material is given by
where,
Ec - 'bottom of conduction band energy
m*
- effective mass of electron
The
density of state curve is parabolic as shown in fig. 5.7(a).
Quantum
Well Structure
In
quantum well structure, the electrons can move freely in two directions (2D)
and confined in only one direction. The density of state of the quantum well
structure
The
density of state function is constant and it gives step like function with
energy as shown in fig. 5.7 (b).
Quantum
Wire Structure
The
quantum wire structure provides only one non confinement direction, ie., the
carrier can move freely along one direction (1D). The remaining two directions
are confined for charge carrier.
The
density of states of quantum wire is proportional to 1/√E. The density of state
for this structure is given as
The
density of states function with energy is as shown in fig. 5.7(c).
Quantum
dot
In
quantum dot all the directions are confined and no direction (OD) in which
electron movement is free. The density of state for this structure is given by
Z
(E) = δ (E - Ei), i = 1, 2, 3
For
quantum dot (OD) or nano particle, the permitted energy values are not
continuous but form discrete bunches of varying densities. Thus, density of
energy levels appear as discrete line as in fig. 5.7(d).
Table
5.2 gives different quantum structures and their corresponding density of state
functions.
Table
5.2
Density
of states as a function of dimensionality of the structure
Physics for Electrical Engineering: Unit V: Nano Devices : Tag: : Nano Devices - Density of states in quantum well, quantum wire and quantum dot structure
Physics for Electrical Engineering: Unit V: Nano Devices
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Physics for Electrical Engineering
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