Physics for Information Science: Unit V: Nanodevices and Quantum Computing
Band Gap on Nano Materials
Very few atoms in a material not only causes the energy states to spread out but also widens the band gap for semiconductors and insulators.
BAND
GAP ON NANO MATERIALS
Very
few atoms in a material not only causes the energy states to spread out but
also widens the band gap for semiconductors and insulators as shown in Fig.
5.17.
Fig.
5.17 The band gap gets bigger as the material gets smaller. Once the volume is
reduced from that of a solid, which has bands for sublevels, to that of a
nanomaterial, which has distinct splits in each sub level, the band gap will
widen even if only a few atoms are removed. This allows us to tune the
electronic and optical characteristics of a nanomaterial.
When
the energy states are discrete, the addition or removal of just a few atoms
adjusts the boundaries of the band gap. This is because once two atoms are next
to each other, the sublevels split and then begin to broaden into bands.
The
broader the bands get, the smaller the band gaps between them get. Finally, the
bands reach a point where they will not get any wider no matter how many atoms
are in the solid.
In
the case of quantum dots, the smaller the particle, the bigger the band gap.
The
band gap gets bigger as the material gets smaller.
Once
volume is reduced from that of a solid, which has bands for sublevels, to that
of a nanomaterial, which has distinct splits in each sublevel, the band gap
will widen if only a few atoms are removed.
This
allows us to 'tune' the electronic and optical characteristics of the
nanomaterial.
When
an electron is excited across the band gap into the conduction band, it rarely
stays there very long. It releases its energy in the form of a photon as it
falls back to the valence band.
The
energy of this photon is equal to the energy the electron loses in its
transition: it is same as the band gap energy.
Thus,
if we change a material's band gap energy, we change the electromagnetic
radiation it emits. This phenomena is especially used in optical applications.
Physics for Information Science: Unit V: Nanodevices and Quantum Computing : Tag: : - Band Gap on Nano Materials
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