CHEM01200604009 Sreejith Kaniyankandy - Homi Bhabha ...

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gE ( )
2Em
2 3
3
(1.25)
For a Quantum Well where in two dimensions particles are free, we can write DOS as
m
g2D( E)
(1.26)
2
For Quantum Wire DOS is,
( ) 1 2m
g1D E (1.27)
E
For Quantum Dots levels are fully discrete.
Below schematic in fig 1.4 gives DOS versus E for different dimensionality.
1.3. Carrier Relaxation in Quantum Dots
In the previous section, discussion was mainly concentrated on the effects of
quantization on electronic properties. These changes in electronic properties not only affect
steady state properties but also affect dynamics properties. Several studies have shown how
relaxation dynamics in quantum dots are unique. Understanding the relaxation mechanisms
helps in achieving a degree of control over properties which in turn helps in optimizing
performance of devices constructed from quantum dots.
On photoexcitation with
h E (Band Gap) of the semiconductor, electrons and
g
holes are produced in Conduction and Valence Band respectively. In bulk semiconductors
energy spacing within individual bands are smaller than thermal energy therefore cooling
(relaxation in individual bands or intraband transitions) can happen via a phonon emission
processes. In a quantum confined system the spacing in the individual bands are very often