Terahertz Spectroscopy of CdSe Quantum DotsCdSe量子点的太赫兹光谱.ppt

Terahertz Spectroscopy of CdSe Quantum DotsCdSe量子点的太赫兹光谱
What is a quantum dot?
Nanocrystals
2-10 nm diameter
semiconductors
What is a quantum dot?
Exciton Bohr Radius
Discrete electron energy levels
Quantum confinement
Motivation
Semiconducting nanocrystals
are significant due to;
strong size dependent optical properties (quantum confinement)

applications solar cells
Terahertz gap
1 THz
= 300 µm = 33 cm-1 = 4.1 meV
Time domain terahertz Spectrometer
The pulse width = ΔtFWHM/√2 = 17.6±0.5 fs
(A Gaussian pulse is assumed)
Terahertz Signal
Fourier Transform
To obtain the response of the sample to the THz radiation 2 measurements are made
THz electric field transmitted through the empty cell
THz electric field transmitted through the sample cell
Terahertz signal
Doping
Intentionally adding impurities to change electrical and optical properties
Add free electrons to conduction band or free holes in valence band
Tin and Indium dopants
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