Transcript Colloidal Core/Shell quantum dots in our lab

胶体半导体量子点的光电性质研究
张家雨，崔一平
东南大学电子工程系
北京，2009年5月
半导体纳米材料由于量子局域效应呈现许多迥异
于体材料的性质，例如其尺寸能大幅度地调节其
能带结构，这在荧光、激光发射、太阳能电池和
光电调制等方面有广泛的应用前景。
国内外已对半导体量子结构进行了几十年的深入
研究，目前半导体一维量子结构－－量子阱和超
晶格已得到广泛应用，其二/三维量子结构－－
量子线/点已有三十年的广泛研究，提出了各种
制备方法。
目前研究较多的量子点制备方法有半导体外延生长
（以MBE 为代表）和化学胶体方法等
Fabrication of Quantum Dots (QDs)
MBE deposition
group III-V, IV semiconductor
Good stability;
Compatible with the semiconductor technology;
Easy to fabricate electrically-driven device
Electrically-pumped MBE QDs’ Lasing has been realized, but
films with high QDs’density and homogeneous QDs’ size are
necessary to improve the properties of the MBE QD lasing
Colloidal synthesis:
Group II-VI semiconductor
Stability is good with core/shell structures
size dispersion is good, Shape is easy to be controlled
To fabricate electricallydriven device,
carriers’ injection and
transportion in colloidal
QDs should be improved
Colloidal CdSe quantum dots in our lab
Abs / PL Intensity (a.u.)
6.4 nm
5.6 nm
4.6 nm
3.9 nm
3.2 nm
2.9 nm
2.6 nm
350
400
450
500
550
600
650
700
Wavelength (nm)
UV-Vis absorption and photoluminescence (PL)
spectra of the as-prepared CdSe nanocrystals with
different sizes.
Digital picture of CdSe nanocrystal s in
toluene with different sizes under UV
illumination.
Colloidal Core/Shell quantum dots in our lab
Absorption (solid line) and PL spectra (dashed line) for bare-core CdSe NCs
and CdSe/CdS core/shell NCs with different shell thickness. Inset: PL QY
(circle) and PL FWHM (rectangle) of the CdSe/CdS core/shell NCs versus the
number of CdS ML.
Applications
Colloidal QDs have been synthesized successfully for about ten years,
but their optoelectronic application has not been commercially realized
yet. In the following, Quantum-confined Stark effect (QCSE), which
can be used in Optoelectronic modulators, is as an example.
Hez Hhz
E
Heh
Problem of QCSE in Colloidal QDs
phonon bottleneck effect
photoionization
random electric field
near the QDs
QCSE is an electric field effect
Science 278, 2114 (1997)
Clear ensemble QCSE shift has not been observed yet
We have observed a clear QCSE red-shift in
electroluminescent spectra
ITO/PVK:QDs/Al
Voltage-dependent EL
(Constant Temperature)
The EL peak exhibits a redshift when the
applied voltage is increased: Quantum-confined Stark effect
Strong ensemble QCSE absorption have been observed in
our lab
ITO/PVK:QDs/SiO2/ITO
polarizable character
The polarizability is 3.6×106 and 2.9×106 Å3 for the
first absorption peak and the emitting peak, respectively
Advantage:
broadening of the absorption peaks
weakening of the oscillator strength
tunneling of carriers out of confined zone
Due to 3D confinement, the QDs’ QCSE exbibits better Stark
behavior than QWs’ QCSE.
Nature 437, 1334 (2005)