胶体半导体量子点的光电性质研究
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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.

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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)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

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: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

Group II-VI semiconductor

Stability is good with core/shell structures

size dispersion is good, Shape is easy to be controlled

To fabricate electrically-driven device,

carriers’ injection and transportion in colloidal QDs should be improved


Colloidal 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CdSe quantum dots in our lab

6.4 nm

5.6 nm

4.6 nm

Abs / PL Intensity (a.u.)

3.9 nm

3.2 nm

Digital picture of CdSe nanocrystal s in toluene with different sizes under UV illumination.

2.9 nm

2.6 nm

Wavelength (nm)

UV-Vis absorption and photoluminescence (PL) spectra of the as-prepared CdSe nanocrystals with different sizes.


C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olloidal 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

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.

Hhz

Hez

E

Heh


Problem of QCSE in Colloidal QDs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

phonon bottleneck effect

photoionization

random electric field near the QDs

Science 278, 2114 (1997)

QCSE is an electric field effect

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 electroluminescent spectra in our lab

ITO/PVK:QDs/SiO2/ITO


polarizable character electroluminescent spectra

The polarizability is 3.6×106 and 2.9×106 Å3 for the first absorption peak and the emitting peak, respectively


broadening of the absorption peaks electroluminescent spectra

weakening of the oscillator strength

Advantage:

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)


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