胶体半导体量子点的光电性质研究 东南大学电子工程系 北京， 2009 年 5 月 张家雨，崔一平

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

MBE deposition group III-V, IV semiconductor Fabrication of Quantum Dots (QDs) 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 electrically- driven device, carriers’ injection and transportion in colloidal QDs should be improved

Colloidal CdSe quantum dots in our lab 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. Abs / PL Intensity (a.u.) Wavelength (nm) 2.6 nm 2.9 nm 3.2 nm 3.9 nm 4.6 nm 5.6 nm 6.4 nm

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. Colloidal Core/Shell quantum dots in our lab

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. E H ez H hz H eh

photoionization phonon bottleneck effect random electric field near the QDs Problem of QCSE in Colloidal QDs QCSE is an electric field effect Science 278, 2114 (1997) Clear ensemble QCSE shift has not been observed yet

The EL peak exhibits a redshift when the applied voltage is increased: Quantum-confined Stark effect Voltage-dependent EL (Constant Temperature) ITO/PVK:QDs/Al We have observed a clear QCSE red-shift in electroluminescent spectra

Strong ensemble QCSE absorption have been observed in our lab ITO/PVK:QDs/SiO 2 /ITO

polarizable character The polarizability is 3.6×10 6 and 2.9×10 6 Å 3 for the first absorption peak and the emitting peak, respectively

Advantage: tunneling of carriers out of confined zone broadening of the absorption peaks weakening of the oscillator strength Nature 437, 1334 (2005) Due to 3D confinement, the QDs’ QCSE exbibits better Stark behavior than QWs’ QCSE.