PHYS 51 |
| In quantum dots, surfaces and the absence of linear momentum conservation, discrete electronic levels, and the stronger interaction between carriers modify the rates and mechanisms of electronic energy relaxation compared to bulk semiconductors. This talk discusses the energy relaxation of single and multiple excited carriers in quantum dot. With a single carrier, energy relaxation occurs by coupling to vibrations of the lattice and the surrounding surfactants or it may occur via intermediate defect states. Experimentally, the single electron limit is approached by charging the dots or by photoexcitation and subsequent hole extraction. The latter is performed with hole-surface traps and hole-extracting core/shell. Electron intraband relaxation slows from sub-ps to more than 30 ps but longer times should be achievable. Longer times will lead to efficient infrared emission. With multiple ambipolar carriers in a small dot, non-radiative recombination reduces fluorescence yields. For bulk semiconductors, textbooks assign this to an Auger process akin to atoms. I will describe experiments that test and contradict this underlying mechanism in quantum dots. This work requires core/shell synthesis which will be briefly discussed. |
|
Nanostructured Materials
1:20 PM-5:20 PM, Sunday, April 6, 2008 Morial Convention Center -- Rm. 338, Oral
Division of Physical Chemistry |