Van der Waals-Zeeman Institute, University of Amsterdam, Science Park 904, NL-1098 XH Amsterdam, The Netherlands.
Nat Nanotechnol. 2011 Oct 9;6(11):710-3. doi: 10.1038/nnano.2011.167.
Carrier multiplication by generation of two or more electron-hole pairs following the absorption of a single photon may lead to improved photovoltaic efficiencies and has been observed in nanocrystals made from a variety of semiconductors, including silicon. However, with few exceptions, these reports have been based on indirect ultrafast techniques. Here, we present evidence of carrier multiplication in closely spaced silicon nanocrystals contained in a silicon dioxide matrix by measuring enhanced photoluminescence quantum yield. As the photon energy increases, the quantum yield is expected to remain constant, or to decrease as a result of new trapping and recombination channels being activated. Instead, we observe a step-like increase in quantum yield for larger photon energies that is characteristic of carrier multiplication. Modelling suggests that carrier multiplication is occurring with high efficiency and close to the energy conservation limit.
载流子倍增是指在吸收单个光子后产生两个或更多的电子-空穴对，这可能会提高光伏效率，并在包括硅在内的各种半导体制成的纳米晶体中得到了观察。然而，除了少数例外，这些报告都是基于间接的超快技术。在这里，我们通过测量增强的光致发光量子产率，提供了在二氧化硅基质中紧密间隔的硅纳米晶体中存在载流子倍增的证据。随着光子能量的增加，量子产率预计会保持不变，或者由于新的陷阱和复合通道被激活而减少。然而，我们观察到在较大的光子能量下，量子产率会出现阶跃式增加，这是载流子倍增的特征。模型表明，载流子倍增以高效率和接近能量守恒极限的方式发生。
