Singh Vivek, Yu Yixuan, Sun Qi-C, Korgel Brian, Nagpal Prashant
Department of Chemical and Biological Engineering, University of Colorado Boulder, Boulder, Colorado 80303, USA.
Nanoscale. 2014 Dec 21;6(24):14643-7. doi: 10.1039/c4nr04688a. Epub 2014 Nov 4.
While silicon nanostructures are extensively used in electronics, the indirect bandgap of silicon poses challenges for optoelectronic applications like photovoltaics and light emitting diodes (LEDs). Here, we show that size-dependent pseudo-direct bandgap transitions in silicon nanocrystals dominate the interactions between (photoexcited) charge carriers and phonons, and hence the optoelectronic properties of silicon nanocrystals. Direct measurements of the electronic density of states (DOS) for different sized silicon nanocrystals reveal that these pseudo-direct transitions, likely arising from the nanocrystal surface, can couple with the quantum-confined silicon states. Moreover, we demonstrate that since these transitions determine the interactions of charge carriers with phonons, they change the light emission, absorption, charge carrier diffusion and phonon drag (Seebeck coefficient) in nanoscaled silicon semiconductors. Therefore, these results can have important implications for the design of optoelectronics and thermoelectric devices based on nanostructured silicon.
虽然硅纳米结构在电子学中被广泛使用，但硅的间接带隙给光伏和发光二极管（LED）等光电子应用带来了挑战。在此，我们表明硅纳米晶体中尺寸依赖的准直接带隙跃迁主导了（光激发）电荷载流子与声子之间的相互作用，进而主导了硅纳米晶体的光电子特性。对不同尺寸硅纳米晶体的电子态密度（DOS）进行直接测量表明，这些可能源自纳米晶体表面的准直接跃迁能够与量子限制的硅态耦合。此外，我们证明，由于这些跃迁决定了电荷载流子与声子的相互作用，它们改变了纳米级硅半导体中的光发射、吸收、电荷载流子扩散和声子拖曳（塞贝克系数）。因此，这些结果对于基于纳米结构硅的光电器件和热电器件的设计可能具有重要意义。
