Photonics Research Group, INTEC Department, Ghent University-IMEC, Sint-Pietersnieuwstraat 41, 9000 Ghent, Belgium.
ACS Nano. 2012 Jul 24;6(7):6067-74. doi: 10.1021/nn301149x. Epub 2012 Jun 19.
Using femtosecond transient absorption spectroscopy, we demonstrate that lead chalcogenide nanocrystals show considerable photoinduced absorption (PA) in a broad wavelength range just below the band gap. The time-dependent decay of the PA signal correlates with the recovery of the band gap absorption, indicating that the same carriers are involved. On this basis, we assign this PA signal to intraband absorption, that is, the excitation of photogenerated carriers from the bottom of the conduction band or the top of the valence band to higher energy levels in the conduction and valence band continuum. We confirm our experiments with tight-binding calculations. This broadband response in the commercially interesting near- to mid-infrared range is very relevant for ultra-high-speed all-optical signal processing. We benchmark the performance with bulk Si and Si nanocrystals.
利用飞秒瞬态吸收光谱技术，我们证明了在略低于带隙的宽波长范围内，铅硫属纳米晶体表现出相当大的光致吸收（PA）。光致吸收信号的时间相关衰减与带隙吸收的恢复相关联，表明涉及相同的载流子。在此基础上，我们将此 PA 信号归因于内带吸收，即从导带底部或价带顶部激发光生载流子到导带和价带连续体中的更高能级。我们用紧束缚计算验证了我们的实验。在商业上有趣的近中红外范围内的这种宽带响应对于超高速度全光信号处理非常重要。我们用体硅和硅纳米晶体对其性能进行了基准测试。
