Broadband and picosecond intraband absorption in lead-based colloidal quantum dots.
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.
Photonics Research Group, INTEC Department, Ghent University-IMEC, Sint-Pietersnieuwstraat 41, 9000 Ghent, Belgium.
Bram
B
De Geyter
Arjan J
AJ
Houtepen
Sergio
S
Carrillo
Pieter
P
Geiregat
Yunan
Y
Gao
Sybren
S
ten Cate
Juleon M
JM
Schins
Dries
D
Van Thourhout
Christophe
C
Delerue
Laurens D A
LD
Siebbeles
Zeger
Z
Hens