Ultrafast electronic relaxation and charge-carrier localization in CdS/CdSe/CdS quantum-dot quantum-well heterostructures.
The relaxation and localization times of excited electrons in CdS/CdSe/CdS colloidal quantum wells were measured using subpicosecond spectroscopy. HRTEM analysis and steady-state PL demonstrate a narrow size distribution of 5-6 nm epitaxial crystallites. By monitoring the rise time of the stimulated emission as a function of pump intensity, the relaxation times of the electron from the CdS core into the CdSe well are determined and assigned. Two-component rise times in the stimulated emission are attributed to intraband relaxation of carriers generated directly within the CdSe well (fast component) and charge transfer of core-localized carriers across the CdS/CdSe interface (slow component). This is the first reported observation of simultaneous photon absorption in the core and well of a quantum-dot heterostructure. With increasing pump intensity, the charge-transfer channel between the CdS core CdSe well contributes less to the stimulated emission signal because of filling and saturation of the CdSe well state, making the interfacial charge-transfer component less efficient. The interfacial charge-transfer time of the excited electron was determined from the slow component of the stimulated emission build-up time and is found to have a value of 1.2 ps.
Schill
Alexander W
AW
Laser Dynamics Laboratory, Department of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, USA.
Gaddis
Christopher S
CS
Qian
Wei
W
El-Sayed
Mostafa A
MA
Cai
Ye
Y
Milam
Valeria T
VT
Sandhage
Kenneth
K
D019187:Cadmium Compounds / Q000737:chemistry*; D004579:Electron Transport; D036103:Nanotechnology / Q000295:instrumentation / Q000379:methods*; D045663:Quantum Dots; D018036:Selenium Compounds / Q000737:chemistry*; D012666:Semiconductors; D055672:Static Electricity; D013440:Sulfides / Q000737:chemistry*; D013997:Time Factors
D019187:Cadmium Compounds; D018036:Selenium Compounds; D013440:Sulfides; C034939:cadmium sulfide; C058667:cadmium selenide