Spins Dynamics In Zinc-blende CdSe Quantum Dots

Semiconductor science and technology is one of the greatest scientific andtechnological achievements in the20th century, it also drives the innovation ofsemiconductor devices based on the electronic charge degrees of freedom. However,along with the ascension of circuit integration, thermal effect and quantum size effectwill be severely hampered the further development of the device. Spintronics arise atthis historic moment. The aim for a new generation of electronics with much higherstability, faster operation speed and lower power dissipation via exploiting the carrierspin degree of freedom motivates the studies in the field “semiconductor spintronics”.In quantum dots, the carriers are confined in all three dimensions, with the strongquantum confinement that the electrons exhibit a discrete energy spectrum rather thanquasi-continuous spectrum. According to the optical orientative transition rule，we caninject100%carrier spin polarization in theory. CdSe quantum dots is one of directband gap semiconductors, the energy structure is relatively simple, and its bad gap isassociated with visible wavelengths, which enable them to be an ideal material forbiological label and fluorescent display.Time resolved pump-probe measurement technology is used to study spindynamics in CdSe quantum dots. The main results of this article are concluded asfollowing:(1): X-Ray diffraction and TEM images revealed that our CdSe QDs havezinc-blend structure and narrow size distribution (less than5%). The size-dependenceof blue-shift in both absorption and emission spectra reveal that the confinementeffect plays dominant role in these CdSe QDs.(2): Longitudinal spin relaxation was studied in these CdSe quantum dots, itwas found that the hole spin relaxation time is about several picoseconds and isindependent to exciting energy fluence at room temperature.(3): Using time resolved Faraday ellipticity technology in the Voigt geometry westudied the coherent electron spin dynamics in colloidal CdSe QDs with zinc-blende structure at room temperature. Experimental results demonstrated that the electronspin coherence can persist up to several hundred ps at room temperature. Electronspin precession frequency almost showed no pump fluence and photo-excitationenergy dependence. The spin beat oscillation frequency increased linearly with themagnetic field and the slope of this dependence gave the value of the electron g-factor,and the magnitude of g-factor increased with decreasing dot size. The inhomogeneousspin dephasing time showed a nice1/B dependence for B>0.3T, which confirmed theinhomogeneous dephasing mechanism plays an important role in larger magneticfields.