QUANTUM CONFINEMENT AND ULTRAFAST DEPHASING DYNAMICS IN INP NANOCRYSTALS

The electronic level structure and dephasing dynamics of InP nanocryst als in the strong quantum-confinement regime are studied by two comple mentary techniques: nanosecond hole burning and the femto-second three -pulse photon echo. Hole burning yields the homogeneous electronic lev el structure while the photon echo allows the extraction of the linewi dth of the band-gap transition. The congestion of electronic levels ob served close to the band-edge transition in the hole-burning experimen ts gives rise to a pulse-width-limited initial decay in the photon-ech o signal. The level structure is calculated and assigned using a model which includes valence band mixing. The homogeneous linewidth of the band-edge transition is approximately 5 meV at 20 K and is broadened c onsiderably at higher temperatures. The temperature dependence of the linewidth is consistent with an intrinsic dephasing mechanism of coupl ing to low-frequency acoustic modes mediated by the deformation potent ial. Quantum-confinement effects in III-V semiconductor InP are compar ed to those of the prototypical CdSe II-VI semiconductor nanocrystal s ystem.