Ultrafast time-resolved spectroscopy of ZnSe nanowires: Carrier dynamics of defect-related states

摘要

In recent years, ZnSe nanowires have been widely investigated for their potential applications in optoelectronics. A typical room temperature photoluminescence spectrum of ZnSe nanowires grown by vapor-liquid-solid growth under different growth conditions shows that the spectrum is dominated by two characteristic emission peaks. The first peak is attributed to the band edge emission peak at 2.68 eV whereas the second to the broad deep defect-related emission peak in the region of 1.8-2.4 eV. In this work, we present a study of ultrafast time-resolved spectroscopy of defect states of ZnSe nanowires grown under Se-rich growth conditions. We investigate in detail the carrier dynamics of these nanostructure materials using selective optical excitation femtosecond pulses from a wavelength tunable optical parametric amplifier system. The effects of intrinsic point defects inherent in the manufacturing of these materials and in particular the relaxations of the photogenerated carriers occupying these defect states are examined. Temporal dynamics on a few picoseconds time-scale provided information on effects such as state filling and secondary excitation and their contribution to the overall induced absorption. Long time-scale probing of induced absorption provided information on the defect states associated with the observed photoluminescence in this material.