Ultrafast carrier dynamics, band-gap renormalization, and optical properties of ZnSe nanowires

In this paper, we present a comprehensive study of the carrier dynamics and optical properties of ZnSe nanowires (NWs). The transparency of the sample, obtained by the growth of the ZnSe NWs on glass, allowed us to perform transmittance, reflectance, photoluminescence (PL), time-resolved PL, and pump-probe transient absorption spectroscopy on as-grown samples. All measurements were performed at room temperature. Strong light trapping at the band-gap energy has been observed in reflectivity measurements. Fast transient absorption bleaching due to band filling and band-gap renormalization has been observed. The band-gap renormalization has a rise time constant of about 170 fs and a decay time of about 4 ps. Fast transient absorption bleaching is also observed at energies below the band gap, suggesting that intrinsic processes prevail over extrinsic photoinduced transitions in our high-quality NWs. The PL reveals the presence at room temperature of excitonic emission that shows a decay time of 0.5 ns. All of these features indicate that our ZnSe NWs have quality comparable to epitaxial films and can be used for optical devices and nonlinear optics.