Photoexcitation Carrier Kinetics in WSe2 Nanolayers in the Vicinity of the Band Edge

The photoexcitation and relaxation of carriers is studied in WSe2 nanolayers on Si/SiO2 substrate by optical pump-probe technique. The excitation wavelength falls in the vicinity of the band edge. The thickness variation of WSe2 layers acts as tuning of band gap of the layers. In this way, a band edge spectroscopy is carried out using the constant excitation wavelength. It is shown that the relaxation time constants increase with the thickness increase, while the amplitude of transient reflectivity changes nonmonotonically. A model is suggested describing the amplitude behavior.