Structure and ultrafast carrier dynamics in n-type transparent Mo:ZnO nanocrystalline thin films

High quality ZnO and Mo-doped ZnO thin films were fabricated with a dc sputtering method, and XRD and Raman characterizations reveal that Mo atoms were successfully incorporated into ZnO lattice to form a n-type semiconductor. Two-color femtosecond pump and probe results indicate that charge carriers relaxation in pure ZnO film shows biexponential decay processes with an ultrafast component of about 1 ps and slow component of about 135 ps. For Mo-doped ZnO films, the charge carriers relaxation shows three exponential decay processes with an ultrafast part of 1 ps, fast part of about 10 ps and slow part of 135 ps. The 10 ps fast component relaxation process originates from the Mo-formation defects.