Effect of ion damage on optical properties of ZnO films grown by plasma-assisted MBE

Abstract

The effect of plasma-induced ion damage on the optical prop erties of ZnO films grown by plasma-assisted molecularbeam epitaxy on a-sapphire substrates and GaN(0001)/ c-sapphire templates prepared has been studied using steady-stateand time-resolved photoluminescence. We observed that the deflecting the ions produced by the RF oxygen plasmaaway from substrate results in improved excitonic emission and modification of the defect-related PL spectrum. Theintensity of the near-band-edge lines in the photoluminescence spectra from the layers grown with the ion deflection was found to increase by factors 7 to 20 for the layers grown on GaN(0001)/ c-sapphire at a plasma power of 350 W and by 3 to 4 times for ZnO grown on a-sapphire substrates at a plasma power of265 W as compared to the controls grownwithout the ion deflection. The yellow-green spectral range was dominated by different defect bands in the films grownwith and without ion deflectio n. The effect of RF power on peak positions of the defect band was studied for the filmsgrown without ion deflection. For the ZnO films grown on a-plane sapphire substrates, time-resolved photoluminescenceshowed a significant increase in luminescence decay times both at RT and 89 K. However, for ZnO on GaN(0001)/c-sapphire substrates, virtually no improvement in decay time was found at 89 K with only a moderate increase in decayconstant at room temperature.Keywords: experiment, ZnO, molecular beam epitaxy, photoluminescence