Effect of lithium-ion implantation of varying fluence on the optical properties of ZnMgO

Abstract

The large bandgap (3.37 eV) and exciton binding energy (60 meV) makes ZnO most promising material in the area of optoelectronic devices. The efficiency of these devices can be enhanced by increasing the bandgap of those materials which is possible by band-gap engineering. It has been found that incorporation of Mg can increase the bandgap of the alloy up to 4 eV and even more. We investigated the optical properties of Zn_1-x Mg_xO film implanted by Li at low energy (40 KeV) with dosage of 5x10¹³ ions/cm² and 10¹⁴ ions/cm² respectively. Prior to implantation 150 nm Zn_1-xMg_xO (x=0.15) film was deposited on Si substrate followed by annealing at 650°C and 750°C. For dosage of 5x10¹³ ions/cm² and 10¹⁴ ions/cm²the low temperature (15K) and room temperature photoluminescence spectra is dominated by the emission of 3.66 eV which is the band gap energy of Zn_1-xMg_xO, shifts to 3.63 eV at higher dosage of ions. With increasing energy (50 KeV) this peak was revealed only at 5x10¹³ ions/cm^2.At 10¹⁴ ions/cm² no sign of this peak was visible. The splitting of conduction band and valence band into multiple sub-bands causes a transition between the subband of conduction band and sub-band of heavy-hole and an emission occurs at 3.58 eV referred as 11H. The existence of acceptor-bound exciton peak (A°X) around 3.33 eV and the presence of donor-to-acceptor-pair peak at 3.24 eV provide strong evidence of increased acceptor concentration.