Changes of Carrier Density and Mobility in ALD-ZnO Thin Films after Nitrogen-ion Implantation

ZnO has attracted much attention due to its highly efficient UV emission resulting from its large band gap of 3.37 eV, large exciton binding energy of 60 meV, and low power threshold for optical pumping at room temperature. In this study, ZnO films were grown on glass substrates at a substrate temperature of 190 degrees C by using atomic layer deposition (ALD), and changes in the carrier density and mobility of the ZnO films after nitrogen-ion implantation were investigated. For ZnO film deposition, diethyl zinc was used as the metal-organic precursor, H2O as the oxidant, and Ar as the carrier and the purge gas. The film thickness after 1,800 cycles was measured to be approximately 450 nm, giving a growth rate of 0.25 nm/cycle. For nitrogen-ion implantation, the nitrogen-ion energy of 130 keV was determined by numerical simulation using the transport of ions in matter (TRIM) code, and the ZnO films were doped by using nitrogen-ion implantation at fluences of 1.0 x 10(15) ions/cm(2) similar to 1.0 x 10(17) ions/cm(2). The change in the carrier density of the ZnO film with increasing irradiation influence was found to be significant. At a fluence of 1.0 x 10(17) ions/cm(2), a drastic carrier density change of six orders of magnitude, from similar to 10(19) cm(-3) to similar to 10(13) cm(-3), was realized. The change in the magnitude of the mobility was found to be relatively small, and the magnitude was reduced by up to 80%.