Study A high mobility of p-AlN:ZnO thin films doped by RF sputtering

Abstract

Achieving high conductivity p-type zinc oxide (ZnO) thin films remains a great challenge, hence the need for co-doping with AlN via RF sputtering. RF sputtering was applied across a range of target power (150, 175, 200, 225 and 250 W) with Ar (20%) and N₂ (80%) at room temperature. ZnO (002) peak of wurzite structure showed in all the prepared films. Recombination of free excitons was identified using PL technique. The Raman peaks that denoted as ZnO:AlN and ZnO:N were shown at 578.58 cm^-1 and 276 cm^-1 respectively. AZO23 and AZO25 samples exhibited p-type conductivity behaviour with hole concentrations of 3.06 ×10^+ 16 cm^-3 and 1.83 ×10^+ 18 cm^-3 and matching mobilities of 117 cm² V^-1 s^-1and 19.1 cm² V^-1 s^-1, respectively. The p-type behavior of the ZnO sample doped at RF power of 175 W is due to the formation N-Al-N complex which serves as a shallow acceptor derived from the substitution of Zn^+ 2 ions with Al^+ 3 ions. On the other hand, the p-type behavior of the sample doped at RF power of 225 W can be due to the replacement of O^-2 ions site (radius of 0.140 nm) with the larger N^-3 ions (radius of 0.146 nm) and the formation (N)_O acceptors and (N₂)_O donors. Nonetheless, the effect of (N)_O acceptors is more significant than that of (N₂)_O donors, leading to the p-type conductivity observed in these samples. The higher mean free path/crystallite size (Ɩ/D) ratio recorded for the sample doped at 175 W accounts for its higher mobility (117 cm² V^-1 s^-1). Hence, RF power values of 175 and 225 W are effective for the successful doping of ZnO wuth AIN to obtain p-type ZnO.