Growth of low resistive Al-doped ZnCdO thin films with rocksalt structure for transparent conductive oxide thin films

Abstract

Recently, ZnCdO has received great attention in the TCO material for its high mobility. In this study, we have grown Al-doped Zn 1-x Cd x O (ZnCdO) thin films by molecular beam epitaxy on MgO (100) substrates. The wurtzite(WZ)-ZnCdO phase is observed on the composition $x=0.52$ whereas the rocksalt (RS)–ZnCdO phase is observed in for $\mathrm{x}\geq 0.70$ . Within the composition region of 0.55\leq x\leq 0.69$ , both the wurtzite and rocksalt phases co-exist. At the phase transition to RS at $x$ ∼ 0.70, the optical gap increases drastically to > 3.0 eV. The largest band gap energy is obtained as 3.23 eV in RS ( $\mathrm{x}=0.703$ ) phase. RS-ZnCdO thin films exhibit a low resistivity of $\sim 7\times 10^{-5} \Omega\text{cm}$ with a maximum mobility of ∼ 60 cm2/Vs and a high carrier concentration of $7\times 10^{20} \text{cm}^{-3}$ to $1\times 10^{21} \text{cm}^{-3}$ .